IB Biology SL Flashcards: Complete Course Review
Review the current IB Biology Standard Level course with 960 independently written active-recall cards covering all 34 SL topics across molecules, cells, organisms, genetics, evolution, and ecology.
Mayelana naleli qoqo
Study the current IB Biology SL course with 960 independently written English flashcards. The deck covers all 34 Standard Level topics through four broad groups: molecules and cells; metabolism and genetics; organisms and systems; and evolution and ecology.
Cards move from essential terms and structures to functions, mechanisms, comparisons, predictions, and compact interpretation prompts. Useful two-way term cards are separated by at least three unrelated cards, while explanatory answers are kept in the direction that supports meaningful recall. Every card carries the root tag ib-bio-sl and exactly one broad group tag.
The order introduces prerequisite ideas before dependent ones and progresses from simpler recall to more demanding reasoning within each topic. The deck is designed for ongoing spaced review. It does not replace data-heavy practice papers, extended-response practice, laboratory work, or the scientific investigation.
Reviewed in 2026 against the current Biology Standard Level course, first assessed in 2025.
Independent, unofficial study aid based on common biological knowledge. Not affiliated with or endorsed by the International Baccalaureate Organization. No copied IB examination questions, mark schemes, or curriculum text are included.
Check the official IB Biology course page for authoritative requirements.
Amakhadi akuleli qoqo
Ikhadi 1
Umbuzo
What is water polarity?
Impendulo
The unequal sharing of electrons in a water molecule, giving oxygen a partial negative charge and the hydrogens partial positive charges.
Ikhadi 2
Umbuzo
What is a hydrogen bond?
Impendulo
A weak attraction between a partially positive hydrogen atom and a partially negative atom in another molecule.
Ikhadi 3
Umbuzo
What is cohesion?
Impendulo
Attraction between molecules of the same substance.
Ikhadi 4
Umbuzo
What is adhesion?
Impendulo
Attraction between molecules of different substances.
Ikhadi 5
Umbuzo
Which term describes unequal charge distribution within a water molecule?
Impendulo
water polarity
Ikhadi 6
Umbuzo
Which term describes the intermolecular attraction that links neighboring water molecules?
Impendulo
a hydrogen bond
Ikhadi 7
Umbuzo
Which term describes attraction between molecules of the same substance?
Impendulo
cohesion
Ikhadi 8
Umbuzo
Which term describes attraction between water and a different material?
Impendulo
adhesion
Ikhadi 9
Umbuzo
What is a solvent?
Impendulo
A liquid that dissolves solutes to form a solution.
Ikhadi 10
Umbuzo
What is specific heat capacity?
Impendulo
The energy required to raise the temperature of a unit mass of a substance by one degree.
Ikhadi 11
Umbuzo
What is latent heat of vaporization?
Impendulo
The energy required to vaporize a specified amount of liquid without changing its temperature.
Ikhadi 12
Umbuzo
Why does ice float on liquid water?
Impendulo
Hydrogen bonds hold water molecules in an open lattice in ice, making ice less dense than liquid water.
Ikhadi 13
Umbuzo
Which term describes a liquid that dissolves solutes?
Impendulo
a solvent
Ikhadi 14
Umbuzo
Which term describes the energy needed to raise a unit mass by one degree?
Impendulo
specific heat capacity
Ikhadi 15
Umbuzo
Which term describes the energy needed to vaporize a liquid without a temperature change?
Impendulo
latent heat of vaporization
Ikhadi 16
Umbuzo
Which property of water makes sweating an effective cooling mechanism?
Impendulo
Water absorbs substantial energy as it evaporates; the highest-energy molecules leave, carrying heat away from the skin.
Ikhadi 17
Umbuzo
Why does water resist rapid temperature change?
Impendulo
Many hydrogen bonds must absorb energy before molecular motion increases substantially, giving water a high specific heat capacity.
Ikhadi 18
Umbuzo
How do cohesion and adhesion support water transport in narrow tubes?
Impendulo
Cohesion keeps water molecules connected, while adhesion helps the water column cling to the tube wall.
Ikhadi 19
Umbuzo
How does water participate differently in hydrolysis and condensation?
Impendulo
Hydrolysis consumes water to split a bond; condensation forms a bond and releases water.
Ikhadi 20
Umbuzo
How does floating ice protect aquatic life in winter?
Impendulo
Surface ice insulates the liquid water below, slowing further heat loss and preventing the whole body of water from freezing rapidly.
Ikhadi 21
Umbuzo
Why is water effective for transporting many biological solutes?
Impendulo
Its polarity allows ions and other polar molecules to become surrounded and dispersed in solution.
Ikhadi 22
Umbuzo
Why do nonpolar substances tend to cluster in water?
Impendulo
Clustering reduces the nonpolar surface exposed to water, allowing more water molecules to maintain hydrogen-bond interactions.
Ikhadi 23
Umbuzo
What is a nucleotide?
Impendulo
A nucleic-acid monomer made of a pentose sugar, a phosphate group, and a nitrogenous base.
Ikhadi 24
Umbuzo
What is a nucleoside?
Impendulo
A nitrogenous base joined to a pentose sugar, without a phosphate group.
Ikhadi 25
Umbuzo
What is a phosphodiester bond?
Impendulo
A covalent bond linking the phosphate of one nucleotide to the sugar of the next nucleotide.
Ikhadi 26
Umbuzo
What is DNA?
Impendulo
A usually double-stranded nucleic acid that stores hereditary information in its base sequence.
Ikhadi 27
Umbuzo
Which term describes a sugar-phosphate-base monomer?
Impendulo
a nucleotide
Ikhadi 28
Umbuzo
Which term describes a base joined to a sugar but no phosphate?
Impendulo
a nucleoside
Ikhadi 29
Umbuzo
Which term describes the covalent linkage in a nucleic-acid sugar-phosphate backbone?
Impendulo
a phosphodiester bond
Ikhadi 30
Umbuzo
Which term describes the nucleic acid that usually stores hereditary information?
Impendulo
DNA
Ikhadi 31
Umbuzo
What is RNA?
Impendulo
A usually single-stranded nucleic acid involved in expressing and regulating genetic information.
Ikhadi 32
Umbuzo
What are antiparallel DNA strands?
Impendulo
Two DNA strands that run in opposite 5′ to 3′ directions.
Ikhadi 33
Umbuzo
What is complementary base pairing?
Impendulo
Specific pairing in which adenine pairs with thymine in DNA, or uracil in RNA, and cytosine pairs with guanine.
Ikhadi 34
Umbuzo
What is a purine?
Impendulo
A nitrogenous base with two fused rings; adenine and guanine are purines.
Ikhadi 35
Umbuzo
Which term describes the usually single-stranded nucleic acid used in gene expression?
Impendulo
RNA
Ikhadi 36
Umbuzo
Which term describes DNA strands running in opposite directions?
Impendulo
antiparallel DNA strands
Ikhadi 37
Umbuzo
Which term describes specific A–T or A–U and C–G pairing?
Impendulo
complementary base pairing
Ikhadi 38
Umbuzo
Which term describes a two-ring nitrogenous base?
Impendulo
a purine
Ikhadi 39
Umbuzo
What is a pyrimidine?
Impendulo
A nitrogenous base with one ring; cytosine, thymine, and uracil are pyrimidines.
Ikhadi 40
Umbuzo
What is a genome?
Impendulo
The complete genetic material of an organism or cell.
Ikhadi 41
Umbuzo
What three structural features commonly distinguish RNA from DNA?
Impendulo
RNA usually contains ribose, uses uracil instead of thymine, and is single-stranded rather than double-stranded.
Ikhadi 42
Umbuzo
What determines the base sequence of the second DNA strand?
Impendulo
Complementary base-pairing rules determine it: A pairs with T, and C pairs with G.
Ikhadi 43
Umbuzo
Which term describes a one-ring nitrogenous base?
Impendulo
a pyrimidine
Ikhadi 44
Umbuzo
Which term describes the complete genetic material of an organism?
Impendulo
a genome
Ikhadi 45
Umbuzo
What do the 5′ and 3′ labels of a nucleic-acid strand refer to?
Impendulo
They refer to numbered carbon atoms in the pentose sugar and define the strand's chemical direction.
Ikhadi 46
Umbuzo
Where is genetic information encoded in DNA?
Impendulo
In the order of nitrogenous bases along the DNA strand.
Ikhadi 47
Umbuzo
Why is ATP classified as a nucleotide?
Impendulo
It contains adenine, ribose, and phosphate groups, the three component types of a nucleotide.
Ikhadi 48
Umbuzo
How do mRNA, tRNA, and rRNA contribute to protein synthesis?
Impendulo
mRNA carries the coding sequence, tRNA delivers amino acids, and rRNA forms the catalytic and structural core of ribosomes.
Ikhadi 49
Umbuzo
How are a gene and a chromosome related?
Impendulo
A gene is a DNA sequence with a biological function; a chromosome is one long DNA molecule containing many genes and other sequences.
Ikhadi 50
Umbuzo
What happens to double-stranded DNA when it is denatured by heat?
Impendulo
Hydrogen bonds between complementary bases break and the two strands separate; the covalent backbones usually remain intact.
Ikhadi 51
Umbuzo
Why can each DNA strand serve as a template during replication?
Impendulo
Its base sequence determines a complementary sequence through specific base pairing.
Ikhadi 52
Umbuzo
In which direction are new nucleic-acid strands synthesized?
Impendulo
Nucleotides are added to the 3′ end, so synthesis proceeds 5′ to 3′.
Ikhadi 53
Umbuzo
What is a monosaccharide?
Impendulo
A single sugar unit that can serve as a carbohydrate monomer.
Ikhadi 54
Umbuzo
What is a disaccharide?
Impendulo
A carbohydrate formed from two monosaccharides joined by a glycosidic bond.
Ikhadi 55
Umbuzo
What is a polysaccharide?
Impendulo
A polymer made from many monosaccharide units.
Ikhadi 56
Umbuzo
What is a glycosidic bond?
Impendulo
A covalent bond joining monosaccharides in a carbohydrate.
Ikhadi 57
Umbuzo
Which term describes a single sugar unit?
Impendulo
a monosaccharide
Ikhadi 58
Umbuzo
Which term describes two monosaccharides joined together?
Impendulo
a disaccharide
Ikhadi 59
Umbuzo
Which term describes a polymer of many sugar units?
Impendulo
a polysaccharide
Ikhadi 60
Umbuzo
Which term describes the covalent linkage between monosaccharides?
Impendulo
a glycosidic bond
Ikhadi 61
Umbuzo
What is a triglyceride?
Impendulo
A lipid formed from glycerol joined to three fatty acids.
Ikhadi 62
Umbuzo
What is a fatty acid?
Impendulo
A hydrocarbon chain with a carboxyl group that can form part of many lipids.
Ikhadi 63
Umbuzo
What is a saturated fatty acid?
Impendulo
A fatty acid with no carbon-carbon double bonds in its hydrocarbon chain.
Ikhadi 64
Umbuzo
What is a phospholipid?
Impendulo
An amphipathic lipid with a phosphate-containing hydrophilic head and hydrophobic fatty-acid tails.
Ikhadi 65
Umbuzo
Which term describes glycerol joined to three fatty acids?
Impendulo
a triglyceride
Ikhadi 66
Umbuzo
Which term describes a hydrocarbon chain ending in a carboxyl group?
Impendulo
a fatty acid
Ikhadi 67
Umbuzo
Which term describes a fatty acid without carbon-carbon double bonds?
Impendulo
a saturated fatty acid
Ikhadi 68
Umbuzo
Which term describes a lipid with a polar head and nonpolar tails?
Impendulo
a phospholipid
Ikhadi 69
Umbuzo
How is a glycosidic bond formed between two monosaccharides?
Impendulo
A condensation reaction joins them and releases a molecule of water.
Ikhadi 70
Umbuzo
How is a polysaccharide broken into smaller sugars?
Impendulo
Hydrolysis adds water across glycosidic bonds, splitting the polymer.
Ikhadi 71
Umbuzo
Which polysaccharides store glucose in plants and animals?
Impendulo
Starch stores glucose in plants; glycogen stores glucose in animals and fungi.
Ikhadi 72
Umbuzo
Why is cellulose suitable for plant cell walls?
Impendulo
Its straight β-glucose chains hydrogen-bond into strong microfibrils that resist stretching.
Ikhadi 73
Umbuzo
Why do lipids store more energy per gram than carbohydrates?
Impendulo
Lipids contain more energy-rich carbon-hydrogen bonds and are more reduced.
Ikhadi 74
Umbuzo
Why do phospholipids form bilayers in water?
Impendulo
Hydrophilic heads interact with water while hydrophobic tails cluster away from water.
Ikhadi 75
Umbuzo
Besides energy storage, what are three biological roles of lipids?
Impendulo
They form membranes, provide thermal insulation and cushioning, and can act as signaling molecules.
Ikhadi 76
Umbuzo
How do cis double bonds affect fatty-acid packing and melting point?
Impendulo
They introduce bends that reduce close packing, usually lowering the melting point.
Ikhadi 77
Umbuzo
What is an amino acid?
Impendulo
A protein monomer with an amino group, a carboxyl group, a hydrogen, and a variable R group attached to a central carbon.
Ikhadi 78
Umbuzo
What is a peptide bond?
Impendulo
The covalent bond formed between the amino group of one amino acid and the carboxyl group of another.
Ikhadi 79
Umbuzo
What is a polypeptide?
Impendulo
A chain of amino acids joined by peptide bonds.
Ikhadi 80
Umbuzo
What is protein primary structure?
Impendulo
The amino-acid sequence of a polypeptide.
Ikhadi 81
Umbuzo
Which term describes a protein monomer with amino, carboxyl, and variable R groups?
Impendulo
an amino acid
Ikhadi 82
Umbuzo
Which term describes the covalent linkage between amino acids?
Impendulo
a peptide bond
Ikhadi 83
Umbuzo
Which term describes a chain of peptide-linked amino acids?
Impendulo
a polypeptide
Ikhadi 84
Umbuzo
Which term describes a protein's amino-acid sequence?
Impendulo
protein primary structure
Ikhadi 85
Umbuzo
What is protein secondary structure?
Impendulo
Local folding such as α-helices and β-sheets stabilized mainly by backbone hydrogen bonds.
Ikhadi 86
Umbuzo
What is protein tertiary structure?
Impendulo
The overall three-dimensional shape of one polypeptide produced by interactions among R groups and the backbone.
Ikhadi 87
Umbuzo
What is protein quaternary structure?
Impendulo
The arrangement of multiple polypeptide subunits in one functional protein.
Ikhadi 88
Umbuzo
What is protein denaturation?
Impendulo
Loss of a protein's normal three-dimensional shape and therefore usually its function.
Ikhadi 89
Umbuzo
Which term describes local α-helix and β-sheet folding?
Impendulo
protein secondary structure
Ikhadi 90
Umbuzo
Which term describes the overall three-dimensional shape of one polypeptide?
Impendulo
protein tertiary structure
Ikhadi 91
Umbuzo
Which term describes the association of multiple polypeptide subunits?
Impendulo
protein quaternary structure
Ikhadi 92
Umbuzo
Which term describes loss of a protein's native shape?
Impendulo
protein denaturation
Ikhadi 93
Umbuzo
What mainly gives different amino acids their different chemical properties?
Impendulo
Their variable R groups.
Ikhadi 94
Umbuzo
What reaction forms a peptide bond?
Impendulo
A condensation reaction releases water as the amino and carboxyl groups join.
Ikhadi 95
Umbuzo
Why can high temperature denature a protein?
Impendulo
Increased molecular motion disrupts weak interactions that maintain the protein's shape.
Ikhadi 96
Umbuzo
Why can extreme pH denature a protein?
Impendulo
It changes the charges of R groups and disrupts ionic and hydrogen-bond interactions.
Ikhadi 97
Umbuzo
How do fibrous and globular proteins generally differ?
Impendulo
Fibrous proteins are elongated and mainly structural; globular proteins are compact and often perform dynamic functions.
Ikhadi 98
Umbuzo
Why is three-dimensional shape crucial to protein function?
Impendulo
It creates specific binding, catalytic, structural, or interaction surfaces.
Ikhadi 99
Umbuzo
Name four broad biological roles of proteins.
Impendulo
Catalysis, transport, signaling, defense, movement, and structural support are major roles; any four are sufficient.
Ikhadi 100
Umbuzo
How can changing one amino acid alter protein function?
Impendulo
The substitution can change R-group interactions, folding, stability, or an active or binding site.
Ikhadi 101
Umbuzo
What is cell theory?
Impendulo
The principles that living organisms are made of cells, cells are the basic units of life, and cells arise from pre-existing cells.
Ikhadi 102
Umbuzo
What is a prokaryotic cell?
Impendulo
A cell without a nucleus or other membrane-bound organelles.
Ikhadi 103
Umbuzo
What is a eukaryotic cell?
Impendulo
A cell with DNA enclosed in a nucleus and with membrane-bound organelles.
Ikhadi 104
Umbuzo
What is the nucleus?
Impendulo
The double-membrane organelle that contains most of a eukaryotic cell's DNA.
Ikhadi 105
Umbuzo
Which term describes the principles describing cells as life's basic units?
Impendulo
cell theory
Ikhadi 106
Umbuzo
Which term describes a cell lacking a nucleus and membrane-bound organelles?
Impendulo
a prokaryotic cell
Ikhadi 107
Umbuzo
Which term describes a cell with a nucleus and membrane-bound organelles?
Impendulo
a eukaryotic cell
Ikhadi 108
Umbuzo
Which term describes the organelle containing most eukaryotic DNA?
Impendulo
the nucleus
Ikhadi 109
Umbuzo
What is a ribosome?
Impendulo
A molecular complex of rRNA and proteins that synthesizes polypeptides.
Ikhadi 110
Umbuzo
What is the cytoplasm?
Impendulo
The material inside the plasma membrane but outside the nucleus, including cytosol and organelles.
Ikhadi 111
Umbuzo
What is the plasma membrane?
Impendulo
The selectively permeable boundary separating a cell from its environment.
Ikhadi 112
Umbuzo
What is a cell wall?
