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MATSEC IM Biology study materials
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MATSEC IM Biology practice questions

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Question 1Cell biology and biochemistry

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

  1. The rough endoplasmic reticulum
  2. The lysosome
  3. The Golgi apparatus
  4. The mitochondrion Correct answer.

Explanation

The inner mitochondrial membrane carries the electron transport chain and ATP synthase, so oxidative phosphorylation occurs there. The other listed organelles carry out protein processing, secretion and hydrolysis rather than bulk ATP production.

Question 2Cell biology and biochemistry

A student views a specimen with a light microscope using a 10x eyepiece and a 40x objective. What is the total magnification?

  1. 400x Correct answer.
  2. 4000x
  3. 4x
  4. 50x

Explanation

Total magnification is the product of the eyepiece and objective magnifications, so 10 x 40 gives 400x. The other values arise from adding the magnifications or misplacing a factor of ten.

Question 3Cell biology and biochemistry

Which statement correctly describes the behaviour of a red blood cell placed in distilled water?

  1. It swells because solutes move into the cell by diffusion
  2. It shrinks because water leaves the cell by osmosis
  3. It swells and may burst because water enters by osmosis Correct answer.
  4. It remains unchanged because the cell wall resists pressure

Explanation

Distilled water is hypotonic to cytoplasm, so water moves in by osmosis across the partially permeable membrane. Animal cells lack a wall, so the cell swells and can lyse.

Question 4Cell biology and biochemistry

Which bond links two amino acids together in a polypeptide chain?

  1. A phosphodiester bond
  2. A peptide bond Correct answer.
  3. A hydrogen bond
  4. A glycosidic bond

Explanation

A condensation reaction between the carboxyl group of one amino acid and the amino group of the next forms a peptide bond, releasing water. Glycosidic and phosphodiester bonds join sugars and nucleotides respectively.

Question 5Cell biology and biochemistry

Which molecule is the universal hydrogen acceptor at the end of the electron transport chain in aerobic respiration?

  1. Carbon dioxide
  2. Oxygen Correct answer.
  3. NAD+
  4. Pyruvate

Explanation

Oxygen accepts electrons and protons at the end of the chain, forming water and keeping electrons flowing. NAD+ is an electron carrier earlier in the pathway, not the terminal acceptor.

Question 6Cell biology and biochemistry

Which feature distinguishes prokaryotic cells from eukaryotic cells?

  1. Prokaryotic cells have a nucleus enclosed by a double membrane
  2. Prokaryotic cells contain mitochondria but lack chloroplasts
  3. Prokaryotic cells possess 70S ribosomes and no membrane-bound nucleus Correct answer.
  4. Prokaryotic cells lack any genetic material

Explanation

Prokaryotes have 70S ribosomes and a nucleoid of circular DNA without a nuclear envelope. Eukaryotes possess membrane-bound organelles including a true nucleus.

Question 7Cell biology and biochemistry

An enzyme-catalysed reaction is studied as substrate concentration increases while enzyme concentration is fixed. Which change is observed once the substrate is in excess?

  1. The rate plateaus at a maximum value Correct answer.
  2. The enzyme is permanently denatured by excess substrate
  3. The rate falls to zero because substrate inhibits the enzyme
  4. The rate continues to rise in direct proportion to substrate concentration

Explanation

At high substrate concentration all active sites are occupied, so the enzyme is working at its maximum rate and the rate levels off. Adding more substrate cannot increase the rate further until more enzyme is available.

Question 8Cell biology and biochemistry

Which property of water allows insects such as pond skaters to move across a water surface?

  1. Its ability to act as a solvent
  2. Its high surface tension Correct answer.
  3. Its low viscosity
  4. Its high specific heat capacity

Explanation

Hydrogen bonding between water molecules creates strong cohesion at the air-water interface, producing high surface tension that supports small bodies. Specific heat and solvent behaviour do not explain surface support.

Question 9Cell biology and biochemistry

A cell is treated with a drug that blocks the S phase of the cell cycle. Which process is directly prevented?

  1. Formation of the mitotic spindle
  2. Separation of sister chromatids
  3. Cytokinesis of the daughter cells
  4. Replication of chromosomal DNA Correct answer.

Explanation

DNA replication occurs during S phase, so blocking this phase prevents chromosomes from being duplicated. Chromatid separation, spindle formation and cytokinesis occur later in M phase.

Question 10Cell biology and biochemistry

Which statement best explains why a competitive inhibitor reduces the rate of an enzyme-controlled reaction?

