I85PREP
⌘ K
CAPE Biology Unit 1 study materials
CAPE Biology Unit 1 study resources

CAPE Biology Unit 1 practice questions

One question at a time. Build your CAPE Biology Unit 1 understanding.

First 50 of 195 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Module 1

Which organelle is the principal site of ATP synthesis by oxidative phosphorylation in a eukaryotic cell?

  1. Mitochondrion Correct answer.
  2. Rough endoplasmic reticulum
  3. Golgi apparatus
  4. Lysosome

Explanation

The inner mitochondrial membrane carries the electron transport chain and ATP synthase, so oxidative phosphorylation occurs there. The other organelles listed perform protein processing, modification, or hydrolysis rather than bulk ATP synthesis.

Question 2Module 1

A student views a cell under the light microscope and observes a rigid outer layer lying outside the plasma membrane. Which structure is being described?

  1. Nuclear envelope
  2. Cytoskeleton
  3. Plasmalemma
  4. Cell wall Correct answer.

Explanation

The cell wall is a rigid extracellular layer outside the plasma membrane, giving shape and mechanical support. The nuclear envelope surrounds the nucleus, the cytoskeleton is intracellular, and the plasmalemma is the plasma membrane itself.

Question 3Module 1

Which feature distinguishes prokaryotic cells from eukaryotic cells?

  1. Prokaryotes lack a membrane-bound nucleus Correct answer.
  2. Prokaryotes lack a plasma membrane
  3. Prokaryotes lack ribosomes
  4. Prokaryotes lack nucleic acids

Explanation

Prokaryotes keep their genetic material in a nucleoid region without a nuclear envelope, whereas eukaryotes have a true nucleus. Prokaryotes still possess ribosomes, a plasma membrane, and DNA.

Question 4Module 1

Which statement best describes the fluid mosaic model of membrane structure?

  1. A single layer of phospholipids surrounds a protein core
  2. A rigid protein sheet coats a static lipid layer
  3. Lipids form a solid crystalline barrier with no proteins
  4. Proteins are embedded in or associated with a fluid phospholipid bilayer Correct answer.

Explanation

The model proposes a fluid phospholipid bilayer in which proteins float and are variously embedded or peripheral, giving a mosaic appearance. The bilayer is dynamic, not rigid or crystalline, and proteins are integral to it.

Question 5Module 1

Which process moves water across a selectively permeable membrane from a region of higher water potential to one of lower water potential?

  1. Osmosis Correct answer.
  2. Facilitated diffusion of ions
  3. Active transport
  4. Phagocytosis

Explanation

Osmosis is the passive movement of water down a water potential gradient through a selectively permeable membrane. Active transport requires energy, phagocytosis is engulfment of particles, and ion facilitated diffusion concerns solutes rather than water.

Question 6Module 1

Which substance is the immediate energy currency used directly by most cellular processes?

  1. ATP Correct answer.
  2. Pyruvate
  3. Glucose
  4. NADH

Explanation

ATP hydrolysis releases energy that is coupled directly to endergonic cellular reactions. Glucose and pyruvate are fuel molecules, and NADH is an electron carrier rather than a direct energy currency.

Question 7Module 1

Which property of water allows it to act as an effective solvent for many ionic and polar substances?

  1. Its high surface tension
  2. Its high specific heat capacity
  3. Its polarity Correct answer.
  4. Its low density as a solid

Explanation

Water molecules are polar, so their partial charges attract and surround ions and polar molecules, dissolving them. High specific heat, ice density, and surface tension are important properties but do not explain solvent action.

Question 8Module 1

Which bond forms between the amino group of one amino acid and the carboxyl group of another during protein synthesis?

  1. Peptide bond Correct answer.
  2. Glycosidic bond
  3. Ester bond
  4. Phosphodiester bond

Explanation

A condensation reaction between an amino group and a carboxyl group releases water and forms a peptide bond. Glycosidic bonds join sugars, ester bonds join glycerol and fatty acids, and phosphodiester bonds join nucleotides.

Question 9Module 1

A plant cell with a solute potential of −600 kPa and a pressure potential of +200 kPa is placed in pure water. What is its water potential?

  1. −400 kPa Correct answer.
  2. +400 kPa
  3. −600 kPa
  4. −800 kPa

Explanation

Water potential equals solute potential plus pressure potential, so −600 + 200 = −400 kPa. Pure water at atmospheric pressure has a water potential of zero, so water enters the cell.