Impendulo
A rigid extracellular layer that supports and protects cells in plants, fungi, and most prokaryotes.
Ikhadi 113
Umbuzo
Which term describes the complex that synthesizes polypeptides?
Impendulo
a ribosome
Ikhadi 114
Umbuzo
Which term describes cell contents inside the plasma membrane but outside the nucleus?
Impendulo
the cytoplasm
Ikhadi 115
Umbuzo
Which term describes the selectively permeable cell boundary?
Impendulo
the plasma membrane
Ikhadi 116
Umbuzo
Which term describes a rigid extracellular support layer?
Impendulo
a cell wall
Ikhadi 117
Umbuzo
What is the nucleoid?
Impendulo
The non-membrane-bound region containing the main chromosome of a prokaryotic cell.
Ikhadi 118
Umbuzo
What is the cytoskeleton?
Impendulo
A dynamic network of protein filaments involved in cell shape, transport, division, and movement.
Ikhadi 119
Umbuzo
What structures are shared by all cells?
Impendulo
A plasma membrane, cytoplasm, genetic material, and ribosomes.
Ikhadi 120
Umbuzo
Which structures distinguish a typical plant cell from a typical animal cell?
Impendulo
A plant cell has a cellulose wall, chloroplasts in photosynthetic tissues, and a large central vacuole; an animal cell lacks these.
Ikhadi 121
Umbuzo
Which term describes the prokaryotic chromosome-containing region?
Impendulo
the nucleoid
Ikhadi 122
Umbuzo
Which term describes the internal network of protein filaments?
Impendulo
the cytoskeleton
Ikhadi 123
Umbuzo
How is genetic material commonly organized in a prokaryotic cell?
Impendulo
The main DNA is usually one circular chromosome in the nucleoid, often accompanied by smaller plasmids.
Ikhadi 124
Umbuzo
How is microscope magnification calculated?
Impendulo
Magnification = image size ÷ actual size, using the same units.
Ikhadi 125
Umbuzo
What does microscope resolution describe?
Impendulo
The ability to distinguish two close points as separate.
Ikhadi 126
Umbuzo
Arrange these from smallest to largest: ribosome, bacterium, animal cell.
Impendulo
Ribosome, bacterium, animal cell.
Ikhadi 127
Umbuzo
How does the cytoskeleton support intracellular transport?
Impendulo
Motor proteins move vesicles and other cargo along cytoskeletal filaments.
Ikhadi 128
Umbuzo
Why does a small cell usually exchange materials more efficiently than a geometrically similar large cell?
Impendulo
It has a larger surface-area-to-volume ratio, providing more exchange surface per unit of cell contents.
Ikhadi 129
Umbuzo
Why is a cell more than a collection of isolated molecules?
Impendulo
Organized interactions among components produce emergent functions such as metabolism, regulation, and reproduction.
Ikhadi 130
Umbuzo
What major advantage do membrane-bound organelles give eukaryotic cells?
Impendulo
They separate incompatible reactions and create specialized local conditions.
Ikhadi 131
Umbuzo
What is a phospholipid bilayer?
Impendulo
A double layer of phospholipids with hydrophilic heads facing water and hydrophobic tails facing inward.
Ikhadi 132
Umbuzo
What is the fluid mosaic model?
Impendulo
A model describing membranes as mobile phospholipids containing a changing mosaic of proteins and other components.
Ikhadi 133
Umbuzo
What is an integral membrane protein?
Impendulo
A protein embedded in the bilayer, often spanning it.
Ikhadi 134
Umbuzo
What is a peripheral membrane protein?
Impendulo
A protein attached to a membrane surface rather than embedded in the bilayer.
Ikhadi 135
Umbuzo
Which term describes a double phospholipid layer with inward-facing tails?
Impendulo
a phospholipid bilayer
Ikhadi 136
Umbuzo
Which term describes the model of a mobile lipid layer containing varied proteins?
Impendulo
the fluid mosaic model
Ikhadi 137
Umbuzo
Which term describes a protein embedded within the lipid bilayer?
Impendulo
an integral membrane protein
Ikhadi 138
Umbuzo
Which term describes a protein attached to a membrane surface?
Impendulo
a peripheral membrane protein
Ikhadi 139
Umbuzo
What is membrane cholesterol?
Impendulo
An amphipathic lipid that buffers membrane fluidity and reduces permeability in animal cells.
Ikhadi 140
Umbuzo
What is a glycoprotein?
Impendulo
A protein with an attached carbohydrate chain, often used in recognition, adhesion, or signaling.
Ikhadi 141
Umbuzo
What is diffusion?
Impendulo
Net movement of particles from a region of higher concentration to lower concentration due to random motion.
Ikhadi 142
Umbuzo
What is osmosis?
Impendulo
Net movement of water across a selectively permeable membrane from higher water potential to lower water potential.
Ikhadi 143
Umbuzo
Which term describes the animal-membrane lipid that buffers fluidity?
Impendulo
membrane cholesterol
Ikhadi 144
Umbuzo
Which term describes a carbohydrate-bearing protein?
Impendulo
a glycoprotein
Ikhadi 145
Umbuzo
Which term describes net movement down a concentration gradient?
Impendulo
diffusion
Ikhadi 146
Umbuzo
Which term describes net water movement across a selectively permeable membrane?
Impendulo
osmosis
Ikhadi 147
Umbuzo
What is facilitated diffusion?
Impendulo
Passive movement down a gradient through a membrane channel or carrier protein.
Ikhadi 148
Umbuzo
What is active transport?
Impendulo
Energy-requiring movement of a substance against its concentration or electrochemical gradient.
Ikhadi 149
Umbuzo
Why is the phospholipid bilayer selectively permeable?
Impendulo
Its hydrophobic interior allows small nonpolar molecules through more readily than ions and most large or polar molecules.
Ikhadi 150
Umbuzo
How do simple diffusion and facilitated diffusion differ?
Impendulo
Both are passive, but facilitated diffusion uses specific membrane proteins while simple diffusion passes through the bilayer.
Ikhadi 151
Umbuzo
Which term describes passive transport through a channel or carrier?
Impendulo
facilitated diffusion
Ikhadi 152
Umbuzo
Which term describes energy-dependent transport against a gradient?
Impendulo
active transport
Ikhadi 153
Umbuzo
How do channel and carrier proteins differ?
Impendulo
Channels provide hydrophilic pores; carriers bind solutes and change shape to move them.
Ikhadi 154
Umbuzo
How can an ATP-driven pump maintain an ion gradient?
Impendulo
It couples ATP hydrolysis to a conformational change that moves ions against their electrochemical gradient.
Ikhadi 155
Umbuzo
How does endocytosis move material into a cell?
Impendulo
The plasma membrane folds inward and pinches off a vesicle containing the material.
Ikhadi 156
Umbuzo
How does exocytosis move material out of a cell?
Impendulo
An intracellular vesicle fuses with the plasma membrane and releases its contents outside.
Ikhadi 157
Umbuzo
What happens to an animal cell in a strongly hypotonic solution?
Impendulo
Water enters by osmosis; without a cell wall, the cell may swell and lyse.
Ikhadi 158
Umbuzo
Does molecular movement stop when diffusion reaches equilibrium?
Impendulo
No. Molecules continue moving randomly, but there is no net movement between regions.
Ikhadi 159
Umbuzo
How does decreasing temperature generally affect membrane fluidity?
Impendulo
It reduces phospholipid movement and makes the membrane less fluid.
Ikhadi 160
Umbuzo
Why do unsaturated fatty-acid tails increase membrane fluidity?
Impendulo
Their cis double-bond bends prevent phospholipids from packing tightly.
Ikhadi 161
Umbuzo
What changes increase the rate of simple diffusion across a membrane?
Impendulo
A steeper gradient, larger surface area, higher temperature, shorter distance, and greater membrane permeability increase the rate.
Ikhadi 162
Umbuzo
What is a mitochondrion?
Impendulo
A double-membrane organelle where most aerobic ATP production occurs.
Ikhadi 163
Umbuzo
What is a chloroplast?
Impendulo
A double-membrane organelle where photosynthesis occurs in plants and algae.
Ikhadi 164
Umbuzo
What is rough endoplasmic reticulum?
Impendulo
A membrane network bearing ribosomes that synthesizes and begins processing many secreted and membrane proteins.
Ikhadi 165
Umbuzo
What is smooth endoplasmic reticulum?
Impendulo
A membrane network involved in lipid synthesis, detoxification, and calcium storage.
Ikhadi 166
Umbuzo
Which term describes the main organelle of aerobic ATP production?
Impendulo
a mitochondrion
Ikhadi 167
Umbuzo
Which term describes the photosynthetic organelle of plants and algae?
Impendulo
a chloroplast
Ikhadi 168
Umbuzo
Which term describes the ribosome-studded membrane network?
Impendulo
rough endoplasmic reticulum
Ikhadi 169
Umbuzo
Which term describes the membrane network that lacks ribosomes and synthesizes lipids?
Impendulo
smooth endoplasmic reticulum
Ikhadi 170
Umbuzo
What is the Golgi apparatus?
Impendulo
Stacked membranes that modify, sort, and package proteins and lipids into vesicles.
Ikhadi 171
Umbuzo
What is a lysosome?
Impendulo
An acidic enzyme-containing organelle that digests macromolecules and worn cellular components.
Ikhadi 172
Umbuzo
What is a vesicle?
Impendulo
A small membrane-bound compartment used for transport, storage, or chemical reactions.
Ikhadi 173
Umbuzo
What is the central vacuole?
Impendulo
A large plant-cell compartment that stores solutes and helps maintain turgor pressure.
Ikhadi 174
Umbuzo
Which term describes the organelle that modifies and sorts cellular cargo?
Impendulo
the Golgi apparatus
Ikhadi 175
Umbuzo
Which term describes the acidic digestive organelle?
Impendulo
a lysosome
Ikhadi 176
Umbuzo
Which term describes a small membrane-bound transport compartment?
Impendulo
a vesicle
Ikhadi 177
Umbuzo
Which term describes the large plant compartment that supports turgor?
Impendulo
the central vacuole
Ikhadi 178
Umbuzo
Why can compartmentalization increase metabolic efficiency?
Impendulo
It concentrates enzymes and substrates, maintains suitable local conditions, and separates incompatible reactions.
Ikhadi 179
Umbuzo
How do mitochondrial cristae support ATP production?
Impendulo
They increase inner-membrane area for electron transport chains and ATP synthase.
Ikhadi 180
Umbuzo
Why are chloroplast thylakoids arranged as extensive membranes?
Impendulo
They provide a large surface for light-absorbing complexes, electron transport chains, and ATP synthase.
Ikhadi 181
Umbuzo
What is the main function of the nucleolus?
Impendulo
It produces rRNA and assembles ribosomal subunits.
Ikhadi 182
Umbuzo
Trace a secreted protein from synthesis to release.
Impendulo
Ribosome on rough ER → ER lumen → transport vesicle → Golgi apparatus → secretory vesicle → plasma membrane → exocytosis.
Ikhadi 183
Umbuzo
Why does a lysosome maintain an acidic interior?
Impendulo
Its hydrolytic enzymes work best at low pH, and acidity helps confine their activity from the cytosol.
Ikhadi 184
Umbuzo
How do the nucleus, ribosomes, ER, and Golgi cooperate in protein production?
Impendulo
DNA instructions are transcribed in the nucleus; ribosomes translate them; ER folds or modifies many products; Golgi further modifies and sorts them.
Ikhadi 185
Umbuzo
How are transport vesicles directed to the correct target membrane?
Impendulo
Specific recognition proteins on vesicles and target membranes interact, allowing selective docking and fusion.
Ikhadi 186
Umbuzo
What is cell differentiation?
Impendulo
The process by which a cell develops specialized structure and function.
Ikhadi 187
Umbuzo
What is a stem cell?
Impendulo
An unspecialized cell able to self-renew and produce differentiated cells.
Ikhadi 188
Umbuzo
What is gene expression?
Impendulo
Use of genetic information to produce a functional RNA or protein product.
Ikhadi 189
Umbuzo
What is a tissue?
Impendulo
A coordinated group of similar or related cells performing a shared function.
Ikhadi 190
Umbuzo
Which term describes development of specialized cell structure and function?
Impendulo
cell differentiation
Ikhadi 191
Umbuzo
Which term describes an unspecialized self-renewing cell?
Impendulo
a stem cell
Ikhadi 192
Umbuzo
Which term describes production of a functional product from genetic information?
Impendulo
gene expression
Ikhadi 193
Umbuzo
Which term describes a group of coordinated cells with a shared function?
Impendulo
a tissue
Ikhadi 194
Umbuzo
What is an organ?
Impendulo
A structure made of multiple tissues working together for particular functions.
Ikhadi 195
Umbuzo
What is the organ-system level of biological organization?
Impendulo
A group of organs that coordinate to perform major functions for an organism.
Ikhadi 196
Umbuzo
What is surface-area-to-volume ratio?
Impendulo
The amount of surface area available relative to the volume it must serve.
Ikhadi 197
Umbuzo
How can two specialized cells have the same genome but different structures?
Impendulo
They express different sets and amounts of genes, producing different proteins and cellular features.
Ikhadi 198
Umbuzo
Which term describes a structure composed of multiple tissue types?
Impendulo
an organ
Ikhadi 199
Umbuzo
Which term describes the level of biological organization formed by coordinated organs?
Impendulo
an organ system
Ikhadi 200
Umbuzo
Which term describes surface area available per unit volume?
Impendulo
surface-area-to-volume ratio
Ikhadi 201
Umbuzo
How is a mammalian red blood cell specialized for oxygen transport?
Impendulo
Its biconcave shape increases exchange area, it is flexible, and loss of its nucleus leaves more space for hemoglobin.
Ikhadi 202
Umbuzo
How is a sperm cell specialized for fertilization?
Impendulo
It has a flagellum for movement, many mitochondria for ATP, a haploid nucleus, and an acrosome containing enzymes.
Ikhadi 203
Umbuzo
How is a neuron specialized for rapid communication?
Impendulo
Long processes carry signals over distance, branching dendrites receive inputs, and synaptic terminals transmit signals to other cells.
Ikhadi 204
Umbuzo
How is a root hair cell specialized for mineral and water uptake?
Impendulo
Its long projection increases surface area, its thin wall shortens the pathway, and membrane transport proteins take up ions.
Ikhadi 205
Umbuzo
How is a palisade mesophyll cell specialized for photosynthesis?
Impendulo
It contains many chloroplasts and is positioned near the upper leaf surface where light is strongest.
Ikhadi 206
Umbuzo
How do ciliated epithelial cells help protect airways?
Impendulo
Their cilia move mucus containing trapped particles and microbes toward the throat.
Ikhadi 207
Umbuzo
Why can extreme specialization reduce a cell's independence?
Impendulo
Resources and structures are committed to a narrow role, so the cell depends on other cells for functions it no longer performs well.
Ikhadi 208
Umbuzo
What is water potential?
Impendulo
The potential energy of water per unit volume relative to pure water, used to predict the direction of water movement.
Ikhadi 209
Umbuzo
What is solute potential?
Impendulo
The negative contribution of dissolved solutes to water potential.
Ikhadi 210
Umbuzo
What is pressure potential?
Impendulo
The contribution of physical pressure to water potential.
Ikhadi 211
Umbuzo
What is turgor pressure?
Impendulo
Outward pressure of a plant-cell interior against its cell wall after water uptake.
Ikhadi 212
Umbuzo
Which term describes the tendency of water to move relative to pure water?
Impendulo
water potential
Ikhadi 213
Umbuzo
Which term describes the water-potential component lowered by dissolved solutes?
Impendulo
solute potential
Ikhadi 214
Umbuzo
Which term describes the water-potential component caused by physical pressure?
Impendulo
pressure potential
Ikhadi 215
Umbuzo
Which term describes pressure of plant-cell contents against the wall?
Impendulo
turgor pressure
Ikhadi 216
Umbuzo
What is plasmolysis?
Impendulo
Separation of the plasma membrane from the cell wall after a plant cell loses water.
Ikhadi 217
Umbuzo
What is a flaccid plant cell?
Impendulo
A plant cell with insufficient turgor pressure to be firm.
Ikhadi 218
Umbuzo
What is an isotonic condition?
Impendulo
A condition in which two solutions have equal effective water potential and no net water movement occurs.
Ikhadi 219
Umbuzo
In which direction does water move across a permeable membrane?
Impendulo
From higher water potential to lower water potential.
Ikhadi 220
Umbuzo
Which term describes membrane separation from the plant cell wall after water loss?
Impendulo
plasmolysis
Ikhadi 221
Umbuzo
Which term describes a plant cell lacking firm turgor?
Impendulo
a flaccid plant cell
Ikhadi 222
Umbuzo
Which term describes equal effective water potential across a membrane?
Impendulo
an isotonic condition
Ikhadi 223
Umbuzo
What is the water potential of pure water at standard pressure?
Impendulo
Zero; adding solute makes water potential more negative.
Ikhadi 224
Umbuzo
How are water potential, solute potential, and pressure potential related?
Impendulo
Water potential equals solute potential plus pressure potential: Ψ = Ψs + Ψp.
Ikhadi 225
Umbuzo
Why does a plant cell usually become turgid rather than burst in a hypotonic solution?
Impendulo
Water entry raises pressure potential, while the rigid cell wall resists further expansion.
Ikhadi 226
Umbuzo
What happens to a plant cell placed in a solution with much lower water potential?
Impendulo
Water leaves the cell, turgor falls, and severe loss can cause plasmolysis.
Ikhadi 227
Umbuzo
Can two solutions have different solute concentrations but equal water potential?
Impendulo
Yes. A difference in pressure potential can offset a difference in solute potential.
Ikhadi 228
Umbuzo
What is an enzyme?
Impendulo
A biological catalyst that increases reaction rate without being consumed.
Ikhadi 229
Umbuzo
What is an active site?
Impendulo
The region of an enzyme where substrate binds and catalysis occurs.
Ikhadi 230
Umbuzo
What is a substrate?
Impendulo
A reactant molecule on which an enzyme acts.
Ikhadi 231
Umbuzo
What is activation energy?