  1. It lowers the activation energy of the reaction
  2. It permanently denatures the tertiary structure of the enzyme
  3. It binds to an allosteric site and changes the shape of the active site
  4. It binds to the active site and blocks substrate access Correct answer.

Explanation

A competitive inhibitor resembles the substrate and occupies the active site, so fewer enzyme molecules are available to bind substrate. Its effect can be reduced by raising substrate concentration.

Question 11Cell biology and biochemistry

Which of these correctly pairs a polysaccharide with its storage role?

  1. Chitin is a soluble sugar used in glycolysis
  2. Starch is a structural component of fungal cell walls
  3. Cellulose is the main energy store in plant seeds
  4. Glycogen is a branched storage carbohydrate in animals Correct answer.

Explanation

Glycogen is a highly branched glucose polymer stored in liver and muscle cells, allowing rapid mobilisation. Cellulose and chitin are structural, while starch is the plant storage polysaccharide.

Question 12Cell biology and biochemistry

During which stage of aerobic respiration is the majority of carbon dioxide released?

  1. Glycolysis in the cytoplasm
  2. The Krebs cycle in the mitochondrial matrix Correct answer.
  3. The electron transport chain on the inner membrane
  4. Lactate formation during anaerobic respiration

Explanation

Decarboxylation reactions in the Krebs cycle release two molecules of carbon dioxide per acetyl group, accounting for most of the carbon dioxide produced. Glycolysis and the electron transport chain do not release carbon dioxide.

Question 13Cell biology and biochemistry

Which structural feature of the phospholipid bilayer allows small non-polar molecules to cross the membrane readily?

  1. The presence of peripheral proteins on the outer surface
  2. The hydrophobic fatty acid tails forming the interior Correct answer.
  3. The hydrophilic phosphate heads facing the aqueous exterior
  4. The cholesterol molecules embedded between phospholipids

Explanation

The hydrophobic core formed by fatty acid tails repels polar substances but allows lipid-soluble, non-polar molecules to dissolve and diffuse through. This is why gases and steroids cross membranes easily.

Question 14Cell biology and biochemistry

A sample of DNA contains 20% adenine. What percentage of its bases is guanine?

  1. 20%
  2. 30% Correct answer.
  3. 60%
  4. 40%

Explanation

By complementary base pairing, adenine equals thymine, so A + T = 40% and G + C = 60%. Since guanine equals cytosine, guanine is 30%.

Question 15Cell biology and biochemistry

Which description correctly matches a stage of mitosis?

  1. Anaphase: the nuclear envelope reforms around each chromosome set
  2. Metaphase: chromosomes line up along the spindle equator Correct answer.
  3. Telophase: sister chromatids are pulled to opposite poles
  4. Prophase: chromosomes align on the equator of the cell

Explanation

During metaphase, chromosomes become attached to spindle fibres and align along the metaphase plate at the cell equator. Alignment is the defining event of this stage.

Question 16Cell biology and biochemistry

Which statement about the fluid mosaic model of the plasma membrane is correct?

  1. Carbohydrate chains are attached only to the inner face of the membrane
  2. The membrane consists of a single layer of phospholipids
  3. Proteins are fixed in position within a rigid phospholipid layer
  4. Phospholipids and many proteins can move laterally within the membrane Correct answer.

Explanation

The model describes a dynamic bilayer in which phospholipids and many proteins diffuse laterally, giving the membrane fluidity. Glycoproteins and glycolipids face the extracellular environment.

Question 17Cell biology and biochemistry

Why is the reaction catalysed by an enzyme described as lowering the activation energy?

  1. It increases the kinetic energy of the substrate molecules
  2. It makes the reaction exothermic overall
  3. It increases the concentration of the substrate
  4. It provides an alternative reaction pathway requiring less energy Correct answer.

Explanation

Enzymes stabilise the transition state and provide a lower-energy route from substrate to product, so more molecules can react at a given temperature. They do not change the overall energy change of the reaction.

Question 18Cell biology and biochemistry

A plant cell with a solute potential of -800 kPa and a pressure potential of +300 kPa is placed in pure water. What is its water potential?

  1. -1100 kPa
  2. -500 kPa Correct answer.
  3. -300 kPa
  4. +500 kPa

Explanation

Water potential equals solute potential plus pressure potential, so -800 + 300 gives -500 kPa. Pure water has a water potential of zero, so water will tend to enter the cell.