Question 10Module 1

An enzyme-catalysed reaction is studied as substrate concentration increases while enzyme concentration is fixed. Which best explains why the rate plateaus at high substrate concentration?

  1. All active sites are occupied so the enzyme is saturated Correct answer.
  2. The enzyme is used up during the reaction
  3. The substrate begins to denature the enzyme
  4. The activation energy of the reaction increases

Explanation

At high substrate concentration every active site is occupied, so the rate is limited by the number of enzyme molecules and reaches a maximum. Enzymes are catalysts and are not consumed, and saturation does not raise activation energy.

Question 11Module 1

A competitive inhibitor is added to an enzyme-catalysed reaction. How does this affect the reaction kinetics?

  1. Maximum rate falls but substrate affinity is unchanged
  2. Both maximum rate and substrate affinity fall
  3. Maximum rate is unchanged but more substrate is needed to reach it Correct answer.
  4. Neither maximum rate nor substrate affinity changes

Explanation

A competitive inhibitor binds the active site and can be outcompeted by raising substrate concentration, so the maximum rate is unchanged while the substrate concentration needed for half-maximal rate increases. Non-competitive inhibition instead lowers the maximum rate.

Question 12Module 1

Which statement correctly describes the role of NAD in respiration?

  1. It is the final electron acceptor at the end of the electron transport chain
  2. It accepts electrons and hydrogen at glycolysis and the Krebs cycle Correct answer.
  3. It transports pyruvate across the inner mitochondrial membrane
  4. It phosphorylates ADP directly during glycolysis

Explanation

NAD is reduced to NADH when it accepts electrons and hydrogen during glycolysis and the Krebs cycle, then delivers them to the electron transport chain. Oxygen, not NAD, is the final electron acceptor.

Question 13Module 1

In the light-dependent reactions of photosynthesis, what is the immediate source of electrons that replace those lost by chlorophyll?

  1. NADPH
  2. Water Correct answer.
  3. Glucose
  4. Carbon dioxide

Explanation

Photolysis of water supplies electrons to the photosystems, releasing oxygen as a by-product. Carbon dioxide is fixed in the light-independent reactions, and NADPH is an electron carrier produced, not a source for photosystem replacement.

Question 14Module 1

Which event occurs during the S phase of the cell cycle?

  1. Chromosome condensation
  2. Spindle formation
  3. DNA replication Correct answer.
  4. Cytokinesis

Explanation

The S phase is the synthesis phase in which DNA is replicated so each chromosome consists of two sister chromatids. Chromosome condensation and spindle formation occur in mitosis, and cytokinesis divides the cytoplasm after mitosis.

Question 15Module 1

During which stage of mitosis do homologous chromosomes separate?

  1. Telophase of mitosis
  2. Anaphase of mitosis
  3. Anaphase I of meiosis, not mitosis Correct answer.
  4. Metaphase of mitosis

Explanation

Homologous chromosomes pair and separate during anaphase I of meiosis; mitosis separates sister chromatids at anaphase. This distinction underlies the halving of chromosome number in meiosis.

Question 16Module 1

A cell with a diploid number of 24 undergoes meiosis. What is the chromosome number in each resulting gamete?

  1. 12 Correct answer.
  2. 48
  3. 6
  4. 24

Explanation

Meiosis halves the chromosome number, so a diploid cell with 24 chromosomes produces gametes with 12 chromosomes each. Doubling would give 48, and 6 would require a further reduction.

Question 17Module 1

Which statement about the genetic code is correct?

  1. It is degenerate because several codons specify the same amino acid Correct answer.
  2. Each codon specifies more than one amino acid
  3. Codons are read in pairs of bases
  4. Each amino acid is coded by exactly one codon

Explanation

The code is degenerate because most amino acids correspond to more than one codon, which reduces the effect of some mutations. It is not ambiguous, so each codon specifies only one amino acid, and codons are triplets.

Question 18Module 1

A mutation changes a single base so that one codon becomes a stop codon. What is the most likely consequence for the polypeptide?

  1. It is unaffected because the code is degenerate
  2. It is lengthened by additional amino acids
  3. It has one amino acid substituted with no other change
  4. It is shortened and may be non-functional Correct answer.

Explanation

A nonsense mutation creates a premature stop codon, so translation terminates early and the polypeptide is truncated, often losing function. Degeneracy protects against some substitutions but not against a codon becoming a stop signal.

Question 19Module 1

In a cross between two heterozygous individuals for a single gene, what phenotypic ratio is expected with complete dominance?