Impendulo
The minimum energy input needed for a reaction to begin.
Ikhadi 232
Umbuzo
Which term describes a biological catalyst?
Impendulo
an enzyme
Ikhadi 233
Umbuzo
Which term describes the substrate-binding catalytic region of an enzyme?
Impendulo
an active site
Ikhadi 234
Umbuzo
Which term describes a reactant bound and changed by an enzyme?
Impendulo
a substrate
Ikhadi 235
Umbuzo
Which term describes the energy barrier that must be overcome for a reaction?
Impendulo
activation energy
Ikhadi 236
Umbuzo
What is the induced-fit model?
Impendulo
The model in which substrate binding changes active-site shape to improve catalytic interactions.
Ikhadi 237
Umbuzo
What is enzyme denaturation?
Impendulo
Loss of the active three-dimensional shape of an enzyme, usually causing loss of activity.
Ikhadi 238
Umbuzo
What is competitive inhibition?
Impendulo
Inhibition caused by a molecule competing with substrate for the active site.
Ikhadi 239
Umbuzo
What is noncompetitive inhibition?
Impendulo
Inhibition caused by binding away from the active site and reducing catalytic function.
Ikhadi 240
Umbuzo
Which term describes the model where substrate binding reshapes the active site?
Impendulo
the induced-fit model
Ikhadi 241
Umbuzo
Which term describes loss of an enzyme's functional shape?
Impendulo
enzyme denaturation
Ikhadi 242
Umbuzo
Which term describes inhibition by active-site competition?
Impendulo
competitive inhibition
Ikhadi 243
Umbuzo
Which term describes inhibition by binding outside the active site?
Impendulo
noncompetitive inhibition
Ikhadi 244
Umbuzo
What is an enzyme optimum?
Impendulo
The condition, such as temperature or pH, at which an enzyme's activity is highest.
Ikhadi 245
Umbuzo
What is feedback inhibition?
Impendulo
Control in which a pathway product inhibits an enzyme acting earlier in the pathway.
Ikhadi 246
Umbuzo
How does an enzyme increase reaction rate?
Impendulo
It stabilizes the transition state and provides a pathway with lower activation energy.
Ikhadi 247
Umbuzo
Why does enzyme activity often rise and then fall as temperature increases?
Impendulo
Molecular collisions initially increase, but excessive heat disrupts enzyme shape and denatures the active site.
Ikhadi 248
Umbuzo
Which term describes the condition producing maximum enzyme activity?
Impendulo
an enzyme optimum
Ikhadi 249
Umbuzo
Which term describes pathway control by inhibition from an end product?
Impendulo
feedback inhibition
Ikhadi 250
Umbuzo
Why does each enzyme have a characteristic pH range?
Impendulo
pH changes the ionization of amino-acid side chains, affecting active-site shape and chemical interactions.
Ikhadi 251
Umbuzo
Why does increasing substrate concentration eventually stop increasing enzyme rate?
Impendulo
At saturation, nearly all active sites are occupied and enzyme concentration limits the maximum rate.
Ikhadi 252
Umbuzo
How does increasing enzyme concentration affect rate when substrate is abundant?
Impendulo
More active sites are available, so the initial rate increases roughly in proportion to enzyme concentration.
Ikhadi 253
Umbuzo
What gives an enzyme substrate specificity?
Impendulo
The active site's shape, charge, polarity, and chemical groups complement particular substrates and transition states.
Ikhadi 254
Umbuzo
What is one practical advantage of immobilizing an enzyme?
Impendulo
The enzyme can be separated from products and reused while conditions around it are controlled.
Ikhadi 255
Umbuzo
Does an enzyme change a reaction's equilibrium position?
Impendulo
No. It speeds forward and reverse reactions but does not change the equilibrium constant or final equilibrium position.
Ikhadi 256
Umbuzo
How can high substrate concentration reduce competitive inhibition?
Impendulo
More substrate molecules increase the chance that substrate rather than inhibitor occupies the active site.
Ikhadi 257
Umbuzo
Why are metabolic reactions commonly organized into pathways?
Impendulo
A sequence of enzyme-controlled steps allows energy changes and intermediates to be controlled and coupled.
Ikhadi 258
Umbuzo
What is ATP?
Impendulo
A nucleotide that transfers usable energy through coupling of its hydrolysis to cellular processes.
Ikhadi 259
Umbuzo
What is cellular respiration?
Impendulo
Controlled release of energy from organic molecules to produce ATP.
Ikhadi 260
Umbuzo
What is glycolysis?
Impendulo
A cytosolic pathway that splits glucose into two pyruvate molecules and yields a small amount of ATP and reduced electron carriers.
Ikhadi 261
Umbuzo
What is pyruvate?
Impendulo
The three-carbon product of glycolysis that can enter aerobic or anaerobic pathways.
Ikhadi 262
Umbuzo
Which term describes the cell's immediate phosphoryl-group energy carrier?
Impendulo
ATP
Ikhadi 263
Umbuzo
Which term describes controlled ATP-producing breakdown of organic molecules?
Impendulo
cellular respiration
Ikhadi 264
Umbuzo
Which term describes the cytosolic splitting of glucose into pyruvate?
Impendulo
glycolysis
Ikhadi 265
Umbuzo
Which term describes the three-carbon product of glycolysis?
Impendulo
pyruvate
Ikhadi 266
Umbuzo
What is aerobic respiration?
Impendulo
Respiration that uses oxygen as the final electron acceptor and produces much more ATP than fermentation.
Ikhadi 267
Umbuzo
What is anaerobic metabolism?
Impendulo
ATP-producing metabolism that proceeds without oxygen.
Ikhadi 268
Umbuzo
What is fermentation?
Impendulo
An anaerobic pathway that regenerates oxidized electron carriers so glycolysis can continue.
Ikhadi 269
Umbuzo
What is oxidation?
Impendulo
Loss of electrons, often accompanied in biology by loss of hydrogen or gain of oxygen.
Ikhadi 270
Umbuzo
Which term describes respiration using oxygen as final electron acceptor?
Impendulo
aerobic respiration
Ikhadi 271
Umbuzo
Which term describes ATP-producing metabolism without oxygen?
Impendulo
anaerobic metabolism
Ikhadi 272
Umbuzo
Which term describes anaerobic regeneration of electron carriers after glycolysis?
Impendulo
fermentation
Ikhadi 273
Umbuzo
Which term describes loss of electrons?
Impendulo
oxidation
Ikhadi 274
Umbuzo
What is reduction?
Impendulo
Gain of electrons, often accompanied in biology by gain of hydrogen or loss of oxygen.
Ikhadi 275
Umbuzo
What is a reduced electron carrier?
Impendulo
A molecule such as NADH that carries high-energy electrons and hydrogen from one reaction to another.
Ikhadi 276
Umbuzo
What is chemiosmosis?
Impendulo
ATP production driven by ions moving down an electrochemical gradient through ATP synthase.
Ikhadi 277
Umbuzo
What is the overall word equation for aerobic respiration of glucose?
Impendulo
Glucose + oxygen → carbon dioxide + water + energy transferred to ATP and heat.
Ikhadi 278
Umbuzo
Which term describes gain of electrons?
Impendulo
reduction
Ikhadi 279
Umbuzo
Which term describes a molecule carrying high-energy electrons between reactions?
Impendulo
a reduced electron carrier
Ikhadi 280
Umbuzo
Which term describes ATP production powered by an ion gradient?
Impendulo
chemiosmosis
Ikhadi 281
Umbuzo
Where does glycolysis occur?
Impendulo
In the cytosol.
Ikhadi 282
Umbuzo
What major stages of aerobic respiration occur in mitochondria?
Impendulo
Pyruvate oxidation and the citric acid cycle occur in the matrix; electron transport and chemiosmosis occur at the inner membrane.
Ikhadi 283
Umbuzo
What is oxygen's direct role in aerobic respiration?
Impendulo
It accepts electrons and hydrogen ions at the end of the electron transport chain, forming water.
Ikhadi 284
Umbuzo
Why does aerobic respiration yield much more ATP per glucose than fermentation?
Impendulo
It transfers electrons through an electron transport chain and uses oxidative phosphorylation, extracting far more of glucose's energy.
Ikhadi 285
Umbuzo
What is the purpose of lactate formation in oxygen-limited animal cells?
Impendulo
It regenerates NAD⁺ so glycolysis can continue producing a small amount of ATP.
Ikhadi 286
Umbuzo
What products are formed during alcoholic fermentation in yeast?
Impendulo
Ethanol and carbon dioxide, while NAD⁺ is regenerated.
Ikhadi 287
Umbuzo
Why is some energy released by respiration transferred as heat rather than captured in ATP?
Impendulo
Energy conversions are not fully efficient, so part of the chemical energy becomes disordered molecular motion.
Ikhadi 288
Umbuzo
What is substrate-level phosphorylation?
Impendulo
Direct transfer of a phosphate group from a metabolic intermediate to ADP to form ATP.
Ikhadi 289
Umbuzo
How does electron transport lead to ATP synthesis in mitochondria?
Impendulo
Electron energy pumps protons across the inner membrane; proton flow back through ATP synthase drives ATP formation.
Ikhadi 290
Umbuzo
Why can intense exercise increase lactate production?
Impendulo
ATP demand can exceed oxygen delivery and aerobic capacity, so cells regenerate NAD⁺ through lactate formation to sustain glycolysis.
Ikhadi 291
Umbuzo
What is photosynthesis?
Impendulo
Conversion of light energy into chemical energy used to synthesize organic molecules from carbon dioxide.
Ikhadi 292
Umbuzo
What is chlorophyll?
Impendulo
A green pigment that absorbs light energy for photosynthesis.
Ikhadi 293
Umbuzo
What is an absorption spectrum?
Impendulo
A graph showing how strongly a pigment absorbs different wavelengths of light.
Ikhadi 294
Umbuzo
What is an action spectrum?
Impendulo
A graph showing the rate or effectiveness of photosynthesis at different wavelengths.
Ikhadi 295
Umbuzo
Which term describes light-driven synthesis of organic molecules from carbon dioxide?
Impendulo
photosynthesis
Ikhadi 296
Umbuzo
Which term describes the principal green photosynthetic pigment?
Impendulo
chlorophyll
Ikhadi 297
Umbuzo
Which term describes a graph of pigment absorption versus wavelength?
Impendulo
an absorption spectrum
Ikhadi 298
Umbuzo
Which term describes a graph of photosynthetic effectiveness versus wavelength?
Impendulo
an action spectrum
Ikhadi 299
Umbuzo
What is photolysis of water?
Impendulo
Light-driven splitting of water that supplies electrons and hydrogen ions and releases oxygen.
Ikhadi 300
Umbuzo
What are light-dependent reactions?
Impendulo
Photosynthetic reactions that use light to generate ATP and reduced electron carriers while releasing oxygen.
Ikhadi 301
Umbuzo
What is the Calvin cycle?
Impendulo
A set of chloroplast reactions that uses ATP and reduced electron carriers to convert carbon dioxide into carbohydrate precursors.
Ikhadi 302
Umbuzo
What is carbon fixation?
Impendulo
Incorporation of inorganic carbon dioxide into an organic molecule.
Ikhadi 303
Umbuzo
Which term describes light-driven splitting of water?
Impendulo
photolysis of water
Ikhadi 304
Umbuzo
Which term describes photosynthetic reactions that directly capture light energy?
Impendulo
light-dependent reactions
Ikhadi 305
Umbuzo
Which term describes the carbon-reduction cycle of photosynthesis?
Impendulo
the Calvin cycle
Ikhadi 306
Umbuzo
Which term describes incorporation of carbon dioxide into organic matter?
Impendulo
carbon fixation
Ikhadi 307
Umbuzo
What is the role of a stoma in photosynthesis?
Impendulo
A pore in the leaf epidermis that regulates carbon-dioxide entry as well as water loss.
Ikhadi 308
Umbuzo
What is a limiting factor of photosynthesis?
Impendulo
The environmental factor whose availability currently restricts the photosynthetic rate.
Ikhadi 309
Umbuzo
What is the light compensation point?
Impendulo
The light intensity at which photosynthetic carbon uptake equals respiratory carbon release.
Ikhadi 310
Umbuzo
What is the overall word equation for oxygenic photosynthesis?
Impendulo
Carbon dioxide + water → carbohydrate + oxygen, using light energy.
Ikhadi 311
Umbuzo
Which term describes the regulated leaf pore controlling carbon-dioxide entry for photosynthesis?
Impendulo
a stoma
Ikhadi 312
Umbuzo
Which term describes the factor currently restricting photosynthetic rate?
Impendulo
a limiting factor
Ikhadi 313
Umbuzo
Which term describes the light level where photosynthesis and respiration balance?
Impendulo
the light compensation point
Ikhadi 314
Umbuzo
Where do the main stages of photosynthesis occur in a chloroplast?
Impendulo
Light-dependent reactions occur in thylakoid membranes; carbon-fixation reactions occur in the stroma.
Ikhadi 315
Umbuzo
What energy conversion occurs during photosynthesis?
Impendulo
Light energy is converted into chemical energy stored first in ATP and reduced carriers and ultimately in organic molecules.
Ikhadi 316
Umbuzo
From which reactant does the oxygen released by photosynthesis originate?
Impendulo
Water.
Ikhadi 317
Umbuzo
What role does RuBisCO play in photosynthesis?
Impendulo
It catalyzes fixation of carbon dioxide by adding it to an organic acceptor molecule.
Ikhadi 318
Umbuzo
What tradeoff is controlled when stomata open?
Impendulo
Opening permits carbon dioxide entry but increases water loss by transpiration.
Ikhadi 319
Umbuzo
Name three leaf features that support photosynthesis.
Impendulo
A broad surface captures light, a thin structure shortens diffusion paths, and veins supply water and remove sugars; chloroplast-rich cells and stomata also help.
Ikhadi 320
Umbuzo
What can a plant do with carbohydrate made by photosynthesis?
Impendulo
Use it in respiration, convert it to storage or structural carbohydrates, or use its carbon to make lipids, amino acids, and other molecules.
Ikhadi 321
Umbuzo
How are products of the light-dependent reactions used in carbon fixation?
Impendulo
ATP supplies energy and NADPH supplies reducing power for conversion of fixed carbon into carbohydrate precursors.
Ikhadi 322
Umbuzo
Why does increasing light intensity eventually stop increasing photosynthetic rate?
Impendulo
Another factor, such as carbon dioxide supply, temperature, or biochemical capacity, becomes limiting.
Ikhadi 323
Umbuzo
How can increasing carbon dioxide concentration affect photosynthetic rate?
Impendulo
It can increase the rate until another factor becomes limiting.
Ikhadi 324
Umbuzo
Why does photosynthetic rate usually have a temperature optimum?
Impendulo
Enzyme-controlled reactions accelerate with temperature up to an optimum, then decline as enzymes and membranes lose effective function.
Ikhadi 325
Umbuzo
Why does an action spectrum broadly resemble the combined absorption spectra of photosynthetic pigments?
Impendulo
Wavelengths absorbed by the pigments supply more energy for photosynthesis than poorly absorbed wavelengths.
Ikhadi 326
Umbuzo
What is semiconservative replication?
Impendulo
DNA replication in which each daughter molecule contains one parental strand and one newly synthesized strand.
Ikhadi 327
Umbuzo
What is DNA helicase?
Impendulo
An enzyme that unwinds the double helix and separates the strands by disrupting base pairing.
Ikhadi 328
Umbuzo
What is DNA polymerase?
Impendulo
An enzyme that adds nucleotides to a growing DNA strand using a template.
Ikhadi 329
Umbuzo
What is a primer?
Impendulo
A short nucleic-acid segment providing a free 3′ end from which DNA polymerase can extend.
Ikhadi 330
Umbuzo
Which term describes replication producing one old and one new strand per DNA molecule?
Impendulo
semiconservative replication
Ikhadi 331
Umbuzo
Which term describes the enzyme that separates DNA strands?
Impendulo
DNA helicase
Ikhadi 332
Umbuzo
Which term describes the enzyme that builds DNA from a template?
Impendulo
DNA polymerase
Ikhadi 333
Umbuzo
Which term describes the short segment providing a starting 3′ end?
Impendulo
a primer
Ikhadi 334
Umbuzo
What is the leading strand?
Impendulo
The new DNA strand synthesized continuously toward the replication fork.
Ikhadi 335
Umbuzo
What is the lagging strand?
Impendulo
The new DNA strand synthesized discontinuously away from the replication fork.
Ikhadi 336
Umbuzo
What is an Okazaki fragment?
Impendulo
A short DNA segment synthesized on the lagging strand.
Ikhadi 337
Umbuzo
What is DNA ligase?
Impendulo
An enzyme that seals breaks in the sugar-phosphate backbone, joining DNA fragments.
Ikhadi 338
Umbuzo
Which term describes the continuously synthesized daughter strand?
Impendulo
the leading strand
Ikhadi 339
Umbuzo
Which term describes the discontinuously synthesized daughter strand?
Impendulo
the lagging strand
Ikhadi 340
Umbuzo
Which term describes a short newly made segment of lagging-strand DNA?
Impendulo
an Okazaki fragment
Ikhadi 341
Umbuzo
Which term describes the enzyme that joins DNA fragments by sealing the backbone?
Impendulo
DNA ligase
Ikhadi 342
Umbuzo
How does complementary base pairing ensure accurate DNA copying?
Impendulo
Each template base specifies the nucleotide added opposite it: A pairs with T, and C pairs with G.
Ikhadi 343
Umbuzo
Why does DNA polymerase synthesize DNA only 5′ to 3′?
Impendulo
It can add a nucleotide only to the free 3′ hydroxyl group of the growing strand.
Ikhadi 344
Umbuzo
When in the cell cycle is nuclear DNA replicated?
Impendulo
During S phase of interphase, before cell division.
Ikhadi 345
Umbuzo
How can a replication error become a permanent mutation?
Impendulo
If it escapes proofreading and repair, the altered sequence can be copied in later cell generations.
Ikhadi 346
Umbuzo
Why are leading and lagging strands synthesized differently?