Question 19Cell biology and biochemistry

Which feature of the enzyme active site best explains the specificity of enzyme action?

  1. The active site contains only amino acids with hydrophobic side chains
  2. The active site shape is complementary to a specific substrate Correct answer.
  3. The active site is always negatively charged
  4. The active site is formed by the substrate itself

Explanation

Specificity arises because the active site has a shape and chemistry complementary to a particular substrate, forming a temporary enzyme-substrate complex. Only substrates that fit can be catalysed.

Question 20Cell biology and biochemistry

Which statement correctly describes the role of the Golgi apparatus in a secretory cell?

  1. It produces ribosomes for protein synthesis
  2. It modifies proteins received from the rough endoplasmic reticulum and packages them into vesicles Correct answer.
  3. It synthesises ATP for vesicle transport
  4. It replicates DNA before cell division

Explanation

The Golgi apparatus receives proteins from the rough endoplasmic reticulum, modifies them, and packages them into vesicles for secretion or delivery. This is central to the secretory pathway.

Question 21Cell biology and biochemistry

A culture of cells is grown in a medium containing radioactive thymine. Which cellular process will incorporate the label into the nucleus?

  1. Translation of proteins on ribosomes
  2. Transcription of messenger RNA
  3. DNA replication during S phase Correct answer.
  4. Formation of the spindle during mitosis

Explanation

Thymine is a base found in DNA, so radioactive thymine is incorporated wherever DNA is synthesised, namely during replication in S phase. RNA lacks thymine and protein synthesis does not use it.

Question 22Cell biology and biochemistry

Two enzyme samples act on the same substrate, but enzyme X has a much lower Michaelis constant than enzyme Y. What can be concluded?

  1. Enzyme Y is denatured at all substrate concentrations
  2. Enzyme Y reaches maximum velocity at lower substrate concentration
  3. Enzyme X has a higher maximum velocity than enzyme Y
  4. Enzyme X has a greater affinity for the substrate than enzyme Y Correct answer.

Explanation

A low Michaelis constant indicates that half-maximal velocity is reached at a low substrate concentration, reflecting high affinity between enzyme and substrate. It does not by itself indicate the maximum velocity.

Question 23Cell biology and biochemistry

In an experiment, an enzyme is incubated at 70 degrees Celsius and then cooled to its optimum temperature. The reaction rate remains very low. What is the best explanation?

  1. The substrate was used up during heating
  2. The active sites became saturated with product
  3. The high temperature permanently changed the tertiary structure of the enzyme Correct answer.
  4. The enzyme requires a cofactor that was destroyed by cooling

Explanation

Excessive heat breaks the hydrogen and ionic bonds maintaining tertiary structure, irreversibly denaturing the enzyme so that active sites lose their shape. Cooling cannot restore the original conformation.

Question 24Cell biology and biochemistry

A length of DNA has the template strand sequence 3'-TAC GGA TTC-5'. Which mRNA sequence is produced by transcription?

  1. 5'-TAC GGA TTC-3'
  2. 5'-ATG CCT AAG-3'
  3. 5'-UAC GGA UUC-3'
  4. 5'-AUG CCU AAG-3' Correct answer.

Explanation

Transcription builds mRNA complementary and antiparallel to the template strand, with uracil replacing thymine. A pairs with U, T pairs with A, G with C and C with G, giving 5'-AUG CCU AAG-3'.

Question 25Cell biology and biochemistry

An organism's cells have a solute potential of -600 kPa and are bathed in a solution of water potential -400 kPa. What is the expected net movement of water and why?

  1. Water leaves the cells because the external solution has a lower water potential
  2. Water enters the cells because the solute potential is more negative
  3. There is no net movement because the potentials are equal
  4. Water enters the cells because the external solution has a higher water potential Correct answer.

Explanation

Water moves from higher to lower water potential, and -400 kPa is higher than -600 kPa, so water enters the cells. The more negative solute potential of the cells drives the inward flow.

Question 26Cell biology and biochemistry

A student views a cell and observes a rigid cellulose wall, a large permanent vacuole and chloroplasts. Which type of cell is being observed?

  1. A bacterial cell
  2. A fungal cell
  3. A plant cell Correct answer.
  4. An animal cell

Explanation

Cellulose walls, a large permanent vacuole and chloroplasts are together characteristic of plant cells. Fungal walls are chitin, bacterial walls are peptidoglycan, and animal cells lack walls and chloroplasts.