  1. 1:2:1
  2. 3:1 Correct answer.
  3. 9:3:3:1
  4. 1:1

Explanation

A monohybrid cross of two heterozygotes gives a 3:1 phenotypic ratio with complete dominance, though the genotypic ratio is 1:2:1. The 9:3:3:1 ratio arises from a dihybrid cross.

Question 20Module 1

Which feature of the fluid mosaic model explains why small non-polar molecules cross membranes readily while ions do not?

  1. The cholesterol content
  2. The glycoprotein coat
  3. The hydrophobic core of the bilayer Correct answer.
  4. The presence of peripheral proteins

Explanation

The hydrophobic interior of the phospholipid bilayer allows non-polar molecules to dissolve and diffuse through, while charged ions are repelled and need channels. Peripheral proteins and glycoproteins do not provide a general diffusion route for lipids.

Question 21Module 1

Which statement best explains why the rate of diffusion of a gas into a cell increases when the concentration gradient is steeper?

  1. The gas molecules are actively pumped into the cell
  2. The membrane becomes more permeable to the gas
  3. The net movement of molecules down the gradient is greater Correct answer.
  4. The molecules gain activation energy from the membrane

Explanation

Diffusion is driven by a concentration gradient, so a steeper gradient produces a greater net movement of molecules into the cell. It remains passive and does not involve activation energy or active pumping.

Question 22Module 1

An enzyme is placed in a solution at a pH far from its optimum. Which change most directly accounts for the loss of activity?

  1. Competitive inhibitors occupy the active site
  2. The substrate concentration falls below the saturation point
  3. The activation energy of the reaction increases
  4. Ionic and hydrogen bonds maintaining tertiary structure are disrupted Correct answer.

Explanation

Extreme pH alters the ionisation of amino acid side chains, breaking ionic and hydrogen bonds that hold the tertiary structure, so the active site loses its shape. This is a conformational change rather than a change in substrate supply or inhibition.

Question 23Module 1

A potato strip is placed in a concentrated sucrose solution. Which observation is expected and why?

  1. It loses mass because sucrose leaves the cells
  2. It shows no change because the cell wall prevents water movement
  3. It gains mass because sucrose enters the cells
  4. It loses mass because water leaves the cells by osmosis Correct answer.

Explanation

The external solution has a lower water potential than the cell contents, so water leaves the cells by osmosis and the strip loses mass. Sucrose does not readily cross the membrane, and the cell wall does not prevent water movement.

Question 24Module 1

Which comparison of the light-dependent and light-independent reactions of photosynthesis is correct?

  1. Both sets of reactions occur on the thylakoid membranes
  2. The light-independent reactions require light directly to fix carbon dioxide
  3. The light-dependent reactions produce ATP and NADPH used by the light-independent reactions Correct answer.
  4. The light-independent reactions produce ATP used by the light-dependent reactions

Explanation

The light-dependent reactions generate ATP and NADPH, which supply energy and reducing power for carbon fixation in the light-independent reactions. The Calvin cycle occurs in the stroma and does not directly require light.

Question 25Module 1

A respirometer records oxygen uptake by germinating seeds. Which conclusion is best supported if oxygen uptake continues but the respiratory quotient is approximately 1.0?

  1. No respiration is occurring
  2. Anaerobic respiration is the main pathway
  3. The substrate being respired is mainly carbohydrate Correct answer.
  4. The substrate being respired is mainly lipid

Explanation

A respiratory quotient near 1.0 indicates carbohydrate is the main substrate, since carbohydrate oxidation uses oxygen and releases carbon dioxide in roughly equal amounts. Lipids give a quotient below 1.0, and oxygen uptake shows aerobic respiration is occurring.

Question 26Module 1

Which carbohydrate is the principal storage polysaccharide in plant cells and consists of amylose and amylopectin?

  1. Chitin
  2. Cellulose
  3. Starch Correct answer.
  4. Glycogen

Explanation

Starch is the storage polysaccharide of plants, built from alpha-glucose units arranged as helical amylose and branched amylopectin. Glycogen serves the same storage role in animals and fungi, whereas cellulose and chitin are structural polysaccharides.

Question 27Module 1

A triglyceride is formed when glycerol reacts with three fatty acid molecules. Which type of reaction produces this molecule?