Impendulo
The templates are antiparallel while DNA polymerase works only 5′ to 3′, forcing one strand to be made discontinuously.
Ikhadi 347
Umbuzo
How do proofreading and repair reduce replication errors?
Impendulo
Incorrectly paired nucleotides are recognized, removed, and replaced before or after replication continues.
Ikhadi 348
Umbuzo
What three repeating steps amplify DNA in PCR?
Impendulo
Strand separation by heating, primer annealing during cooling, and DNA extension by a heat-stable polymerase.
Ikhadi 349
Umbuzo
What determines which DNA region PCR amplifies?
Impendulo
The sequences and positions of the two primers flanking the target region.
Ikhadi 350
Umbuzo
What is transcription?
Impendulo
Synthesis of RNA from a DNA template.
Ikhadi 351
Umbuzo
What is RNA polymerase?
Impendulo
The enzyme that synthesizes RNA complementary to a DNA template strand.
Ikhadi 352
Umbuzo
What is messenger RNA?
Impendulo
RNA carrying a coding sequence from DNA to ribosomes.
Ikhadi 353
Umbuzo
What is a codon?
Impendulo
A three-base sequence in mRNA that specifies an amino acid or a translation signal.
Ikhadi 354
Umbuzo
Which term describes RNA synthesis from DNA?
Impendulo
transcription
Ikhadi 355
Umbuzo
Which term describes the enzyme that builds RNA from a DNA template?
Impendulo
RNA polymerase
Ikhadi 356
Umbuzo
Which term describes RNA that carries coding information to ribosomes?
Impendulo
messenger RNA
Ikhadi 357
Umbuzo
Which term describes a three-base mRNA unit?
Impendulo
a codon
Ikhadi 358
Umbuzo
What is translation?
Impendulo
Synthesis of a polypeptide using the codon sequence of mRNA.
Ikhadi 359
Umbuzo
What does a ribosome do during translation?
Impendulo
It reads mRNA and catalyzes polypeptide synthesis using its rRNA-protein machinery.
Ikhadi 360
Umbuzo
What is transfer RNA?
Impendulo
RNA that carries a specific amino acid and pairs its anticodon with an mRNA codon.
Ikhadi 361
Umbuzo
What is an anticodon?
Impendulo
A three-base tRNA sequence complementary to an mRNA codon.
Ikhadi 362
Umbuzo
Which term describes polypeptide synthesis from an mRNA sequence?
Impendulo
translation
Ikhadi 363
Umbuzo
Which term describes the translation complex that reads mRNA and builds a polypeptide?
Impendulo
a ribosome
Ikhadi 364
Umbuzo
Which term describes the adaptor RNA carrying an amino acid?
Impendulo
transfer RNA
Ikhadi 365
Umbuzo
Which term describes the tRNA triplet that pairs with a codon?
Impendulo
an anticodon
Ikhadi 366
Umbuzo
What is the genetic code?
Impendulo
The set of rules relating mRNA codons to amino acids and translation signals.
Ikhadi 367
Umbuzo
What are start and stop codons?
Impendulo
mRNA signals that establish the reading frame or terminate translation.
Ikhadi 368
Umbuzo
Where do transcription and translation occur in a eukaryotic cell?
Impendulo
Transcription occurs in the nucleus; translation occurs on ribosomes in the cytoplasm or on rough ER.
Ikhadi 369
Umbuzo
How is an mRNA sequence related to its DNA template strand?
Impendulo
It is complementary and antiparallel, with uracil in RNA opposite adenine in DNA.
Ikhadi 370
Umbuzo
Which term describes the codon-to-amino-acid rule set?
Impendulo
the genetic code
Ikhadi 371
Umbuzo
Which term describes codons that begin or end translation?
Impendulo
start and stop codons
Ikhadi 372
Umbuzo
What reaction does the ribosome catalyze as a polypeptide grows?
Impendulo
Formation of peptide bonds between adjacent amino acids.
Ikhadi 373
Umbuzo
What does it mean that the genetic code is degenerate?
Impendulo
Most amino acids are specified by more than one codon.
Ikhadi 374
Umbuzo
How can one mRNA produce many polypeptides quickly?
Impendulo
Multiple ribosomes can translate the same mRNA simultaneously as a polyribosome.
Ikhadi 375
Umbuzo
Why is translation not the final step in producing many functional proteins?
Impendulo
The polypeptide must fold and may undergo cleavage, chemical modification, or assembly with other subunits.
Ikhadi 376
Umbuzo
How does mRNA compare with the DNA coding strand?
Impendulo
It has the same base sequence except that RNA contains uracil where DNA contains thymine.
Ikhadi 377
Umbuzo
What happens during eukaryotic RNA splicing?
Impendulo
Introns are removed and exons are joined to form mature mRNA.
Ikhadi 378
Umbuzo
Why must codons be read in the correct reading frame?
Impendulo
Changing the starting position changes every downstream triplet and therefore the amino-acid sequence.
Ikhadi 379
Umbuzo
How is the correct amino acid matched to each mRNA codon?
Impendulo
Each tRNA is charged with a particular amino acid, and its anticodon pairs with the complementary codon.
Ikhadi 380
Umbuzo
How can a base substitution affect a protein?
Impendulo
It may be silent, change one amino acid, create a stop codon, or sometimes alter RNA processing.
Ikhadi 381
Umbuzo
What is a mutation?
Impendulo
A change in a DNA sequence or chromosome structure that can be passed to daughter cells.
Ikhadi 382
Umbuzo
What is a base substitution?
Impendulo
Replacement of one nucleotide pair by another.
Ikhadi 383
Umbuzo
What is an insertion mutation?
Impendulo
Addition of one or more nucleotides to a DNA sequence.
Ikhadi 384
Umbuzo
What is a deletion mutation?
Impendulo
Loss of one or more nucleotides from a DNA sequence.
Ikhadi 385
Umbuzo
Which term describes a lasting DNA-sequence or chromosome change?
Impendulo
a mutation
Ikhadi 386
Umbuzo
Which term describes replacement of one DNA base pair?
Impendulo
a base substitution
Ikhadi 387
Umbuzo
Which term describes addition of nucleotides to DNA?
Impendulo
an insertion mutation
Ikhadi 388
Umbuzo
Which term describes loss of nucleotides from DNA?
Impendulo
a deletion mutation
Ikhadi 389
Umbuzo
What is a frameshift mutation?
Impendulo
A coding-sequence insertion or deletion not divisible by three that changes downstream codon grouping.
Ikhadi 390
Umbuzo
What is a silent mutation?
Impendulo
A sequence change that does not alter the encoded amino acid.
Ikhadi 391
Umbuzo
What is a missense mutation?
Impendulo
A mutation that changes a codon so a different amino acid is incorporated.
Ikhadi 392
Umbuzo
What is a nonsense mutation?
Impendulo
A mutation that changes an amino-acid codon into a stop codon.
Ikhadi 393
Umbuzo
Which term describes a mutation that shifts downstream codon grouping?
Impendulo
a frameshift mutation
Ikhadi 394
Umbuzo
Which term describes a coding change that leaves the amino acid unchanged?
Impendulo
a silent mutation
Ikhadi 395
Umbuzo
Which term describes a mutation causing one amino-acid substitution?
Impendulo
a missense mutation
Ikhadi 396
Umbuzo
Which term describes a mutation creating a premature stop codon?
Impendulo
a nonsense mutation
Ikhadi 397
Umbuzo
How do germline and somatic mutations differ in inheritance?
Impendulo
Germline mutations can enter gametes and be inherited; somatic mutations affect a cell lineage within the individual.
Ikhadi 398
Umbuzo
What can cause mutations?
Impendulo
Replication errors, spontaneous chemical changes, radiation, and mutagenic chemicals can alter DNA.
Ikhadi 399
Umbuzo
How does DNA repair protect genome stability?
Impendulo
Repair systems detect damaged or mismatched DNA and restore the correct structure or sequence when possible.
Ikhadi 400
Umbuzo
Why are mutations essential to evolution despite often being neutral or harmful?
Impendulo
They create new alleles, providing the heritable variation on which selection and drift act.
Ikhadi 401
Umbuzo
What is the basic role of guide RNA in CRISPR gene editing?
Impendulo
It directs a nuclease to a complementary DNA sequence.
Ikhadi 402
Umbuzo
Why can the same type of DNA mutation have effects ranging from none to severe?
Impendulo
Effects depend on location, genetic-code redundancy, protein role, cell type, and environmental context.
Ikhadi 403
Umbuzo
How can accumulated mutations contribute to cancer?
Impendulo
Mutations can activate growth-promoting genes or disable genes that restrain division, repair DNA, or trigger cell death.
Ikhadi 404
Umbuzo
Why can repairing a CRISPR-induced DNA break produce different editing outcomes?
Impendulo
Different cellular repair pathways may disrupt the target sequence or use a supplied template for a specific change.
Ikhadi 405
Umbuzo
What is an off-target effect in gene editing?
Impendulo
An unintended DNA change at a site sufficiently similar to the intended target.
Ikhadi 406
Umbuzo
Why does heritable human genome editing raise additional ethical concerns?
Impendulo
Changes could pass to future generations who cannot consent, with uncertain long-term biological and social effects.
Ikhadi 407
Umbuzo
What is the cell cycle?
Impendulo
The ordered sequence of cell growth, DNA replication, nuclear division, and cell division.
Ikhadi 408
Umbuzo
What is interphase?
Impendulo
The period of growth, normal activity, and DNA replication between nuclear divisions.
Ikhadi 409
Umbuzo
What is mitosis?
Impendulo
Nuclear division that usually produces genetically equivalent daughter nuclei.
Ikhadi 410
Umbuzo
What is cytokinesis?
Impendulo
Division of the cytoplasm to form separate daughter cells.
Ikhadi 411
Umbuzo
Which term describes the ordered sequence from one cell division to the next?
Impendulo
the cell cycle
Ikhadi 412
Umbuzo
Which term describes the growth and DNA-replication period between divisions?
Impendulo
interphase
Ikhadi 413
Umbuzo
Which term describes division producing genetically equivalent nuclei?
Impendulo
mitosis
Ikhadi 414
Umbuzo
Which term describes physical division of the cytoplasm?
Impendulo
cytokinesis
Ikhadi 415
Umbuzo
What is a chromosome?
Impendulo
One DNA molecule packaged with associated proteins.
Ikhadi 416
Umbuzo
What are sister chromatids?
Impendulo
The two replicated copies of a chromosome joined before separation.
Ikhadi 417
Umbuzo
What is a centromere?
Impendulo
The chromosome region that holds sister chromatids together and organizes kinetochore attachment.
Ikhadi 418
Umbuzo
What is the mitotic spindle?
Impendulo
A microtubule system that attaches to and separates chromosomes during cell division.
Ikhadi 419
Umbuzo
Which term describes a protein-packaged DNA molecule?
Impendulo
a chromosome
Ikhadi 420
Umbuzo
Which term describes joined replicated copies of one chromosome?
Impendulo
sister chromatids
Ikhadi 421
Umbuzo
Which term describes the chromosome region joining sister chromatids?
Impendulo
a centromere
Ikhadi 422
Umbuzo
Which term describes the chromosome-separating microtubule system?
Impendulo
the mitotic spindle
Ikhadi 423
Umbuzo
What is the basic sequence of mitosis?
Impendulo
Chromosomes condense, align at the cell equator, sister chromatids separate to opposite poles, and new nuclei form.
Ikhadi 424
Umbuzo
Why must DNA replicate before mitosis?
Impendulo
Each chromosome must have two copies so each daughter nucleus can receive a complete genome.
Ikhadi 425
Umbuzo
Why are daughter cells from mitosis usually genetically similar?
Impendulo
Replicated sister chromatids are separated so each daughter receives one copy of every chromosome.
Ikhadi 426
Umbuzo
What are major roles of mitosis in multicellular organisms?
Impendulo
Growth, tissue repair, cell replacement, and some forms of asexual reproduction.
Ikhadi 427
Umbuzo
How do homologous chromosomes differ from sister chromatids?
Impendulo
Homologs carry the same gene loci but may have different alleles; sister chromatids are replicated copies of one chromosome.
Ikhadi 428
Umbuzo
What key outcome distinguishes mitosis from meiosis?
Impendulo
Mitosis usually preserves chromosome number and similarity; meiosis halves chromosome number and generates genetically varied haploid cells.
Ikhadi 429
Umbuzo
How does cytokinesis commonly occur in animal cells?
Impendulo
A contractile ring tightens the plasma membrane into a cleavage furrow.
Ikhadi 430
Umbuzo
How does cytokinesis commonly occur in plant cells?
Impendulo
Vesicles fuse at the center to form a cell plate that develops into new membranes and a cell wall.
Ikhadi 431
Umbuzo
What is the purpose of cell-cycle checkpoints?
Impendulo
They delay progression when conditions are unsuitable or DNA and chromosome attachment are defective.
Ikhadi 432
Umbuzo
How is loss of cell-cycle control related to cancer?
Impendulo
Cells can divide despite damage or growth restraints, producing an expanding abnormal clone.
Ikhadi 433
Umbuzo
What is a gene?
Impendulo
A DNA sequence that contributes to a functional product and influences a characteristic or cellular process.
Ikhadi 434
Umbuzo
What is an allele?
Impendulo
One of the alternative DNA-sequence forms at a gene locus.
Ikhadi 435
Umbuzo
What is a gene locus?
Impendulo
The physical position of a gene on a chromosome.
Ikhadi 436
Umbuzo
What is a genotype?
Impendulo
The allele combination of an organism at one or more loci.
Ikhadi 437
Umbuzo
Which term describes a functional DNA sequence?
Impendulo
a gene
Ikhadi 438
Umbuzo
Which term describes an alternative form of a gene?
Impendulo
an allele
Ikhadi 439
Umbuzo
Which term describes a gene's chromosome position?
Impendulo
a gene locus
Ikhadi 440
Umbuzo
Which term describes an organism's allele combination?
Impendulo
a genotype
Ikhadi 441
Umbuzo
What is a phenotype?
Impendulo
An observable or measurable trait produced by genotype and environment.
Ikhadi 442
Umbuzo
What is homozygous?
Impendulo
Having two identical alleles at a diploid locus.
Ikhadi 443
Umbuzo
What is heterozygous?
Impendulo
Having two different alleles at a diploid locus.
Ikhadi 444
Umbuzo
What is a dominant allele?
Impendulo
An allele expressed in the phenotype of a heterozygote under a specified inheritance model.
Ikhadi 445
Umbuzo
Which term describes an observable trait resulting from genes and environment?
Impendulo
a phenotype
Ikhadi 446
Umbuzo
Which term describes having two identical alleles at a locus?
Impendulo
homozygous
Ikhadi 447
Umbuzo
Which term describes having two different alleles at a locus?
Impendulo
heterozygous
Ikhadi 448
Umbuzo
Which term describes an allele expressed in a heterozygote?
Impendulo
a dominant allele
Ikhadi 449
Umbuzo
What is a recessive allele?
Impendulo
An allele whose phenotype is masked by a dominant allele in a heterozygote.
Ikhadi 450
Umbuzo
What is a genetic carrier?
Impendulo
An unaffected heterozygote who can transmit a recessive disease allele.
Ikhadi 451
Umbuzo
What is a test cross?
Impendulo
A cross with a homozygous recessive individual used to infer an unknown dominant phenotype's genotype.
Ikhadi 452
Umbuzo
What is a pedigree?
Impendulo
A diagram showing biological relationships and occurrence of a trait across generations.
Ikhadi 453
Umbuzo
Which term describes an allele masked in a heterozygote?
Impendulo
a recessive allele
Ikhadi 454
Umbuzo
Which term describes an unaffected heterozygote carrying a recessive disease allele?
Impendulo
a genetic carrier
Ikhadi 455
Umbuzo
Which term describes a cross used to reveal an unknown dominant genotype?
Impendulo
a test cross
Ikhadi 456
Umbuzo
Which term describes a family diagram tracking a trait across generations?
Impendulo
a pedigree
Ikhadi 457
Umbuzo
What does allele segregation mean during gamete formation?
Impendulo
The two alleles at a diploid locus separate so each gamete receives one.
Ikhadi 458
Umbuzo
What does a Punnett square predict?
Impendulo
Expected genotype and phenotype probabilities from specified parental gametes, not guaranteed family outcomes.
Ikhadi 459
Umbuzo
What phenotypic ratio is expected from Aa × Aa with complete dominance?
Impendulo
Approximately 3 dominant phenotype : 1 recessive phenotype.
Ikhadi 460
Umbuzo
What genotypic ratio is expected from Aa × Aa?
Impendulo
1 AA : 2 Aa : 1 aa.
Ikhadi 461
Umbuzo
What happens in codominance?
Impendulo
Both alleles contribute distinctly to the heterozygous phenotype.
Ikhadi 462
Umbuzo
What happens in incomplete dominance?
Impendulo
The heterozygote has a phenotype intermediate between the two homozygotes.
Ikhadi 463
Umbuzo
How can environment affect phenotype without changing genotype?
Impendulo
Conditions alter development, physiology, or gene expression, changing the observed trait.
Ikhadi 464
Umbuzo
What is the ultimate source of new alleles?
Impendulo
Mutation.
Ikhadi 465
Umbuzo
Why are X-linked recessive traits more common in XY individuals?
Impendulo
They have only one X chromosome, so one recessive allele on it can determine the phenotype.
Ikhadi 466
Umbuzo
When is the product rule used in genetic probability?
Impendulo
For independent events that must both occur; multiply their probabilities.
Ikhadi 467
Umbuzo
When is the sum rule used in genetic probability?
Impendulo
For mutually exclusive alternative outcomes; add their probabilities.
Ikhadi 468
Umbuzo
Why do polygenic traits often show continuous variation?
Impendulo
Many loci contribute small effects, creating many possible genotypes and phenotypes, often further influenced by environment.
Ikhadi 469
Umbuzo
What pedigree pattern can suggest an autosomal recessive trait?
Impendulo
Unaffected parents can have affected children, and all sexes are affected at similar frequencies.
Ikhadi 470
Umbuzo
What is a species?
Impendulo
A group of organisms whose members can potentially interbreed and produce fertile offspring under natural conditions.