Question 27Cell biology and biochemistry

Which bond links two adjacent amino acids in a polypeptide chain?

  1. A peptide bond Correct answer.
  2. A hydrogen bond
  3. A phosphodiester bond
  4. A glycosidic bond

Explanation

A condensation reaction between the carboxyl group of one amino acid and the amino group of the next forms a peptide bond. Glycosidic bonds join sugars, phosphodiester bonds join nucleotides, and hydrogen bonds are weaker interactions rather than the covalent backbone link.

Question 28Cell biology and biochemistry

Which reagent is used to test a food sample for the presence of reducing sugar, and what positive result is seen?

  1. Iodine solution, giving a blue-black colour
  2. Biuret reagent, giving a purple colour
  3. Benedict's solution, giving a brick-red precipitate on heating Correct answer.
  4. Emulsion test with ethanol, giving a cloudy white layer

Explanation

Benedict's reagent contains copper(II) ions that are reduced to copper(I) oxide by reducing sugars on heating, producing a brick-red precipitate. Iodine tests for starch, Biuret for protein and the emulsion test for lipid.

Question 29Cell biology and biochemistry

Which statement describes the behaviour of a semi-conservative mechanism of DNA replication?

  1. The original double helix remains intact and a completely new helix is made
  2. Both strands of a new DNA molecule are newly synthesised
  3. Only one strand of the original helix is copied, producing a single-stranded molecule
  4. Each new DNA molecule contains one original strand and one newly synthesised strand Correct answer.

Explanation

In semi-conservative replication the two strands separate and each acts as a template, so every daughter helix has one conserved parental strand and one new strand. This was demonstrated by the Meselson-Stahl experiment.

Question 30Cell biology and biochemistry

Which molecule is the immediate energy donor for the contraction of a muscle fibre?

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

Explanation

Hydrolysis of ATP to ADP and inorganic phosphate releases the energy used directly by the myosin cross-bridge cycle. Glucose, NADH and pyruvate are substrates or carriers that must first be oxidised to regenerate ATP.

Question 31Cell biology and biochemistry

Which structural feature of the cell surface membrane makes it described as partially permeable?

  1. A fully hydrophobic membrane with no embedded proteins
  2. A hydrophobic phospholipid bilayer that restricts polar and charged substances Correct answer.
  3. A rigid layer of cellulose fibres surrounding the membrane
  4. A continuous layer of protein covering the whole surface

Explanation

The hydrophobic fatty acid tails in the interior restrict the passage of polar and charged molecules, while small non-polar substances dissolve through readily. This selective restriction is what makes the membrane partially permeable.

Question 32Cell biology and biochemistry

Which process moves oxygen from the alveoli into the blood without the use of ATP?

  1. Active transport using carrier proteins
  2. Endocytosis into capillary cells
  3. Osmosis through aquaporins
  4. Simple diffusion down a concentration gradient Correct answer.

Explanation

Oxygen is small and non-polar, so it diffuses directly through the alveolar and capillary membranes down its concentration gradient. This passive movement requires no ATP, unlike active transport or endocytosis.

Question 33Cell biology and biochemistry

A cell is placed in a solution whose water potential is higher than that of its cytoplasm. What is the immediate effect on the cell?

  1. Solute moves out of the cell by active transport
  2. There is no net movement of water
  3. Water leaves the cell by osmosis
  4. Water enters the cell by osmosis Correct answer.

Explanation

Water moves by osmosis from the region of higher water potential to the region of lower water potential. Since the external solution has the higher water potential, water enters the cell.

Question 34Cell biology and biochemistry

Which feature of the genetic code explains why a substitution mutation in the third base of a codon often has no effect on the polypeptide?

  1. The code is universal across almost all organisms
  2. The code contains start and stop signals
  3. The code is degenerate, so several codons specify the same amino acid Correct answer.
  4. The code is non-overlapping

Explanation

Degeneracy means more than one codon can code for the same amino acid, so a change in the third base may still give the same residue. Universality, non-overlapping reading and stop signals do not by themselves protect against a change in meaning.

Question 35Cell biology and biochemistry

In an enzyme-controlled reaction, doubling the substrate concentration produces no further increase in rate. Which explanation is correct?

  1. The activation energy of the reaction has increased
  2. The substrate has become a competitive inhibitor
  3. All active sites are occupied, so the enzyme is saturated Correct answer.
  4. The enzyme has been denatured by the substrate

Explanation

At saturation every active site is occupied at any instant, so adding more substrate cannot increase the number of reactions per unit time. The rate then depends on enzyme concentration, not substrate concentration.