  1. Condensation, releasing three water molecules Correct answer.
  2. Oxidation, releasing carbon dioxide
  3. Reduction, consuming hydrogen
  4. Hydrolysis, consuming three water molecules

Explanation

Each fatty acid joins glycerol through an ester bond formed by a condensation reaction, and one water molecule is released per bond, giving three waters in total. Hydrolysis is the reverse process that breaks triglycerides apart.

Question 28Module 1

Which level of protein structure is defined by the linear sequence of amino acids joined by peptide bonds?

  1. Secondary structure
  2. Primary structure Correct answer.
  3. Tertiary structure
  4. Quaternary structure

Explanation

Primary structure is the order of amino acids in the polypeptide chain, held together by covalent peptide bonds. Secondary structure refers to local folding such as alpha-helices, tertiary structure to overall 3D shape, and quaternary structure to assemblies of multiple polypeptides.

Question 29Module 1

A student tests a solution with Benedict's reagent and obtains a brick-red precipitate after heating. Which conclusion is best supported?

  1. A lipid with ester bonds is present
  2. A non-reducing sugar such as sucrose is present
  3. A reducing sugar such as glucose is present Correct answer.
  4. A protein with peptide bonds is present

Explanation

Benedict's reagent is reduced by reducing sugars such as glucose, producing a brick-red precipitate of copper(I) oxide on heating. Sucrose is non-reducing and gives a negative result unless first hydrolysed.

Question 30Module 1

Which statement correctly describes the structure of a phospholipid?

  1. A long hydrocarbon chain with a carboxyl group at one end
  2. A glycerol backbone with three fatty acid chains and no phosphate group
  3. A polymer of amino acids linked by peptide bonds
  4. A glycerol backbone with two fatty acid chains and a phosphate-containing head Correct answer.

Explanation

A phospholipid consists of glycerol bonded to two fatty acid tails and a phosphate-containing head group. The hydrophilic head and hydrophobic tails allow phospholipids to form bilayers in membranes.

Question 31Module 1

Which organelle is the site of aerobic respiration and is bounded by an inner and outer membrane with cristae?

  1. Mitochondrion Correct answer.
  2. Golgi apparatus
  3. Ribosome
  4. Chloroplast

Explanation

The mitochondrion is the site of the later stages of aerobic respiration and has a double membrane, with the inner membrane folded into cristae. Chloroplasts carry out photosynthesis, ribosomes synthesise proteins, and the Golgi modifies and packages molecules.

Question 32Module 1

Which property of the cell membrane is most directly explained by the presence of cholesterol in animal membranes?

  1. Regulation of membrane fluidity across temperature changes Correct answer.
  2. Catalysis of reactions at the membrane surface
  3. Selective transport of sodium ions against a gradient
  4. Recognition of antigens by immune cells

Explanation

Cholesterol sits between phospholipid tails and modifies membrane fluidity, making the membrane less fluid at high temperatures and preventing tight packing at low temperatures. Transport, recognition and catalysis are functions of membrane proteins and glycoproteins.

Question 33Module 1

A cell is placed in a solution with a water potential of −800 kPa, while its cytoplasm has a water potential of −400 kPa. Which movement of water is expected?

  1. Water moves equally in both directions with no net change
  2. Water moves out of the cell by osmosis Correct answer.
  3. Water moves into the cell by osmosis
  4. Water moves into the cell by active transport

Explanation

Water moves by osmosis from a region of higher water potential to a region of lower water potential. The external solution has the lower water potential (−800 kPa), so water moves out of the cell.

Question 34Module 1

Which statement best explains why the rate of an enzyme-controlled reaction falls at temperatures well above the optimum?

  1. The enzyme is used up in the reaction and cannot be replaced
  2. The substrate molecules gain kinetic energy and collide less frequently
  3. The pH of the reaction mixture rises sharply with temperature
  4. The enzyme's active site changes shape as bonds maintaining tertiary structure are broken Correct answer.

Explanation

High temperatures disrupt hydrogen and ionic bonds that maintain the enzyme's tertiary structure, so the active site loses its complementary shape and the enzyme is denatured. Collision frequency actually increases with temperature, so this cannot explain the fall.

Question 35Module 1

A section of one DNA strand reads 5'-TACGGAT-3'. Which sequence is the complementary strand written in the conventional antiparallel orientation?

  1. 3'-ATGCCTA-5' Correct answer.
  2. 5'-AUGCCUA-3'
  3. 3'-TACGGAT-5'
  4. 5'-ATGCCTA-3'

Explanation

Complementary base pairing gives A with T and G with C, and the two strands run antiparallel, so the partner strand reads 3'-ATGCCTA-5'. Writing it as 5'-ATGCCTA-3' would reverse the polarities and give the wrong pairing direction.