Ikhadi 471
Umbuzo
What is binomial nomenclature?
Impendulo
The two-part scientific naming system using a genus name followed by a specific epithet.
Ikhadi 472
Umbuzo
What is taxonomy?
Impendulo
The naming and classification of organisms.
Ikhadi 473
Umbuzo
What is a biological domain?
Impendulo
The broadest commonly used taxonomic rank, separating Bacteria, Archaea, and Eukarya.
Ikhadi 474
Umbuzo
Which term describes a naturally interbreeding group producing fertile offspring?
Impendulo
a species
Ikhadi 475
Umbuzo
Which term describes the genus-plus-specific-epithet naming system?
Impendulo
binomial nomenclature
Ikhadi 476
Umbuzo
Which term describes the science of naming and classifying organisms?
Impendulo
taxonomy
Ikhadi 477
Umbuzo
Which term describes the broadest common taxonomic rank?
Impendulo
a biological domain
Ikhadi 478
Umbuzo
What is biodiversity?
Impendulo
Variation of life at genetic, species, and ecosystem levels.
Ikhadi 479
Umbuzo
What is an autotroph?
Impendulo
An organism that makes organic compounds from inorganic carbon using light or chemical energy.
Ikhadi 480
Umbuzo
What is a heterotroph?
Impendulo
An organism that obtains organic carbon by consuming other organisms or their products.
amakhadi angu-960
IB Biology SL Flashcards: Complete Course Review
Funda leli qoqo mahhalaI-Nibomo iyavuleka ukuze uqale ukufunda.
Ikhadi 481
Umbuzo
What is a unicellular organism?
Impendulo
An organism consisting of one cell that carries out all essential life functions.
Ikhadi 482
Umbuzo
Which term describes variation of life across genes, species, and ecosystems?
Impendulo
biodiversity
Ikhadi 483
Umbuzo
Which term describes an organism that builds organic matter from inorganic carbon?
Impendulo
an autotroph
Ikhadi 484
Umbuzo
Which term describes an organism obtaining organic carbon from other organisms?
Impendulo
a heterotroph
Ikhadi 485
Umbuzo
Which term describes an organism made of one cell?
Impendulo
a unicellular organism
Ikhadi 486
Umbuzo
What is a multicellular organism?
Impendulo
An organism composed of many cooperating cells, often with specialized cell types.
Ikhadi 487
Umbuzo
What is a karyotype?
Impendulo
An ordered display of chromosomes used to examine their number and large-scale structure.
Ikhadi 488
Umbuzo
What broad feature distinguishes both Bacteria and Archaea from Eukarya?
Impendulo
Their cells lack a nucleus and other membrane-bound organelles.
Ikhadi 489
Umbuzo
What features characterize most plant cells?
Impendulo
Cellulose walls, chloroplasts in photosynthetic tissues, and large vacuoles are typical features.
Ikhadi 490
Umbuzo
Which term describes an organism made of many cooperating cells?
Impendulo
a multicellular organism
Ikhadi 491
Umbuzo
Which term describes an ordered display of an individual's chromosomes?
Impendulo
a karyotype
Ikhadi 492
Umbuzo
How do fungi obtain nutrients?
Impendulo
They secrete digestive enzymes and absorb soluble products; their cells usually have chitin-containing walls.
Ikhadi 493
Umbuzo
What distinguishes animal nutrition and cell structure?
Impendulo
Animals ingest organic material, and their cells lack cell walls and chloroplasts.
Ikhadi 494
Umbuzo
Why are scientific names useful across languages?
Impendulo
A standardized name identifies the same organism internationally and reduces ambiguity from local common names.
Ikhadi 495
Umbuzo
Why can genetic diversity improve a population's resilience?
Impendulo
More heritable variation increases the chance that some individuals tolerate new diseases or environmental changes.
Ikhadi 496
Umbuzo
What does ecosystem diversity measure?
Impendulo
The variety of habitats, communities, and ecological processes within a region.
Ikhadi 497
Umbuzo
Why are Archaea classified separately from Bacteria?
Impendulo
They differ in genetic sequences, membrane chemistry, cell-wall composition, and aspects of molecular machinery.
Ikhadi 498
Umbuzo
Why is the biological species concept difficult to apply to fossils or asexual organisms?
Impendulo
Their ability to interbreed and produce fertile offspring cannot be tested in the usual way.
Ikhadi 499
Umbuzo
Does a larger chromosome number necessarily mean a more complex organism?
Impendulo
No. Chromosome number varies through fusion, fission, and duplication and does not directly measure biological complexity.
Ikhadi 500
Umbuzo
Does genome size reliably predict organismal complexity?
Impendulo
No. Large amounts of noncoding and repeated DNA make genome size a poor simple measure of complexity.
Ikhadi 501
Umbuzo
What evidence can be combined when classifying organisms?
Impendulo
Molecular sequences, cell structure, anatomy, development, physiology, and reproductive evidence can all contribute.
Ikhadi 502
Umbuzo
What is gas exchange?
Impendulo
Diffusion of respiratory gases between an organism and its environment or transport fluid.
Ikhadi 503
Umbuzo
What is ventilation?
Impendulo
Bulk movement of air or water over a gas-exchange surface.
Ikhadi 504
Umbuzo
What is an alveolus?
Impendulo
A microscopic air sac in the lung where gases diffuse between air and blood.
Ikhadi 505
Umbuzo
What is pulmonary surfactant?
Impendulo
A substance lining alveoli that lowers surface tension and reduces collapse.
Ikhadi 506
Umbuzo
Which term describes diffusion of oxygen and carbon dioxide across a respiratory surface?
Impendulo
gas exchange
Ikhadi 507
Umbuzo
Which term describes bulk movement of respiratory medium over an exchange surface?
Impendulo
ventilation
Ikhadi 508
Umbuzo
Which term describes a microscopic lung air sac?
Impendulo
an alveolus
Ikhadi 509
Umbuzo
Which term describes the alveolar lining that lowers surface tension?
Impendulo
pulmonary surfactant
Ikhadi 510
Umbuzo
What is the diaphragm?
Impendulo
A sheet of skeletal muscle whose contraction increases thoracic volume during inhalation.
Ikhadi 511
Umbuzo
What is tidal volume?
Impendulo
The volume of air moved in or out during a normal breath.
Ikhadi 512
Umbuzo
What is a stoma?
Impendulo
A regulated epidermal pore through which gases diffuse in leaves.
Ikhadi 513
Umbuzo
What is countercurrent exchange?
Impendulo
Exchange between fluids moving in opposite directions, maintaining a gradient along most of the surface.
Ikhadi 514
Umbuzo
Which term describes the muscle sheet that expands the thorax during inhalation?
Impendulo
the diaphragm
Ikhadi 515
Umbuzo
Which term describes air volume moved in one normal breath?
Impendulo
tidal volume
Ikhadi 516
Umbuzo
Which term describes a regulated leaf gas-exchange pore?
Impendulo
a stoma
Ikhadi 517
Umbuzo
Which term describes opposite fluid flow that maintains an exchange gradient?
Impendulo
countercurrent exchange
Ikhadi 518
Umbuzo
What features make an efficient gas-exchange surface?
Impendulo
Large area, short diffusion distance, permeability, and maintained concentration gradients.
Ikhadi 519
Umbuzo
How is a steep oxygen gradient maintained across alveoli?
Impendulo
Ventilation replenishes alveolar oxygen and blood flow removes absorbed oxygen.
Ikhadi 520
Umbuzo
How does diaphragm contraction cause inhalation?
Impendulo
Thoracic volume increases, lung pressure falls below atmospheric pressure, and air flows inward.
Ikhadi 521
Umbuzo
What drives quiet exhalation?
Impendulo
The diaphragm relaxes and elastic recoil reduces thoracic and lung volume, raising pressure and pushing air out.
Ikhadi 522
Umbuzo
Why do ventilation rate and depth increase during exercise?
Impendulo
They increase oxygen uptake and carbon dioxide removal to support higher cellular respiration.
Ikhadi 523
Umbuzo
How does leaf structure shorten the pathway for carbon dioxide diffusion?
Impendulo
Stomata open into air spaces, and mesophyll cells expose moist surfaces close to those spaces.
Ikhadi 524
Umbuzo
Why does carbon dioxide diffuse from tissues into blood?
Impendulo
Respiring cells produce carbon dioxide, making its partial pressure higher in tissues than in incoming blood.
Ikhadi 525
Umbuzo
How does countercurrent flow improve oxygen uptake at fish gills?
Impendulo
Blood continually meets water with a higher oxygen concentration, preserving diffusion along the lamella.
Ikhadi 526
Umbuzo
Why does closing stomata reduce both water loss and photosynthesis?
Impendulo
It limits water-vapor diffusion out but also restricts carbon dioxide diffusion into the leaf.
Ikhadi 527
Umbuzo
What is a circulatory system?
Impendulo
A transport system that moves a fluid carrying gases, nutrients, wastes, hormones, and heat through an organism.
Ikhadi 528
Umbuzo
What is an artery?
Impendulo
A blood vessel carrying blood away from the heart under relatively high pressure.
Ikhadi 529
Umbuzo
What is a vein?
Impendulo
A blood vessel carrying blood toward the heart, usually with low pressure and often valves.
Ikhadi 530
Umbuzo
What is a capillary?
Impendulo
A microscopic thin-walled vessel where substances exchange between blood and tissues.
Ikhadi 531
Umbuzo
Which term describes an internal fluid-transport system?
Impendulo
a circulatory system
Ikhadi 532
Umbuzo
Which term describes a vessel carrying blood away from the heart?
Impendulo
an artery
Ikhadi 533
Umbuzo
Which term describes a vessel carrying blood toward the heart?
Impendulo
a vein
Ikhadi 534
Umbuzo
Which term describes a microscopic exchange blood vessel?
Impendulo
a capillary
Ikhadi 535
Umbuzo
What is the cardiac cycle?
Impendulo
The repeating sequence of heart-chamber contraction and relaxation that pumps blood.
Ikhadi 536
Umbuzo
What is hemoglobin?
Impendulo
An iron-containing protein in red blood cells that binds oxygen reversibly.
Ikhadi 537
Umbuzo
What is xylem?
Impendulo
Plant vascular tissue that transports water and mineral ions and provides structural support.
Ikhadi 538
Umbuzo
What is phloem?
Impendulo
Plant vascular tissue that transports sucrose and other organic solutes between sources and sinks.
Ikhadi 539
Umbuzo
Which term describes the repeating pumping sequence of the heart?
Impendulo
the cardiac cycle
Ikhadi 540
Umbuzo
Which term describes the oxygen-carrying protein of red blood cells?
Impendulo
hemoglobin
Ikhadi 541
Umbuzo
Which term describes plant tissue carrying water and minerals?
Impendulo
xylem
Ikhadi 542
Umbuzo
Which term describes plant tissue carrying organic solutes?
Impendulo
phloem
Ikhadi 543
Umbuzo
What is transpiration?
Impendulo
Loss of water vapor from plant surfaces, mainly through stomata.
Ikhadi 544
Umbuzo
What is phloem translocation?
Impendulo
Movement of organic solutes through phloem from sources to sinks.
Ikhadi 545
Umbuzo
How do a source and a sink differ in plant transport?
Impendulo
A source releases assimilates to phloem; a sink removes them for use or storage.
Ikhadi 546
Umbuzo
What makes human circulation a double circulation?
Impendulo
Blood passes through the heart once in the pulmonary circuit and again in the systemic circuit during one complete journey.
Ikhadi 547
Umbuzo
Which term describes water-vapor loss from plant surfaces?
Impendulo
transpiration
Ikhadi 548
Umbuzo
Which term describes movement of organic solutes through phloem?
Impendulo
phloem translocation
Ikhadi 549
Umbuzo
Which term describes the exporting and importing regions of phloem transport?
Impendulo
source and sink
Ikhadi 550
Umbuzo
How is an artery adapted to high pressure?
Impendulo
It has thick elastic and muscular walls and a relatively narrow lumen.
Ikhadi 551
Umbuzo
How is a vein adapted to return low-pressure blood?
Impendulo
It has a wide lumen, thinner walls, and valves that reduce backflow.
Ikhadi 552
Umbuzo
How does capillary structure support exchange?
Impendulo
One-cell-thick walls give a short diffusion distance; extensive branching gives a large total area; narrow lumens slow flow and keep blood close to tissues.
Ikhadi 553
Umbuzo
What determines whether a heart valve opens or closes?
Impendulo
Pressure differences across the valve.
Ikhadi 554
Umbuzo
Trace water from soil to the atmosphere through a plant.
Impendulo
Soil → root hairs → root tissues → xylem → leaf mesophyll → leaf air spaces → stomata → atmosphere.
Ikhadi 555
Umbuzo
Why may root cells use active transport to absorb mineral ions?
Impendulo
Ion concentrations can be lower in soil than in root cells, so uptake must occur against a gradient.
Ikhadi 556
Umbuzo
Why do large multicellular organisms need bulk transport systems?
Impendulo
Their low surface-area-to-volume ratio and long diffusion distances make diffusion alone too slow for whole-body supply.
Ikhadi 557
Umbuzo
Why does hemoglobin unload more oxygen in actively respiring tissues?
Impendulo
Lower oxygen and often higher carbon dioxide and acidity reduce hemoglobin's oxygen affinity.
Ikhadi 558
Umbuzo
How does transpiration pull water upward through xylem?
Impendulo
Evaporation lowers leaf water potential and creates tension; cohesion transmits the pull through the continuous water column.
Ikhadi 559
Umbuzo
How do wind and low humidity generally affect transpiration?
Impendulo
Both maintain a steep water-vapor gradient outside the leaf, increasing transpiration if stomata remain open.
Ikhadi 560
Umbuzo
What drives mass flow in phloem?
Impendulo
Sugar loading draws in water and raises pressure at a source; unloading lowers pressure at a sink, producing bulk flow.
Ikhadi 561
Umbuzo
Can the same plant organ be a source at one time and a sink at another?
Impendulo
Yes. A storage organ may import sugars while filling and export them later during growth or germination.
Ikhadi 562
Umbuzo
What is a neuron?
Impendulo
An excitable cell specialized to receive, process, and transmit information.
Ikhadi 563
Umbuzo
What is a sensory neuron?
Impendulo
A neuron carrying information from a receptor toward the central nervous system.
Ikhadi 564
Umbuzo
What is a motor neuron?
Impendulo
A neuron carrying commands from the central nervous system to an effector.
Ikhadi 565
Umbuzo
What is the resting potential?
Impendulo
The voltage difference across an unstimulated neuron's membrane, with the inside negative relative to outside.
Ikhadi 566
Umbuzo
Which term describes an excitable information-transmitting cell?
Impendulo
a neuron
Ikhadi 567
Umbuzo
Which term describes a neuron carrying receptor information to the CNS?
Impendulo
a sensory neuron
Ikhadi 568
Umbuzo
Which term describes a neuron carrying CNS commands to an effector?
Impendulo
a motor neuron
Ikhadi 569
Umbuzo
Which term describes the negative-inside voltage of an unstimulated neuron?
Impendulo
the resting potential
Ikhadi 570
Umbuzo
What is an action potential?
Impendulo
A brief, self-propagating reversal and restoration of membrane potential along an excitable membrane.
Ikhadi 571
Umbuzo
What is depolarization?
Impendulo
A change that makes membrane potential less negative, and during an action potential often positive.
Ikhadi 572
Umbuzo
What is repolarization?
Impendulo
Return of membrane potential toward its resting negative value after depolarization.
Ikhadi 573
Umbuzo
What is a synapse?
Impendulo
A junction where one cell communicates with another cell.
Ikhadi 574
Umbuzo
Which term describes a brief propagating change in neuron membrane voltage?
Impendulo
an action potential
Ikhadi 575
Umbuzo
Which term describes a membrane-voltage change toward a less negative value?
Impendulo
depolarization
Ikhadi 576
Umbuzo
Which term describes return toward resting membrane voltage?
Impendulo
repolarization
Ikhadi 577
Umbuzo
Which term describes a communication junction between cells?
Impendulo
a synapse
Ikhadi 578
Umbuzo
What is a neurotransmitter?
Impendulo
A chemical released by a neuron that changes the activity of a target cell.
Ikhadi 579
Umbuzo
What is the refractory period?
Impendulo
A brief period after an action potential when another is impossible or requires a stronger stimulus.
Ikhadi 580
Umbuzo
What is myelin?
Impendulo
An insulating sheath around some axons that speeds impulse conduction.
Ikhadi 581
Umbuzo
What happens when membrane depolarization reaches threshold?
Impendulo
Voltage-gated channels trigger the self-amplifying events of an action potential.
Ikhadi 582
Umbuzo
Which term describes a neuron-released signaling chemical?
Impendulo
a neurotransmitter
Ikhadi 583
Umbuzo
Which term describes the recovery interval after an action potential?
Impendulo
the refractory period
Ikhadi 584
Umbuzo
Which term describes the insulating axon sheath?
Impendulo
myelin
Ikhadi 585
Umbuzo
What does the all-or-none principle mean for an action potential?
Impendulo
Once threshold is reached, the action potential has a characteristic size; stronger stimuli increase frequency, not its amplitude.
Ikhadi 586
Umbuzo
How does myelin increase conduction speed?
Impendulo
Depolarizing current travels rapidly beneath myelin and action potentials regenerate mainly at gaps in the sheath.
Ikhadi 587
Umbuzo
What is the basic sequence at a chemical synapse?
Impendulo
An impulse triggers neurotransmitter release; it diffuses across the cleft, binds receptors, and alters the postsynaptic cell.
Ikhadi 588
Umbuzo
Why can a reflex response be rapid?
Impendulo
A short neural pathway produces an automatic response without waiting for conscious processing.
Ikhadi 589
Umbuzo
What is sensory transduction?
Impendulo
Conversion of a physical or chemical stimulus into an electrical signal in a receptor cell.
Ikhadi 590
Umbuzo
How does an action potential propagate along an axon?
Impendulo
Local current depolarizes the next membrane region to threshold, opening voltage-gated channels there.