Question 36Cell biology and biochemistry

Which statement explains why a non-competitive inhibitor cannot be overcome by increasing substrate concentration?

  1. It binds to a site other than the active site and changes the shape of the active site Correct answer.
  2. It binds reversibly to the active site and competes with the substrate
  3. It permanently denatures the enzyme by breaking peptide bonds
  4. It lowers the substrate concentration by reacting with it

Explanation

A non-competitive inhibitor binds at an allosteric site, altering the tertiary structure of the active site so the substrate fits less well. Because the inhibitor does not compete for the active site, adding more substrate does not displace it.

Question 37Cell biology and biochemistry

A length of DNA has the coding strand sequence 5'-ATG CCT GAA-3'. Which mRNA sequence is transcribed from the template strand?

  1. 5'-UAC GGA CUU-3'
  2. 5'-TAC GGA CTT-3'
  3. 5'-AUG CCU GAA-3' written in the reverse direction
  4. 5'-AUG CCU GAA-3' Correct answer.

Explanation

The mRNA is identical in sequence to the coding strand except that uracil replaces thymine, so it reads 5'-AUG CCU GAA-3'. The template strand would be complementary and antiparallel, giving UAC GGA CUU, but that is not the mRNA product.

Question 38Cell biology and biochemistry

During which phase of the cell cycle does DNA replication occur?

  1. Cytokinesis
  2. Prophase of mitosis
  3. S phase of interphase Correct answer.
  4. G1 phase of interphase

Explanation

DNA is replicated during the S (synthesis) phase of interphase, so each chromosome becomes two sister chromatids. G1 is growth before replication, prophase is when chromosomes condense, and cytokinesis divides the cytoplasm.

Question 39Cell biology and biochemistry

A plant cell has a solute potential of -700 kPa and a pressure potential of +200 kPa. What is its water potential?

  1. +500 kPa
  2. -900 kPa
  3. -700 kPa
  4. -500 kPa Correct answer.

Explanation

Water potential is the sum of solute potential and pressure potential: -700 + 200 = -500 kPa. Pressure potential is positive in a turgid plant cell and therefore raises (makes less negative) the water potential.

Question 40Cell biology and biochemistry

Which process produces the greatest yield of ATP per molecule of glucose in aerobic respiration?

  1. Oxidative phosphorylation on the inner mitochondrial membrane Correct answer.
  2. The link reaction in the mitochondrial matrix
  3. The Krebs cycle in the mitochondrial matrix
  4. Glycolysis in the cytoplasm

Explanation

Most ATP is generated by oxidative phosphorylation, where the electron transport chain establishes a proton gradient used by ATP synthase. Glycolysis, the link reaction and the Krebs cycle yield only small net amounts of ATP directly, though they supply reduced coenzymes.

Question 41Cell biology and biochemistry

Which statement describes the role of chlorophyll in the light-dependent reaction of photosynthesis?

  1. It splits glucose to release carbon dioxide
  2. It reduces NADP using ATP produced in the Calvin cycle
  3. It absorbs light energy and excites electrons that are passed along an electron transport chain Correct answer.
  4. It fixes carbon dioxide into an organic molecule

Explanation

Chlorophyll absorbs photons, exciting electrons that are transferred through carriers, generating ATP and reduced NADP and driving photolysis of water. Carbon fixation occurs later in the light-independent reaction.

Question 42Cell biology and biochemistry

A section of DNA contains 30% of its bases as cytosine. What percentage of its bases is thymine?

  1. 20% Correct answer.
  2. 40%
  3. 30%
  4. 70%

Explanation

By complementary base pairing the percentage of guanine equals that of cytosine, so G + C = 60%. The remaining 40% is shared equally between adenine and thymine, giving 20% thymine.

Question 43Cell biology and biochemistry

Which feature of the active site of an enzyme explains why it is specific for one substrate?

  1. It is formed entirely of hydrogen bonds that are not specific
  2. Its shape is complementary to the substrate so only that substrate fits Correct answer.
  3. It contains a phosphate group that binds any nucleotide
  4. It has a random shape that fits any molecule of the correct size

Explanation

The active site has a specific three-dimensional shape and chemical character complementary to its substrate, so only molecules that fit closely can bind and react. This complementarity is the basis of enzyme specificity.

Question 44Cell biology and biochemistry

A student counts 40 cells in a root tip and finds 10 of them in anaphase. Which conclusion is valid?