Question 36Module 1

During DNA replication, which enzyme joins the Okazaki fragments on the lagging strand?

  1. DNA ligase Correct answer.
  2. RNA polymerase
  3. Primase
  4. DNA helicase

Explanation

DNA ligase catalyses the formation of phosphodiester bonds that seal the nicks between Okazaki fragments. Helicase unwinds the double helix, primase lays down RNA primers, and RNA polymerase transcribes RNA.

Question 37Module 1

Which event occurs during prophase I of meiosis but does not occur during mitosis?

  1. Replication of DNA before division
  2. Condensation of chromosomes
  3. Crossing over between non-sister chromatids of homologous chromosomes Correct answer.
  4. Formation of the spindle apparatus

Explanation

In prophase I, homologous chromosomes pair as bivalents and non-sister chromatids exchange segments by crossing over, creating genetic variation. Spindle formation, chromosome condensation and prior DNA replication also occur in mitosis.

Question 38Module 1

Which process directly explains the independent assortment of alleles for two genes located on different chromosomes?

  1. Random orientation of homologous pairs at the metaphase plate during meiosis I Correct answer.
  2. Crossing over between non-sister chromatids during prophase I
  3. Separation of sister chromatids during anaphase II
  4. Fertilisation of gametes from different parents

Explanation

When homologous pairs align randomly at metaphase I, the maternal and paternal chromosomes of different pairs are distributed independently into gametes. This random orientation underlies independent assortment for genes on separate chromosomes.

Question 39Module 1

Which statement best describes the role of the light-independent reactions of photosynthesis?

  1. They generate a proton gradient across the thylakoid membrane
  2. They absorb light energy using pigments in the thylakoid membrane
  3. They split water to release oxygen and provide electrons
  4. They use ATP and reduced NADP to reduce carbon dioxide and form carbohydrate Correct answer.

Explanation

The light-independent reactions, or Calvin cycle, use ATP and reduced NADP from the light-dependent stage to fix and reduce carbon dioxide into triose phosphate. Water splitting, proton gradients and light absorption all belong to the light-dependent stage.

Question 40Module 1

In an experiment, a respirometer shows that oxygen uptake by germinating seeds is equal to the volume of carbon dioxide released. Which respiratory substrate is most likely being used?

  1. A lipid such as a triglyceride
  2. A protein such as albumin
  3. A carbohydrate such as glucose Correct answer.
  4. A mixture of only amino acids

Explanation

When carbohydrate is fully aerobically respired, the respiratory quotient is about 1.0 because oxygen consumed equals carbon dioxide produced. Lipids and proteins have respiratory quotients below 1.0 because they contain less oxygen relative to carbon and hydrogen.

Question 41Module 1

Which structural feature of the mammalian gas-exchange system most directly increases the rate of diffusion of oxygen into the blood?

  1. Cilia lining the bronchioles
  2. Mucus secreted by goblet cells
  3. Rings of cartilage supporting the trachea
  4. A large surface area with a thin barrier and a steep concentration gradient Correct answer.

Explanation

Fick's law indicates that diffusion rate increases with surface area and concentration gradient and decreases with barrier thickness. Alveoli provide a large, thin surface with a steep gradient maintained by ventilation and blood flow.

Question 42Module 1

Which feature of the mammalian circulatory system is described as a double circulation?

  1. Blood passes through the heart twice in one complete circuit, once via the pulmonary and once via the systemic route Correct answer.
  2. Blood flows twice through the same capillary bed before returning to the heart
  3. Blood is pumped at two different pressures from the same ventricle
  4. Blood flows through two separate hearts, one for each circuit

Explanation

In a double circulation, blood passes through the heart twice per circuit: the right side serves the pulmonary circuit and the left side serves the systemic circuit. This maintains high pressure to the body while keeping lung pressure low.

Question 43Module 1

A plant is placed in a sealed transparent chamber and illuminated with light of a wavelength absorbed poorly by chlorophyll. Which immediate effect is expected on the rate of photosynthesis?

  1. The rate decreases because less light energy is absorbed by photosynthetic pigments Correct answer.
  2. The rate remains unchanged because light intensity is irrelevant
  3. The rate decreases because stomata close in response to light colour
  4. The rate increases because more light is transmitted through the leaf

Explanation

Photosynthesis depends on light energy absorbed by chlorophyll and accessory pigments. Light of poorly absorbed wavelengths provides less excitation energy, so the light-dependent reactions and the overall rate fall.