Ikhadi 591
Umbuzo
Why does an action potential normally travel in one direction along an axon?
Impendulo
The membrane just behind it is refractory and cannot immediately fire again.
Ikhadi 592
Umbuzo
How is neurotransmitter action ended?
Impendulo
The transmitter is removed by enzymatic breakdown, reuptake, or diffusion away.
Ikhadi 593
Umbuzo
What is sensory adaptation?
Impendulo
Reduced receptor or neural response during a constant, unchanging stimulus.
Ikhadi 594
Umbuzo
How can a drug alter synaptic transmission?
Impendulo
It may mimic or block a transmitter, change its release, or change its removal from the synaptic cleft.
Ikhadi 595
Umbuzo
What is an organ system?
Impendulo
A group of organs coordinating to perform major functions for an organism.
Ikhadi 596
Umbuzo
What is a hormone?
Impendulo
A signaling molecule released into transport fluid and acting on target cells with suitable receptors.
Ikhadi 597
Umbuzo
What is an endocrine gland?
Impendulo
A gland that secretes hormones into extracellular fluid and blood rather than through a duct.
Ikhadi 598
Umbuzo
What is a hormone target cell?
Impendulo
A cell able to respond because it has the appropriate receptor.
Ikhadi 599
Umbuzo
Which term describes a coordinated group of organs?
Impendulo
an organ system
Ikhadi 600
Umbuzo
Which term describes a long-distance chemical messenger carried in body fluid?
Impendulo
a hormone
Ikhadi 601
Umbuzo
Which term describes a ductless hormone-secreting gland?
Impendulo
an endocrine gland
Ikhadi 602
Umbuzo
Which term describes a cell with a receptor for a particular hormone?
Impendulo
a hormone target cell
Ikhadi 603
Umbuzo
What is digestion?
Impendulo
Mechanical and chemical breakdown of food into molecules small enough to absorb.
Ikhadi 604
Umbuzo
What is absorption?
Impendulo
Movement of digested nutrients across an exchange surface into blood or lymph.
Ikhadi 605
Umbuzo
What is peristalsis?
Impendulo
Coordinated waves of smooth-muscle contraction that move material through the digestive tract.
Ikhadi 606
Umbuzo
What is an intestinal villus?
Impendulo
A finger-like projection increasing the absorptive surface of the small intestine.
Ikhadi 607
Umbuzo
Which term describes breakdown of food into absorbable molecules?
Impendulo
digestion
Ikhadi 608
Umbuzo
Which term describes movement of digested nutrients into transport fluids?
Impendulo
absorption
Ikhadi 609
Umbuzo
Which term describes wave-like gut contractions moving contents?
Impendulo
peristalsis
Ikhadi 610
Umbuzo
Which term describes a finger-like intestinal absorption projection?
Impendulo
an intestinal villus
Ikhadi 611
Umbuzo
What is excretion?
Impendulo
Removal of metabolic waste products from the body.
Ikhadi 612
Umbuzo
What is a nephron?
Impendulo
The microscopic functional unit of the kidney that filters blood and modifies filtrate into urine.
Ikhadi 613
Umbuzo
What is ultrafiltration?
Impendulo
Pressure-driven filtration of small molecules from blood into a kidney capsule while cells and most proteins remain in blood.
Ikhadi 614
Umbuzo
What is selective reabsorption?
Impendulo
Recovery of useful substances and regulated amounts of water and ions from kidney filtrate into blood.
Ikhadi 615
Umbuzo
Which term describes removal of metabolic wastes?
Impendulo
excretion
Ikhadi 616
Umbuzo
Which term describes the kidney's microscopic functional unit?
Impendulo
a nephron
Ikhadi 617
Umbuzo
Which term describes pressure filtration at the start of a nephron?
Impendulo
ultrafiltration
Ikhadi 618
Umbuzo
Which term describes return of useful substances from kidney filtrate to blood?
Impendulo
selective reabsorption
Ikhadi 619
Umbuzo
What is skeletal muscle?
Impendulo
Striated voluntary muscle attached to the skeleton and used for movement and posture.
Ikhadi 620
Umbuzo
What is an antagonistic muscle pair?
Impendulo
Two muscles producing opposite movements at a joint because muscles pull but do not push.
Ikhadi 621
Umbuzo
How do nervous and endocrine signaling generally differ?
Impendulo
Neural signals are rapid and targeted; hormonal signals are usually slower, longer-lasting, and distributed through body fluids.
Ikhadi 622
Umbuzo
Why does a circulating hormone affect only some cells?
Impendulo
Only target cells express receptors that recognize the hormone and activate a response.
Ikhadi 623
Umbuzo
Which term describes voluntary striated muscle that moves the skeleton?
Impendulo
skeletal muscle
Ikhadi 624
Umbuzo
Which term describes two muscles producing opposite joint movements?
Impendulo
an antagonistic muscle pair
Ikhadi 625
Umbuzo
What is the final absorbable product of most dietary carbohydrate digestion?
Impendulo
Monosaccharides, especially glucose.
Ikhadi 626
Umbuzo
What are the main absorbable products of protein digestion?
Impendulo
Amino acids and small peptides that are completed to amino acids during absorption.
Ikhadi 627
Umbuzo
How is the small intestine adapted for absorption?
Impendulo
Folds, villi, and microvilli increase area; a thin epithelium, rich blood supply, and lymph vessels support transport.
Ikhadi 628
Umbuzo
Name three integrative roles of the liver.
Impendulo
It processes absorbed nutrients, regulates blood chemistry, detoxifies substances, produces bile, and converts ammonia to urea; any three are sufficient.
Ikhadi 629
Umbuzo
Why are blood cells and most plasma proteins absent from normal kidney filtrate?
Impendulo
They are too large to cross the filtration barrier.
Ikhadi 630
Umbuzo
How do muscles move a bone at a joint?
Impendulo
Contraction shortens the muscle, pulling through a tendon on the bone.
Ikhadi 631
Umbuzo
Why are antagonistic muscles needed at many joints?
Impendulo
A muscle can pull in one direction but cannot push itself back, so an opposing muscle produces the reverse movement.
Ikhadi 632
Umbuzo
Why must organ systems be integrated rather than acting independently?
Impendulo
Each system depends on materials, signals, waste removal, and stable conditions supplied by other systems.
Ikhadi 633
Umbuzo
Why do many absorbed lipids enter lymph before blood?
Impendulo
Intestinal cells package them into lipoprotein particles too large to enter ordinary blood capillaries directly.
Ikhadi 634
Umbuzo
Why is glucose normally absent from final urine?
Impendulo
Filtered glucose is selectively reabsorbed into blood when transporter capacity is not exceeded.
Ikhadi 635
Umbuzo
How do respiratory, circulatory, and muscular systems cooperate during exercise?
Impendulo
Ventilation supplies oxygen, circulation transports gases and fuels, and muscles use ATP while returning carbon dioxide, heat, and metabolites.
Ikhadi 636
Umbuzo
How do liver, circulation, and kidneys cooperate in nitrogen-waste removal?
Impendulo
The liver converts toxic ammonia to urea, blood carries urea, and kidneys filter and excrete it.
Ikhadi 637
Umbuzo
What is a pathogen?
Impendulo
A biological agent capable of causing disease.
Ikhadi 638
Umbuzo
What is an antigen?
Impendulo
A molecule recognized specifically by an antibody or lymphocyte receptor.
Ikhadi 639
Umbuzo
What is innate immunity?
Impendulo
Rapid, nonspecific defense mechanisms present without prior exposure.
Ikhadi 640
Umbuzo
What is adaptive immunity?
Impendulo
Specific defense that develops through lymphocyte activation and can form memory.
Ikhadi 641
Umbuzo
Which term describes a disease-causing biological agent?
Impendulo
a pathogen
Ikhadi 642
Umbuzo
Which term describes a molecule specifically recognized by adaptive immune receptors?
Impendulo
an antigen
Ikhadi 643
Umbuzo
Which term describes rapid nonspecific immune defense?
Impendulo
innate immunity
Ikhadi 644
Umbuzo
Which term describes specific immune defense capable of memory?
Impendulo
adaptive immunity
Ikhadi 645
Umbuzo
What is a phagocyte?
Impendulo
A cell that engulfs and digests microbes, particles, or damaged cells.
Ikhadi 646
Umbuzo
What is a lymphocyte?
Impendulo
An adaptive immune cell with receptors specific to particular antigens.
Ikhadi 647
Umbuzo
What is an antibody?
Impendulo
A secreted immunoglobulin that binds a specific antigen.
Ikhadi 648
Umbuzo
What is a B lymphocyte?
Impendulo
A lymphocyte that can differentiate into antibody-secreting plasma cells and memory cells.
Ikhadi 649
Umbuzo
Which term describes an engulfing immune cell?
Impendulo
a phagocyte
Ikhadi 650
Umbuzo
Which term describes an antigen-specific adaptive immune cell?
Impendulo
a lymphocyte
Ikhadi 651
Umbuzo
Which term describes a secreted antigen-binding immunoglobulin?
Impendulo
an antibody
Ikhadi 652
Umbuzo
Which term describes the lymphocyte lineage that produces antibody-secreting cells?
Impendulo
a B lymphocyte
Ikhadi 653
Umbuzo
What is a helper T cell?
Impendulo
A lymphocyte that coordinates immune responses through contact signals and cytokines.
Ikhadi 654
Umbuzo
What is an immune memory cell?
Impendulo
A long-lived lymphocyte that responds rapidly after re-exposure to its antigen.
Ikhadi 655
Umbuzo
What is vaccination?
Impendulo
Deliberate exposure to a safe form or component of an antigen to generate protective immune memory.
Ikhadi 656
Umbuzo
What is an antibiotic?
Impendulo
A substance that kills bacteria or inhibits their growth at clinically useful doses.
Ikhadi 657
Umbuzo
Which term describes the T cell that coordinates other immune cells?
Impendulo
a helper T cell
Ikhadi 658
Umbuzo
Which term describes a long-lived lymphocyte enabling faster re-exposure response?
Impendulo
an immune memory cell
Ikhadi 659
Umbuzo
Which term describes safe antigen exposure used to create immune memory?
Impendulo
vaccination
Ikhadi 660
Umbuzo
Which term describes a drug acting against bacteria?
Impendulo
an antibiotic
Ikhadi 661
Umbuzo
What are examples of first-line defenses against pathogens?
Impendulo
Intact skin, mucus, cilia, antimicrobial secretions, stomach acidity, and competing microbiota.
Ikhadi 662
Umbuzo
How does inflammation help defend damaged tissue?
Impendulo
It increases local blood flow and vessel permeability and recruits immune cells and defensive molecules.
Ikhadi 663
Umbuzo
What happens during phagocytosis?
Impendulo
A cell surrounds a particle in a vesicle, then fuses it with digestive compartments to destroy or process it.
Ikhadi 664
Umbuzo
How can antibodies help eliminate a pathogen?
Impendulo
They can neutralize targets, block attachment, clump particles, and mark them for phagocytosis or complement attack.
Ikhadi 665
Umbuzo
Why can a vaccine generate protection without causing the full disease?
Impendulo
It presents antigen in a weakened, inactivated, partial, or encoded form that stimulates immunity with much lower risk.
Ikhadi 666
Umbuzo
Why do antibiotics not treat viral infections?
Impendulo
Viruses lack the bacterial structures and independent metabolic processes targeted by antibiotics.
Ikhadi 667
Umbuzo
What determines the antigen specificity of a lymphocyte?
Impendulo
The molecular shape and chemistry of its unique surface receptor.
Ikhadi 668
Umbuzo
What is clonal selection?
Impendulo
An antigen activates lymphocytes with matching receptors, causing them to proliferate and differentiate.
Ikhadi 669
Umbuzo
Why is a secondary adaptive immune response usually faster and stronger?
Impendulo
Memory cells are more numerous and activate rapidly, producing effective cells and antibodies sooner.
Ikhadi 670
Umbuzo
How can high vaccination coverage protect some unvaccinated people?
Impendulo
Reduced transmission makes encounters with infectious individuals less likely, though protection is incomplete and pathogen-dependent.
Ikhadi 671
Umbuzo
How does antibiotic use select for resistant bacteria?
Impendulo
Susceptible bacteria are removed while resistant variants survive and reproduce, increasing resistance-allele frequency.
Ikhadi 672
Umbuzo
Why can unnecessary or incomplete antibiotic exposure promote resistance?
Impendulo
It creates selection favoring resistant cells while potentially leaving surviving bacteria to multiply and spread.
Ikhadi 673
Umbuzo
What is an allergy?
Impendulo
An immune response to a normally harmless antigen that causes tissue symptoms or damage.
Ikhadi 674
Umbuzo
What is asexual reproduction?
Impendulo
Production of offspring from one parent without fusion of gametes.
Ikhadi 675
Umbuzo
What is sexual reproduction?
Impendulo
Production of offspring involving fusion of haploid gametes.
Ikhadi 676
Umbuzo
What is a gamete?
Impendulo
A haploid reproductive cell able to fuse with another gamete.
Ikhadi 677
Umbuzo
What is fertilization?
Impendulo
Fusion of gamete nuclei to form a diploid zygote.
Ikhadi 678
Umbuzo
Which term describes reproduction without gamete fusion?
Impendulo
asexual reproduction
Ikhadi 679
Umbuzo
Which term describes reproduction involving gamete fusion?
Impendulo
sexual reproduction
Ikhadi 680
Umbuzo
Which term describes a haploid reproductive cell?
Impendulo
a gamete
Ikhadi 681
Umbuzo
Which term describes fusion of gamete nuclei?
Impendulo
fertilization
Ikhadi 682
Umbuzo
What is a zygote?
Impendulo
The diploid cell formed by fertilization.
Ikhadi 683
Umbuzo
What is meiosis?
Impendulo
Cell division that halves chromosome number and usually produces genetically varied haploid cells.
Ikhadi 684
Umbuzo
What is ovulation?
Impendulo
Release of a secondary oocyte from an ovary.
Ikhadi 685
Umbuzo
What is implantation?
Impendulo
Attachment and embedding of an early embryo in the uterine lining.
Ikhadi 686
Umbuzo
Which term describes the first diploid cell after fertilization?
Impendulo
a zygote
Ikhadi 687
Umbuzo
Which term describes division producing varied haploid cells?
Impendulo
meiosis
Ikhadi 688
Umbuzo
Which term describes release of an oocyte from an ovary?
Impendulo
ovulation
Ikhadi 689
Umbuzo
Which term describes embedding of an early embryo in the uterine lining?
Impendulo
implantation
Ikhadi 690
Umbuzo
What is the placenta?
Impendulo
A temporary organ that exchanges materials between maternal and fetal blood supplies without normally mixing them directly.
Ikhadi 691
Umbuzo
What is pollination?
Impendulo
Transfer of pollen from an anther to a receptive stigma.
Ikhadi 692
Umbuzo
Why does sexual reproduction usually produce more genetic variation than asexual reproduction?
Impendulo
Meiosis reshuffles alleles and random fertilization combines genomes from two gametes.
Ikhadi 693
Umbuzo
Why must gametes be haploid?
Impendulo
Fusion of two haploid gametes restores the diploid chromosome number instead of doubling it each generation.
Ikhadi 694
Umbuzo
Which term describes the maternal-fetal exchange organ?
Impendulo
the placenta
Ikhadi 695
Umbuzo
Which term describes transfer of pollen to a stigma?
Impendulo
pollination
Ikhadi 696
Umbuzo
What are major roles of FSH in the ovarian cycle?
Impendulo
It stimulates follicle development and supports estrogen secretion.
Ikhadi 697
Umbuzo
What is a major role of the mid-cycle LH surge?
Impendulo
It triggers ovulation and formation of the corpus luteum.
Ikhadi 698
Umbuzo
How does estrogen contribute to the uterine cycle?
Impendulo
It promotes repair and thickening of the uterine lining after menstruation.
Ikhadi 699
Umbuzo
How does progesterone contribute to the uterine cycle?
Impendulo
It maintains a thick, secretory uterine lining after ovulation.
Ikhadi 700
Umbuzo
Where does human fertilization usually occur?
Impendulo
In an oviduct, before the early embryo reaches the uterus.
Ikhadi 701
Umbuzo
What happens after compatible pollen reaches a flower's stigma?
Impendulo
A pollen tube grows toward an ovule and delivers male nuclei for fertilization.
Ikhadi 702
Umbuzo
Why does menstruation usually begin if pregnancy does not occur?
Impendulo
The corpus luteum degenerates, progesterone and estrogen fall, and the uterine lining is no longer maintained.
Ikhadi 703
Umbuzo
What substances commonly cross the placenta between mother and fetus?
Impendulo
Oxygen and nutrients move toward the fetus; carbon dioxide and nitrogenous wastes move toward the mother.
Ikhadi 704
Umbuzo
How can contraception prevent pregnancy in different ways?
Impendulo
Methods can inhibit ovulation, block sperm from reaching an egg, prevent fertilization, or permanently interrupt the reproductive ducts.
Ikhadi 705
Umbuzo
What is homeostasis?
Impendulo
Maintenance of internal conditions within ranges compatible with normal function despite change.
Ikhadi 706
Umbuzo
What is negative feedback?
Impendulo
Control in which a deviation triggers responses that oppose the original change.
Ikhadi 707
Umbuzo
What is a set point?
Impendulo
The target value or range around which a regulated variable is maintained.
Ikhadi 708
Umbuzo
What is a homeostatic receptor?
Impendulo
A sensor that detects a change in a regulated variable.
Ikhadi 709
Umbuzo
Which term describes maintenance of a stable functional internal environment?
Impendulo
homeostasis
Ikhadi 710
Umbuzo
Which term describes feedback that counteracts a deviation?
Impendulo
negative feedback
Ikhadi 711
Umbuzo
Which term describes the target around which a variable is regulated?
Impendulo
a set point
Ikhadi 712
Umbuzo
Which term describes the sensor in a feedback system?
Impendulo
a homeostatic receptor
Ikhadi 713
Umbuzo
What is a control center?
Impendulo
The component that compares information with a target and coordinates a response.
Ikhadi 714
Umbuzo
What is an effector?