  1. The sample contains only cells that are dividing
  2. The cells in anaphase have just completed cytokinesis
  3. Anaphase occupies about one quarter of the time of the whole cell cycle in this sample Correct answer.
  4. Anaphase is the longest phase of mitosis

Explanation

The proportion of cells in a stage reflects the relative duration of that stage, so 10 out of 40 cells suggests anaphase lasts about 25% of the cycle. It does not mean anaphase is the longest phase unless its proportion is the largest.

Question 45Cell biology and biochemistry

An enzyme has an optimum temperature of 37 degrees Celsius. When it is heated to 80 degrees Celsius and then cooled to 37 degrees Celsius, the reaction rate remains very low. Which explanation is correct?

  1. The substrate has been used up during heating
  2. The tertiary structure of the active site has been permanently altered Correct answer.
  3. The enzyme is temporarily inhibited and will recover over time
  4. The enzyme has been diluted by the heating

Explanation

High temperature breaks the hydrogen and ionic bonds maintaining the tertiary structure, irreversibly denaturing the active site. Cooling cannot restore the original shape, so the rate stays low.

Question 46Cell biology and biochemistry

In an experiment, a length of DNA is transcribed in a medium containing radioactive uracil and then translated. Where would the radioactivity be detected in the polypeptide-producing machinery?

  1. In the polypeptide chain only
  2. In the ribosomal proteins only
  3. In the tRNA molecules only
  4. In the mRNA bound to ribosomes Correct answer.

Explanation

Radioactive uracil is incorporated into the newly synthesised mRNA during transcription, so the label appears in mRNA. The polypeptide contains no uracil, and any label in tRNA or ribosomes would come from other sources.

Question 47Cell biology and biochemistry

A mutation changes a single base in the promoter region of a gene. Which is the most likely consequence?

  1. The rate of transcription of the gene may change Correct answer.
  2. DNA replication will be completely prevented
  3. The gene will be moved to a different chromosome
  4. The amino acid sequence of the protein will necessarily change

Explanation

The promoter is where RNA polymerase and transcription factors bind, so a change there can alter how efficiently the gene is transcribed. Because the promoter is not translated, the amino acid sequence is not directly changed.

Question 48Cell biology and biochemistry

Which observation supports the claim that the cell surface membrane is fluid rather than rigid?

  1. Membrane proteins and phospholipids can move laterally within the bilayer Correct answer.
  2. The membrane contains cholesterol molecules
  3. The membrane has carbohydrates attached to proteins
  4. The membrane is about 7 nm thick

Explanation

Lateral movement of phospholipids and proteins, demonstrated by techniques such as fluorescence recovery, shows the membrane behaves as a fluid mosaic. Presence of cholesterol, thickness and glycoproteins do not by themselves demonstrate fluidity.

Question 49Cell biology and biochemistry

A dialysis tubing bag containing a starch and glucose solution is placed in distilled water. After one hour, which result is expected?

  1. Glucose is detected in the surrounding water but starch is not Correct answer.
  2. Neither glucose nor starch is detected in the surrounding water
  3. Starch is detected in the surrounding water but glucose is not
  4. Both glucose and starch are detected in the surrounding water

Explanation

Dialysis tubing is partially permeable, so small glucose molecules diffuse out while large starch molecules cannot pass through the pores. The surrounding water therefore tests positive for glucose but not for starch.

Question 50Cell biology and biochemistry

A polypeptide is synthesised on a ribosome and then secreted from a pancreatic cell. Which sequence correctly describes the route taken by the polypeptide through the endomembrane system?

  1. Rough endoplasmic reticulum, lysosome, Golgi apparatus, transport vesicle, cell surface membrane
  2. Smooth endoplasmic reticulum, Golgi apparatus, lysosome, secretory vesicle, cell surface membrane
  3. Rough endoplasmic reticulum, transport vesicle, Golgi apparatus, secretory vesicle, cell surface membrane Correct answer.
  4. Golgi apparatus, rough endoplasmic reticulum, transport vesicle, secretory vesicle, cell surface membrane

Explanation

Polypeptides destined for secretion are synthesised on ribosomes bound to the rough endoplasmic reticulum and pass into its lumen, where folding begins. They leave in transport vesicles that fuse with the cis face of the Golgi apparatus, where modification and packaging occur, and are then carried in secretory vesicles to the cell surface membrane for exocytosis. The order of the compartments is fixed, so any route that reverses or omits a stage is incorrect.