Question 44Module 1

Which statement correctly distinguishes anabolism from catabolism?

  1. Anabolism occurs only in plants, while catabolism occurs only in animals
  2. Both anabolism and catabolism release energy from complex molecules
  3. Anabolism builds complex molecules using energy, while catabolism breaks molecules down releasing energy Correct answer.
  4. Anabolism breaks molecules down releasing energy, while catabolism builds complex molecules

Explanation

Anabolic reactions such as protein synthesis are endergonic and build larger molecules, whereas catabolic reactions such as respiration are exergonic and break molecules down. Both types occur in all living cells.

Question 45Module 1

A polypeptide has a mutation in which a polar amino acid in the interior of the folded protein is replaced by a non-polar amino acid. Which effect on tertiary structure is most likely?

  1. The primary structure remains unchanged because peptide bonds are unaffected
  2. The protein will necessarily lose all secondary structure
  3. The protein will bind substrates more efficiently regardless of shape
  4. Hydrophobic interactions and hydrogen bonding are altered, changing the overall folding Correct answer.

Explanation

Tertiary structure depends on interactions between R groups, including hydrogen bonds, ionic bonds and hydrophobic interactions. Replacing a polar interior residue with a non-polar one disrupts these interactions and can alter folding and function.

Question 46Module 1

Two enzymes catalyse the same reaction but have different Km values. Enzyme X has a Km of 2 mmol dm⁻³ and enzyme Y has a Km of 10 mmol dm⁻³. Which conclusion is best supported?

  1. Enzyme Y has a greater affinity for the substrate than enzyme X
  2. Enzyme Y has a higher maximum velocity than enzyme X
  3. Enzyme X is denatured at substrate concentrations above 2 mmol dm⁻³
  4. Enzyme X reaches half-maximal velocity at a lower substrate concentration than enzyme Y Correct answer.

Explanation

Km is the substrate concentration at which an enzyme reaches half its maximum velocity, and a lower Km indicates higher affinity. Enzyme X therefore has the greater affinity and reaches half-maximal velocity at a lower substrate concentration.

Question 47Module 1

A cell with a solute potential of −500 kPa and a pressure potential of +100 kPa is placed in a solution of water potential −450 kPa. Which statement correctly predicts the net movement of water?

  1. Water leaves the cell because the cell has the lower water potential
  2. Water enters the cell because the cell has the higher water potential Correct answer.
  3. No net movement occurs because the potentials are equal
  4. Water leaves the cell because pressure potential exceeds solute potential

Explanation

Water potential equals solute potential plus pressure potential, so the cell has a water potential of −400 kPa. Since −400 kPa is higher than the external −450 kPa, water moves into the cell by osmosis.

Question 48Module 1

In a dihybrid cross between two individuals heterozygous for both genes, the observed offspring numbers are 315, 108, 101 and 32 for the four phenotypes. Which conclusion is best supported by these results?

  1. The genes are completely linked and behave as a single gene
  2. The genes show codominance and produce a 1:2:1 ratio
  3. The genes are on different chromosomes and assort independently, fitting a 9:3:3:1 ratio Correct answer.
  4. The genes are sex-linked and show different ratios in males and females

Explanation

The numbers approximate a 9:3:3:1 ratio, which is expected when two genes on different chromosomes assort independently. Linkage would distort the ratio by over-representing parental combinations.

Question 49Module 1

A mutation inserts a single base near the start of a coding sequence. Which consequence is most likely?

  1. A frameshift alters every subsequent codon, usually producing a non-functional protein Correct answer.
  2. The reading frame is restored automatically because the code is degenerate
  3. The mutation has no effect because the code is universal
  4. Only the codon at the insertion site is altered, leaving the rest unchanged

Explanation

Inserting one base shifts the reading frame, so all codons downstream of the mutation are read differently. This usually produces a very different, often truncated, polypeptide that cannot function normally.

Question 50Module 1

An organism has a haploid number of 8. Which number of chromatids is present in a single cell at metaphase II of meiosis?

  1. 4
  2. 16 Correct answer.
  3. 8
  4. 32

Explanation

At metaphase II each cell contains the haploid number of chromosomes, each consisting of two sister chromatids, giving 8 × 2 = 16 chromatids. The diploid number of 16 chromosomes was halved at the end of meiosis I.