Impendulo
A muscle, gland, or other component that carries out a control response.
Ikhadi 715
Umbuzo
What is thermoregulation?
Impendulo
Control of body temperature within a functional range.
Ikhadi 716
Umbuzo
What is vasodilation?
Impendulo
Widening of blood vessels, often increasing blood flow near the skin.
Ikhadi 717
Umbuzo
Which term describes the feedback component that evaluates input and directs a response?
Impendulo
a control center
Ikhadi 718
Umbuzo
Which term describes the component that executes a physiological response?
Impendulo
an effector
Ikhadi 719
Umbuzo
Which term describes physiological regulation of body temperature?
Impendulo
thermoregulation
Ikhadi 720
Umbuzo
Which term describes widening of blood vessels?
Impendulo
vasodilation
Ikhadi 721
Umbuzo
What is vasoconstriction?
Impendulo
Narrowing of blood vessels, often reducing blood flow near the skin.
Ikhadi 722
Umbuzo
What is insulin?
Impendulo
A pancreatic hormone that lowers elevated blood glucose by promoting uptake and storage.
Ikhadi 723
Umbuzo
What is glucagon?
Impendulo
A pancreatic hormone that raises low blood glucose by promoting release of stored fuel.
Ikhadi 724
Umbuzo
What are the main components of a homeostatic feedback loop?
Impendulo
A regulated variable, receptor, control center, effectors, and responses that alter the variable.
Ikhadi 725
Umbuzo
Which term describes narrowing of blood vessels?
Impendulo
vasoconstriction
Ikhadi 726
Umbuzo
Which term describes the pancreatic hormone that lowers blood glucose?
Impendulo
insulin
Ikhadi 727
Umbuzo
Which term describes the pancreatic hormone that raises blood glucose?
Impendulo
glucagon
Ikhadi 728
Umbuzo
What happens when blood glucose rises after a meal?
Impendulo
Insulin secretion increases, promoting glucose uptake and storage so blood glucose falls toward its normal range.
Ikhadi 729
Umbuzo
What happens when blood glucose falls during fasting?
Impendulo
Glucagon secretion increases, promoting glycogen breakdown and glucose release by the liver.
Ikhadi 730
Umbuzo
How does sweating cool the body?
Impendulo
Evaporation of water from skin transfers heat to the environment.
Ikhadi 731
Umbuzo
How does skin vasodilation increase heat loss?
Impendulo
It brings more warm blood near the surface, increasing transfer of heat to the environment.
Ikhadi 732
Umbuzo
How does shivering warm the body?
Impendulo
Rapid involuntary muscle contractions increase respiration and heat production.
Ikhadi 733
Umbuzo
Does homeostasis keep internal conditions perfectly constant?
Impendulo
No. Variables fluctuate within controlled ranges around target values.
Ikhadi 734
Umbuzo
How does ADH help conserve water?
Impendulo
It increases water permeability in kidney collecting ducts, so more water is reabsorbed and urine becomes more concentrated.
Ikhadi 735
Umbuzo
How should ADH secretion change during dehydration?
Impendulo
It should increase, promoting greater water reabsorption by the kidneys.
Ikhadi 736
Umbuzo
How does positive feedback differ from negative feedback?
Impendulo
Positive feedback amplifies a change until an endpoint; negative feedback opposes a change and stabilizes a variable.
Ikhadi 737
Umbuzo
Why can diabetes mellitus cause persistently high blood glucose?
Impendulo
Insulin production may be insufficient or target cells may respond poorly to insulin.
Ikhadi 738
Umbuzo
What is biological evolution?
Impendulo
Change in heritable characteristics or allele frequencies of a population across generations.
Ikhadi 739
Umbuzo
What is allele frequency?
Impendulo
The proportion of gene copies in a population represented by a particular allele.
Ikhadi 740
Umbuzo
What is microevolution?
Impendulo
Evolutionary change in allele frequencies within populations over relatively short timescales.
Ikhadi 741
Umbuzo
What is speciation?
Impendulo
Evolutionary formation of new species.
Ikhadi 742
Umbuzo
Which term describes change in a population's heritable composition across generations?
Impendulo
biological evolution
Ikhadi 743
Umbuzo
Which term describes the proportion of a population's gene copies that are one allele?
Impendulo
allele frequency
Ikhadi 744
Umbuzo
Which term describes short-timescale allele-frequency change within populations?
Impendulo
microevolution
Ikhadi 745
Umbuzo
Which term describes formation of new species?
Impendulo
speciation
Ikhadi 746
Umbuzo
What is reproductive isolation?
Impendulo
Barriers that prevent or greatly reduce gene flow between populations.
Ikhadi 747
Umbuzo
What is allopatric speciation?
Impendulo
Speciation after populations become geographically separated and diverge.
Ikhadi 748
Umbuzo
What is sympatric speciation?
Impendulo
Speciation without geographic separation, through reproductive isolation within the same area.
Ikhadi 749
Umbuzo
What are homologous structures?
Impendulo
Structures similar because they were inherited from a common ancestor, even if their functions differ.
Ikhadi 750
Umbuzo
Which term describes barriers reducing gene flow between populations?
Impendulo
reproductive isolation
Ikhadi 751
Umbuzo
Which term describes speciation following geographic separation?
Impendulo
allopatric speciation
Ikhadi 752
Umbuzo
Which term describes speciation within the same geographic area?
Impendulo
sympatric speciation
Ikhadi 753
Umbuzo
Which term describes structures similar through common ancestry?
Impendulo
homologous structures
Ikhadi 754
Umbuzo
What are analogous structures?
Impendulo
Structures with similar functions that evolved independently rather than from the same ancestral structure.
Ikhadi 755
Umbuzo
What is a common ancestor?
Impendulo
An ancestral population from which two or more descendant lineages evolved.
Ikhadi 756
Umbuzo
How does the fossil record provide evidence for evolution?
Impendulo
It documents organisms from different times, including appearance, change, persistence, and extinction of lineages.
Ikhadi 757
Umbuzo
How do DNA and protein sequences provide evidence of common ancestry?
Impendulo
Shared sequences are inherited; greater similarity generally indicates more recent common ancestry.
Ikhadi 758
Umbuzo
Which term describes functionally similar structures of independent evolutionary origin?
Impendulo
analogous structures
Ikhadi 759
Umbuzo
Which term describes an ancestral population shared by descendant lineages?
Impendulo
a common ancestor
Ikhadi 760
Umbuzo
What is the evolutionary significance of extinction?
Impendulo
It permanently ends a lineage and can alter ecological opportunities and the future diversification of survivors.
Ikhadi 761
Umbuzo
Do individual organisms evolve during their lifetimes?
Impendulo
No. Individuals develop and acclimate; evolution is heritable change in populations across generations.
Ikhadi 762
Umbuzo
Why is evolution represented as a branching tree rather than a ladder?
Impendulo
Lineages split from common ancestors; living species are not arranged as stages toward a single goal.
Ikhadi 763
Umbuzo
How can island species support evolutionary explanations?
Impendulo
Their similarities to nearby mainland ancestors and unique local adaptations fit divergence after colonization and isolation.
Ikhadi 764
Umbuzo
How can geographic isolation lead to reproductive isolation?
Impendulo
Separated populations accumulate different mutations and experience different selection and drift until interbreeding is reduced.
Ikhadi 765
Umbuzo
Why can continuing gene flow slow speciation?
Impendulo
Movement of alleles between populations counteracts genetic divergence.
Ikhadi 766
Umbuzo
Why can unrelated species evolve similar traits?
Impendulo
Similar environmental challenges can favor similar functional solutions through convergent evolution.
Ikhadi 767
Umbuzo
Which parts of evolution are random and which are nonrandom?
Impendulo
Mutation and many sampling effects are random with respect to need; natural selection nonrandomly favors variants that reproduce better in a given environment.
Ikhadi 768
Umbuzo
What is conservation biology?
Impendulo
The science and practice of protecting biodiversity, ecological processes, and evolutionary potential.
Ikhadi 769
Umbuzo
What is habitat fragmentation?
Impendulo
Division of continuous habitat into smaller, isolated patches.
Ikhadi 770
Umbuzo
What is an endangered species?
Impendulo
A species facing a high risk of extinction in the wild.
Ikhadi 771
Umbuzo
What is in situ conservation?
Impendulo
Protection of species in their natural habitats and ecological communities.
Ikhadi 772
Umbuzo
Which term describes the protection of biodiversity and ecological processes?
Impendulo
conservation biology
Ikhadi 773
Umbuzo
Which term describes division of habitat into isolated patches?
Impendulo
habitat fragmentation
Ikhadi 774
Umbuzo
Which term describes a species at high risk of extinction?
Impendulo
an endangered species
Ikhadi 775
Umbuzo
Which term describes conservation within natural habitat?
Impendulo
in situ conservation
Ikhadi 776
Umbuzo
What is ex situ conservation?
Impendulo
Protection of organisms or genetic material outside the natural habitat.
Ikhadi 777
Umbuzo
What is a population bottleneck?
Impendulo
A sharp population reduction that can remove genetic variation by chance.
Ikhadi 778
Umbuzo
What is a wildlife corridor?
Impendulo
Habitat connecting isolated patches to permit movement and gene flow.
Ikhadi 779
Umbuzo
What major human-driven processes threaten biodiversity?
Impendulo
Habitat loss, overexploitation, invasive species, pollution, and climate change.
Ikhadi 780
Umbuzo
Which term describes conservation outside natural habitat?
Impendulo
ex situ conservation
Ikhadi 781
Umbuzo
Which term describes a severe population reduction that loses genetic diversity?
Impendulo
a population bottleneck
Ikhadi 782
Umbuzo
Which term describes habitat linking isolated populations?
Impendulo
a wildlife corridor
Ikhadi 783
Umbuzo
What makes a protected area more effective than a boundary alone?
Impendulo
Adequate size, representative habitat, enforcement, connectivity, local support, and management of external threats.
Ikhadi 784
Umbuzo
Why is long-term population monitoring important in conservation?
Impendulo
It reveals trends, tests whether management works, and provides early warning of decline.
Ikhadi 785
Umbuzo
How can ecosystem services support the case for conservation?
Impendulo
Healthy ecosystems provide benefits such as pollination, water purification, carbon storage, soil formation, and cultural value.
Ikhadi 786
Umbuzo
Why are very small populations especially vulnerable to extinction?
Impendulo
Chance events, inbreeding, low genetic diversity, and difficulty finding mates can reinforce decline.
Ikhadi 787
Umbuzo
What are benefits and limits of captive-breeding programs?
Impendulo
They can prevent immediate extinction and manage breeding, but may lose diversity, alter behavior, and fail without safe habitat for release.
Ikhadi 788
Umbuzo
Why can controlling an invasive species aid conservation?
Impendulo
It can reduce predation, competition, disease, or habitat alteration affecting native species.
Ikhadi 789
Umbuzo
Why must conservation priorities consider more than species count?
Impendulo
Endemism, evolutionary distinctness, ecological roles, threat severity, feasibility, and human needs also matter.
Ikhadi 790
Umbuzo
What is an adaptation?
Impendulo
A heritable characteristic that increases reproductive success in a particular environment.
Ikhadi 791
Umbuzo
What is acclimation?
Impendulo
A reversible physiological or behavioral adjustment by an individual to environmental change.
Ikhadi 792
Umbuzo
What is a structural adaptation?
Impendulo
An inherited anatomical feature that improves performance in an environment.
Ikhadi 793
Umbuzo
What is a physiological adaptation?
Impendulo
An inherited functional or biochemical feature that improves performance in an environment.
Ikhadi 794
Umbuzo
Which term describes a heritable trait improving reproductive success in context?
Impendulo
an adaptation
Ikhadi 795
Umbuzo
Which term describes an individual's reversible adjustment to environmental change?
Impendulo
acclimation
Ikhadi 796
Umbuzo
Which term describes an adaptive anatomical feature?
Impendulo
a structural adaptation
Ikhadi 797
Umbuzo
Which term describes an adaptive functional or biochemical feature?
Impendulo
a physiological adaptation
Ikhadi 798
Umbuzo
What is a behavioral adaptation?
Impendulo
An inherited behavior pattern that improves survival or reproduction.
Ikhadi 799
Umbuzo
What is an environmental tolerance range?
Impendulo
The range of an abiotic condition within which an organism can survive and reproduce.
Ikhadi 800
Umbuzo
What is evolutionary fitness?
Impendulo
Relative contribution of an individual or genotype to future generations.
Ikhadi 801
Umbuzo
How can a thick cuticle and reduced leaves help a desert plant?
Impendulo
The cuticle lowers surface permeability, while smaller leaves reduce the area from which water can evaporate.
Ikhadi 802
Umbuzo
Which term describes an adaptive behavior pattern?
Impendulo
a behavioral adaptation
Ikhadi 803
Umbuzo
Which term describes the survivable range of an abiotic condition?
Impendulo
an environmental tolerance range
Ikhadi 804
Umbuzo
Which term describes relative reproductive contribution to future generations?
Impendulo
evolutionary fitness
Ikhadi 805
Umbuzo
How can a streamlined body adapt an aquatic animal to movement?
Impendulo
It reduces drag, lowering the energy needed to move through water.
Ikhadi 806
Umbuzo
Does an organism develop an adaptation because it needs one?
Impendulo
No. Heritable variants arise without regard to need, and selection changes their frequencies across generations.
Ikhadi 807
Umbuzo
Why may organisms from different thermal environments have enzymes with different temperature optima?
Impendulo
Selection favors protein structures that balance flexibility and stability under local temperatures.
Ikhadi 808
Umbuzo
Why is an adaptation rarely beneficial in every environment?
Impendulo
Traits carry costs and their advantage depends on local resources, competitors, predators, and physical conditions.
Ikhadi 809
Umbuzo
How does phenotypic plasticity differ from genetic adaptation?
Impendulo
Plasticity lets one genotype produce different phenotypes; adaptation is a heritable population trait shaped across generations.
Ikhadi 810
Umbuzo
What is local adaptation?
Impendulo
A population has higher fitness in its home environment than foreign populations because selection favored local traits.
Ikhadi 811
Umbuzo
What is an ecological niche?
Impendulo
The set of environmental conditions, resources, interactions, and functional roles associated with a species.
Ikhadi 812
Umbuzo
What is a habitat?
Impendulo
The physical place or environment where an organism lives.
Ikhadi 813
Umbuzo
What is a fundamental niche?
Impendulo
The full range of conditions and resources a species could use without limiting biotic interactions.
Ikhadi 814
Umbuzo
What is a realized niche?
Impendulo
The conditions and resources a species actually uses after competition and other interactions.
Ikhadi 815
Umbuzo
Which term describes a species' environmental requirements and ecological role?
Impendulo
an ecological niche
Ikhadi 816
Umbuzo
Which term describes the place where an organism lives?
Impendulo
a habitat
Ikhadi 817
Umbuzo
Which term describes the potential niche without limiting biotic interactions?
Impendulo
a fundamental niche
Ikhadi 818
Umbuzo
Which term describes the niche actually occupied in nature?
Impendulo
a realized niche
Ikhadi 819
Umbuzo
What is competition?
Impendulo
An interaction in which organisms reduce one another's access to a limited resource.
Ikhadi 820
Umbuzo
What is mutualism?
Impendulo
An interaction in which both participating species benefit.
Ikhadi 821
Umbuzo
What is predation?
Impendulo
An interaction in which one organism kills and consumes another.
Ikhadi 822
Umbuzo
How does a habitat differ from a niche?
Impendulo
A habitat is where an organism lives; a niche includes how it uses conditions and resources and interacts there.
Ikhadi 823
Umbuzo
Which term describes an interaction over a limited resource that harms both competitors?
Impendulo
competition
Ikhadi 824
Umbuzo
Which term describes an interspecific interaction benefiting both partners?
Impendulo
mutualism
Ikhadi 825
Umbuzo
Which term describes an interaction where one organism kills and eats another?
Impendulo
predation
Ikhadi 826
Umbuzo
What kinds of factors define a niche?
Impendulo
Abiotic factors such as temperature and moisture, plus biotic factors such as food, competitors, predators, and partners.
Ikhadi 827
Umbuzo
What does competitive exclusion predict?
Impendulo
Species with effectively identical niches cannot coexist indefinitely under stable conditions; one is excluded or niches diverge.
Ikhadi 828
Umbuzo
How can resource partitioning reduce competition?
Impendulo
Species use different resources, places, or times, reducing niche overlap.
Ikhadi 829
Umbuzo
What is a keystone species?
Impendulo
A species whose effect on community structure is disproportionately large relative to its abundance.
Ikhadi 830
Umbuzo
Why can an introduced species expand rapidly in a new community?
Impendulo
It may encounter abundant resources, suitable climate, and fewer predators, pathogens, or competitors.
Ikhadi 831
Umbuzo
Can an organism alter the niche conditions of other species?
Impendulo
Yes. Ecosystem engineers modify habitat structure or resource availability, changing opportunities for other organisms.
Ikhadi 832
Umbuzo
What is a population?
Impendulo
Individuals of the same species living in the same area at the same time.
Ikhadi 833
Umbuzo
What is an ecological community?
Impendulo
Populations of different species living and interacting in an area.
Ikhadi 834
Umbuzo
What is an ecosystem?
Impendulo
A community together with its physical environment and their interactions.
Ikhadi 835
Umbuzo
What is carrying capacity?
Impendulo
The population size an environment can sustain over time under given conditions.
Ikhadi 836
Umbuzo
Which term describes same-species individuals sharing an area and time?
Impendulo
a population
Ikhadi 837
Umbuzo
Which term describes interacting populations of different species?
Impendulo
an ecological community
Ikhadi 838
Umbuzo
Which term describes a community plus its abiotic environment?
Impendulo
an ecosystem
Ikhadi 839
Umbuzo
Which term describes the long-term supportable population size?
Impendulo
carrying capacity
Ikhadi 840
Umbuzo
What is population density?
Impendulo
The number of individuals per unit area or volume.
Ikhadi 841
Umbuzo
What is a limiting factor?
Impendulo
A resource or condition that restricts population growth or distribution.
Ikhadi 842
Umbuzo
What is a density-dependent factor?
Impendulo
A factor whose effect strengthens as population density increases.
Ikhadi 843
Umbuzo
What is a density-independent factor?
Impendulo
A factor whose effect is not primarily determined by population density.
Ikhadi 844
Umbuzo
Which term describes individuals per unit area or volume?
Impendulo
population density
Ikhadi 845
Umbuzo
Which term describes a resource or condition restricting a population?
Impendulo
a limiting factor
Ikhadi 846
Umbuzo
Which term describes a factor with stronger effects at higher density?
Impendulo
a density-dependent factor
Ikhadi 847
Umbuzo
Which term describes a factor acting largely regardless of population density?
Impendulo
a density-independent factor
Ikhadi 848
Umbuzo
What is exponential population growth?
Impendulo
Growth at a constant per-capita rate, producing a J-shaped curve under ideal conditions.
Ikhadi 849
Umbuzo
What is logistic population growth?
Impendulo
Growth that slows as population size approaches carrying capacity, producing an S-shaped model.
Ikhadi 850
Umbuzo
What four processes directly change population size?
Impendulo
Births and immigration increase it; deaths and emigration decrease it.
Ikhadi 851
Umbuzo
Under what conditions can exponential growth occur temporarily?
Impendulo
Resources are abundant and limiting effects such as competition, disease, and predation are weak.
Ikhadi 852
Umbuzo
Which term describes J-shaped growth at constant per-capita rate?
Impendulo
exponential population growth
Ikhadi 853
Umbuzo
Which term describes S-shaped growth that slows near carrying capacity?
Impendulo
logistic population growth
Ikhadi 854
Umbuzo
Why is infectious disease often density dependent?
Impendulo
Close or frequent contact at high density increases transmission opportunities.
Ikhadi 855
Umbuzo
Give an example of a density-independent population factor.
Impendulo
A severe storm, wildfire, drought, or freeze can affect populations regardless of their initial density.
Ikhadi 856
Umbuzo
When is quadrat sampling useful?
Impendulo
For estimating abundance or frequency of sessile or slow-moving organisms in defined areas.
Ikhadi 857
Umbuzo
What can a transect reveal?
Impendulo
How species occurrence or abundance changes along an environmental gradient.
Ikhadi 858
Umbuzo
What can happen when a population overshoots carrying capacity?
Impendulo
Resource depletion may raise mortality or lower reproduction, causing decline or oscillation.
Ikhadi 859
Umbuzo
What is the basic mark–recapture estimate of population size?
Impendulo
First sample marked × second sample total ÷ marked individuals recaptured.
Ikhadi 860
Umbuzo
What assumptions improve a mark–recapture estimate?
Impendulo
Marks persist and do not affect survival, marked individuals mix, capture probability is similar, and the population is effectively closed.
Ikhadi 861
Umbuzo
Why does a correlation between two population variables not prove causation?
Impendulo
A third factor, reverse influence, chance, or biased sampling could produce the association.
Ikhadi 862
Umbuzo
What is a trophic level?
Impendulo
A feeding position in a food chain or web.
Ikhadi 863
Umbuzo
What is a producer?
Impendulo
An autotroph that converts inorganic carbon into organic matter.
Ikhadi 864
Umbuzo
What is a consumer?
Impendulo
An organism obtaining energy and matter by eating other organisms or organic material.
Ikhadi 865
Umbuzo
What is a decomposer?
Impendulo
An organism that externally digests dead material and wastes and absorbs the products.
Ikhadi 866
Umbuzo
Which term describes a feeding position in an ecosystem?
Impendulo
a trophic level
Ikhadi 867
Umbuzo
Which term describes an autotroph forming organic matter?
Impendulo
a producer
Ikhadi 868
Umbuzo
Which term describes an organism feeding on other organic matter?
Impendulo
a consumer
Ikhadi 869
Umbuzo
Which term describes an organism digesting dead organic matter externally?
Impendulo
a decomposer
Ikhadi 870
Umbuzo
What is a food chain?
Impendulo
A linear representation of feeding and energy-transfer relationships.
Ikhadi 871
Umbuzo
What is a food web?
Impendulo
A network of interconnected feeding relationships in a community.
Ikhadi 872
Umbuzo
What is gross primary productivity?
Impendulo
The total rate at which producers capture energy into organic matter.
Ikhadi 873
Umbuzo
What is net primary productivity?
Impendulo
Producer energy stored as new biomass after subtracting producer respiration from gross primary productivity.
Ikhadi 874
Umbuzo
Which term describes a linear feeding sequence?
Impendulo
a food chain
Ikhadi 875
Umbuzo
Which term describes a network of connected food chains?
Impendulo
a food web
Ikhadi 876
Umbuzo
Which term describes the total producer energy-capture rate?
Impendulo
gross primary productivity
Ikhadi 877
Umbuzo
Which term describes producer biomass gain after respiration?
Impendulo
net primary productivity
Ikhadi 878
Umbuzo
What is ecological productivity?
Impendulo
The rate of biomass or energy production per unit area or volume.
Ikhadi 879
Umbuzo
What is a biogeochemical cycle?
Impendulo
Movement of an element or compound through organisms and the physical environment.
Ikhadi 880
Umbuzo
Why is less energy available at each higher trophic level?
Impendulo
Not all biomass is eaten or digested, and organisms use energy in respiration, movement, maintenance, and heat loss.
Ikhadi 881
Umbuzo
Why does energy flow rather than cycle through an ecosystem?
Impendulo
Energy enters mainly as light and ultimately disperses as heat, which ecosystems cannot fully recycle.
Ikhadi 882
Umbuzo
Which term describes the rate of biomass or energy production?
Impendulo
ecological productivity
Ikhadi 883
Umbuzo
Which term describes cycling of matter through living and nonliving reservoirs?
Impendulo
a biogeochemical cycle
Ikhadi 884
Umbuzo
Why can matter cycle through an ecosystem?
Impendulo
Atoms are conserved and repeatedly transferred among organisms, detritus, soil, water, and atmosphere.
Ikhadi 885
Umbuzo
Why is a pyramid of energy always upright?
Impendulo
Usable energy decreases between trophic levels because every transfer includes losses.
Ikhadi 886
Umbuzo
How are gross and net primary productivity related?
Impendulo
NPP = GPP − producer respiration.
Ikhadi 887
Umbuzo
How do decomposers support nutrient cycling?
Impendulo
They break down dead material and wastes, releasing inorganic nutrients for reuse.
Ikhadi 888
Umbuzo
What processes move carbon rapidly between organisms and the atmosphere?
Impendulo
Photosynthesis removes carbon dioxide; respiration, decomposition, and combustion release it.
Ikhadi 889
Umbuzo
Why is nitrogen fixation important?
Impendulo
It converts atmospheric nitrogen gas into forms that can enter biological nitrogen metabolism.
Ikhadi 890
Umbuzo
How can excess nitrogen or phosphorus cause eutrophication?
Impendulo
Nutrient enrichment drives algal growth; decomposition of the biomass consumes oxygen and can create hypoxic water.
Ikhadi 891
Umbuzo
Why can a persistent pollutant reach higher concentrations at higher trophic levels?
Impendulo
Predators consume contaminant stored in many prey, and the substance is not readily broken down or excreted.
Ikhadi 892
Umbuzo
How is trophic-transfer efficiency calculated?
Impendulo
Energy or biomass gained by the higher trophic level ÷ energy or biomass available at the lower level × 100%.
Ikhadi 893
Umbuzo
What is phenotypic variation?
Impendulo
Differences in observable traits among individuals of a population.
Ikhadi 894
Umbuzo
What is heritable variation?
Impendulo
Trait differences that can be transmitted genetically to offspring.
Ikhadi 895
Umbuzo
What is a selection pressure?
Impendulo
An environmental factor causing differences in survival or reproduction among phenotypes.
Ikhadi 896
Umbuzo
What is relative fitness?
Impendulo
An individual's reproductive success compared with others in the population.
Ikhadi 897
Umbuzo
Which term describes observable differences among individuals?
Impendulo
phenotypic variation
Ikhadi 898
Umbuzo
Which term describes genetically transmissible trait differences?
Impendulo
heritable variation
Ikhadi 899
Umbuzo
Which term describes an environmental factor producing differential reproductive success?
Impendulo
a selection pressure
Ikhadi 900
Umbuzo
Which term describes reproductive success relative to other individuals?
Impendulo
relative fitness
Ikhadi 901
Umbuzo
What is directional selection?
Impendulo
Selection favoring one extreme phenotype and shifting a population's trait distribution.
Ikhadi 902
Umbuzo
What is stabilizing selection?
Impendulo
Selection favoring intermediate phenotypes and acting against extremes.
Ikhadi 903
Umbuzo
What is disruptive selection?
Impendulo
Selection favoring both extreme phenotypes over intermediates.
Ikhadi 904
Umbuzo
What is sexual selection?
Impendulo
Selection arising from differences in mating success.
Ikhadi 905
Umbuzo
Which term describes selection shifting a trait toward one extreme?
Impendulo
directional selection
Ikhadi 906
Umbuzo
Which term describes selection favoring intermediate phenotypes?
Impendulo
stabilizing selection
Ikhadi 907
Umbuzo
Which term describes selection favoring both trait extremes?
Impendulo
disruptive selection
Ikhadi 908
Umbuzo
Which term describes selection caused by unequal mating success?
Impendulo
sexual selection
Ikhadi 909
Umbuzo
What conditions are required for natural selection?
Impendulo
Individuals vary, some variation is heritable, more offspring are produced than can reproduce, and variants differ in reproductive success.
Ikhadi 910
Umbuzo
How does natural selection produce antibiotic-resistant bacterial populations?
Impendulo
Existing resistant variants survive treatment and reproduce more than susceptible bacteria.
Ikhadi 911
Umbuzo
Does an antibiotic cause bacteria to mutate specifically toward resistance?
Impendulo
No. Resistance variants arise without regard to need; treatment selects among them.
Ikhadi 912
Umbuzo
Can an individual become genetically adapted through natural selection?
Impendulo
No. Selection acts on individuals, but adaptation is a population change across generations.
Ikhadi 913
Umbuzo
How does artificial selection differ from natural selection?
Impendulo
Humans choose breeding traits in artificial selection; environmental conditions determine differential reproduction in natural selection.
Ikhadi 914
Umbuzo
How does natural selection change a population?
Impendulo
Individuals with advantageous heritable variants leave more offspring, increasing those alleles over generations.
Ikhadi 915
Umbuzo
Why is fitness environment-dependent?
Impendulo
A trait that improves reproduction in one environment may be neutral or costly in another.
Ikhadi 916
Umbuzo
How does genetic drift differ from natural selection?
Impendulo
Drift changes allele frequencies by chance sampling; selection changes them through consistent fitness differences.
Ikhadi 917
Umbuzo
What is ecosystem stability?
Impendulo
The capacity of an ecosystem to maintain or recover its structure and functions despite disturbance.
Ikhadi 918
Umbuzo
What is an ecological tipping point?
Impendulo
A threshold beyond which feedbacks can drive a large and difficult-to-reverse ecosystem shift.
Ikhadi 919
Umbuzo
What is a mesocosm?
Impendulo
A controlled, simplified ecosystem used to investigate ecological processes under more realistic conditions than a small laboratory vessel.
Ikhadi 920
Umbuzo
What is a sustainable yield?
Impendulo
A harvest rate that can continue without causing long-term resource decline under prevailing conditions.
Ikhadi 921
Umbuzo
Which term describes the capacity of an ecosystem to persist or recover after disturbance?
Impendulo
ecosystem stability
Ikhadi 922
Umbuzo
Which term describes a threshold triggering a major hard-to-reverse ecosystem shift?
Impendulo
an ecological tipping point
Ikhadi 923
Umbuzo
Which term describes a controlled model ecosystem used for experiments?
Impendulo
a mesocosm
Ikhadi 924
Umbuzo
Which term describes a harvest rate that avoids long-term depletion?
Impendulo
a sustainable yield
Ikhadi 925
Umbuzo
What is eutrophication?
Impendulo
Nutrient enrichment of water that stimulates excess primary production and can lead to oxygen depletion.
Ikhadi 926
Umbuzo
What is biomagnification?
Impendulo
Increase in concentration of a persistent pollutant at successively higher trophic levels.
Ikhadi 927
Umbuzo
What is rewilding?
Impendulo
Ecosystem restoration that rebuilds natural processes, species interactions, and self-sustaining ecological function.
Ikhadi 928
Umbuzo
What features can make an ecosystem more stable?
Impendulo
Diverse functional roles, connected habitats, intact food webs, nutrient cycling, and balancing feedbacks can help the system resist or recover from disturbance.
Ikhadi 929
Umbuzo
Which term describes nutrient enrichment that can deplete oxygen in water?
Impendulo
eutrophication
Ikhadi 930
Umbuzo
Which term describes increasing pollutant concentration up a food chain?
Impendulo
biomagnification
Ikhadi 931
Umbuzo
Which term describes restoration focused on natural processes and self-sustaining ecosystems?
Impendulo
rewilding
Ikhadi 932
Umbuzo
How could extensive Amazon deforestation push the ecosystem toward a tipping point?
Impendulo
Loss of trees can reduce rainfall recycling and increase heat and fire, which cause further forest loss and may shift large areas toward a drier state.
Ikhadi 933
Umbuzo
What are a benefit and a limitation of using a mesocosm?
Impendulo
It allows controlled experiments with interacting organisms, but its simplified scale cannot reproduce every process or long-term influence in a natural ecosystem.
Ikhadi 934
Umbuzo
Why should a fishery harvest below an uncertain maximum sustainable yield?
Impendulo
Population estimates and recruitment vary, so a safety margin reduces the chance that error or a poor breeding year drives long-term decline.
Ikhadi 935
Umbuzo
How can intensive agriculture reduce ecosystem stability?
Impendulo
Habitat loss, low crop diversity, soil degradation, heavy water use, pesticides, and nutrient runoff can weaken food webs and ecosystem processes.
Ikhadi 936
Umbuzo
Why can microplastic pollution harm aquatic ecosystems?
Impendulo
Small persistent particles can be ingested, carry additives or other pollutants, damage feeding and tissues, and move through food webs.
Ikhadi 937
Umbuzo
How can rewilding improve ecosystem stability?
Impendulo
Restoring native species, habitat connections, and natural disturbance or grazing processes can rebuild feedbacks and allow the ecosystem to maintain itself with less intervention.
Ikhadi 938
Umbuzo
What is the greenhouse effect?
Impendulo
Warming caused when atmospheric gases absorb and re-emit outgoing infrared radiation.
Ikhadi 939
Umbuzo
What is a greenhouse gas?
Impendulo
An atmospheric gas that absorbs infrared radiation at wavelengths emitted by Earth.
Ikhadi 940
Umbuzo
What is carbon dioxide (CO₂)?
Impendulo
A long-lived greenhouse gas increased mainly by fossil-fuel combustion, cement production, and land-use change.
Ikhadi 941
Umbuzo
What is methane (CH₄)?
Impendulo
A potent greenhouse gas emitted by sources including fossil-fuel systems, livestock, rice cultivation, wetlands, and waste.
Ikhadi 942
Umbuzo
Which term describes warming from absorption and re-emission of infrared radiation?
Impendulo
the greenhouse effect
Ikhadi 943
Umbuzo
Which term describes an atmospheric infrared-absorbing gas?
Impendulo
a greenhouse gas
Ikhadi 944
Umbuzo
Which term describes the long-lived greenhouse gas strongly increased by fossil fuels?
Impendulo
carbon dioxide (CO₂)
Ikhadi 945
Umbuzo
Which term describes the potent short-lived greenhouse gas from biological and fossil sources?
Impendulo
methane (CH₄)
Ikhadi 946
Umbuzo
What is albedo?
Impendulo
The fraction of incoming radiation reflected by a surface.
Ikhadi 947
Umbuzo
What is a carbon sink?
Impendulo
A reservoir that absorbs more carbon than it releases over a specified period.
Ikhadi 948
Umbuzo
What is ocean acidification?
Impendulo
Decline in seawater pH caused mainly by absorption of human-emitted carbon dioxide.
Ikhadi 949
Umbuzo
What is climate change?
Impendulo
A persistent change in the statistical patterns of climate over decades or longer.
Ikhadi 950
Umbuzo
Which term describes surface reflectivity?
Impendulo
albedo
Ikhadi 951
Umbuzo
Which term describes a reservoir with net carbon uptake?
Impendulo
a carbon sink
Ikhadi 952
Umbuzo
Which term describes seawater pH decline from absorbed carbon dioxide?
Impendulo
ocean acidification
Ikhadi 953
Umbuzo
Which term describes long-term change in climate patterns?
Impendulo
climate change
Ikhadi 954
Umbuzo
What is the enhanced greenhouse effect?
Impendulo
Additional warming caused by human-driven increases in greenhouse-gas concentrations.
Ikhadi 955
Umbuzo
How do climate mitigation and climate adaptation differ?
Impendulo
Mitigation limits the magnitude of climate change; adaptation reduces harm from changes that occur.
Ikhadi 956
Umbuzo
How does increasing greenhouse-gas concentration alter Earth's energy balance?
Impendulo
Less outgoing infrared energy initially escapes to space, so the climate warms until energy balance is restored at a higher temperature.
Ikhadi 957
Umbuzo
How can melting ice amplify warming?
Impendulo
Less bright ice lowers albedo, so darker land or water absorbs more solar energy and causes further warming.
Ikhadi 958
Umbuzo
How can climate change alter species distributions?
Impendulo
Temperature, rainfall, seasons, sea level, and interactions shift, moving or shrinking areas with suitable conditions.
Ikhadi 959
Umbuzo
Why can ocean acidification harm calcifying organisms?
Impendulo
Carbonate chemistry changes, reducing availability of carbonate ions used to build calcium-carbonate structures.
Ikhadi 960
Umbuzo
How can ecosystem protection contribute to climate mitigation?
Impendulo
Protecting forests, wetlands, soils, and coastal habitats can avoid emissions and maintain or increase carbon storage.
amakhadi angu-960
IB Biology SL Flashcards: Complete Course Review
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