Practice gce model questions vol1 biology 2021 Past Questions

Question 1 View Details

An adult weighing \(65 \text{ kg}\) has measured urinary nitrogen loss of \(11 \text{ g}\) per day and estimated non‑urinary nitrogen losses of \(2 \text{ g}\) per day. Assuming that protein is \(16\%\) nitrogen by weight, what is the minimum amount of protein (in grams, to the nearest gram) the adult must consume each day to achieve zero nitrogen balance?

A. 84 g

Correct B. 81 g

C. 90 g

D. 78 g

Correct Answer: B

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Question 2 View Details

During a renal clearance test, a substance X has a plasma concentration of \(0.8 \text{ mg·mL}^{-1}\) and a urine concentration of \(2.4 \text{ mg·mL}^{-1}\). The urine flow rate is \(1.5 \text{ mL·min}^{-1}\). (a) Calculate the clearance of X in \(\text{mL·min}^{-1}\). (b) If the glomerular filtration rate (GFR) is \(125 \text{ mL·min}^{-1}\), state whether X is predominantly filtered, reabsorbed, or secreted.

Correct A. a) 4.5 mL·min⁻¹; b) predominantly reabsorbed

B. a) 4.5 mL·min⁻¹; b) predominantly secreted

C. a) 6.0 mL·min⁻¹; b) predominantly secreted

D. a) 3.0 mL·min⁻¹; b) predominantly filtered

Correct Answer: A

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Question 3 View Details

In a 10‑year cohort study of 2000 individuals, 800 were smokers and 1200 were non‑smokers. By the end of the study, 120 smokers and 30 non‑smokers had developed lung cancer. (a) Calculate the relative risk (RR) of lung cancer for smokers compared with non‑smokers. (b) Determine the attributable risk percent among the exposed (smokers). (c) Compute the population attributable risk percent for the whole cohort.

A. RR = 7.0; AR% ≈ 85.7%; PAR% ≈ 70.0%

B. RR = 5.0; AR% ≈ 80.0%; PAR% ≈ 60.0%

C. RR = 4.0; AR% ≈ 75.0%; PAR% ≈ 55.0%

Correct D. RR = 6.0; AR% ≈ 83.3%; PAR% ≈ 66.7%

Correct Answer: D

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Question 4 View Details

A mountaineer ascends to an altitude of \(3500 \text{ m}\). At sea level his arterial \(\text{PO}_2\) is \(95 \text{ mmHg}\), haemoglobin concentration \(13 \text{ g·dL}^{-1}\) and arterial oxygen saturation \(S_{a}\text{O}_2 = 0.97\). At altitude his arterial \(\text{PO}_2\) falls to \(55 \text{ mmHg}\) and \(S_{a}\text{O}_2\) drops to \(0.85\), but his haemoglobin concentration rises to \(15 \text{ g·dL}^{-1}\). Using the equation \(C_{a}\text{O}_2 = (1.34 \times \text{Hb} \times S_{a}\text{O}_2) + (0.0031 \times \text{PO}_2)\), calculate (i) the arterial oxygen content at sea level and at altitude (in \(\text{mL·dL}^{-1}\)), and (ii) the percentage change in \(C_{a}\text{O}_2\) from sea level to altitude.

A. (i) Sea level ≈ 18.0 mL·dL⁻¹; altitude ≈ 17.2 mL·dL⁻¹. (ii) ≈ ‑4.4 % decrease

B. (i) Sea level ≈ 16.8 mL·dL⁻¹; altitude ≈ 16.9 mL·dL⁻¹. (ii) ≈ 0.6 % increase

C. (i) Sea level ≈ 17.5 mL·dL⁻¹; altitude ≈ 17.0 mL·dL⁻¹. (ii) ≈ ‑2.9 % decrease

Correct D. (i) Sea level ≈ 17.2 mL·dL⁻¹; altitude ≈ 17.3 mL·dL⁻¹. (ii) ≈ 0.3 % increase

Correct Answer: D

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Question 5 View Details

In a large population a recessive genetic disorder occurs in 1 in 2500 individuals. The disease allele also confers a heterozygote advantage: heterozygotes have a fitness 10 % higher than normal homozygotes, while homozygous recessives have a fitness 50 % lower than normal homozygotes. Assuming Hardy-Weinberg equilibrium and random mating: (a) Calculate the allele frequency (\(q\)) of the disease allele. (b) Determine the expected proportion of heterozygotes in the next generation after selection (as a percentage, to one decimal place).

A. q = 0.01; heterozygote proportion ≈ 2.0%

Correct B. q = 0.02; heterozygote proportion ≈ 4.3%

C. q = 0.025; heterozygote proportion ≈ 5.1%

D. q = 0.04; heterozygote proportion ≈ 7.6%

Correct Answer: B

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Question 6 View Details

During exposure to a hot environment (ambient temperature \(30^{\circ}\text{C}\)), a person with a core temperature of \(37^{\circ}\text{C}\) generates metabolic heat at a rate of \(100\ \text{W}\). Heat is lost by convection, modelled as \(Q_{\text{conv}} = hA(T_{\text{body}}-T_{\text{env}})\) with \(hA = 10\ \text{W}\,^{\circ}\text{C}^{-1}\), and by evaporation of sweat at a rate of \(0.5\ \text{g min}^{-1}\). The latent heat of vapourisation of water is \(2.43\ \text{MJ kg}^{-1}\). Will the person's core temperature increase, decrease, or remain constant? State the expected direction.

A. stay the same

B. remain constant

C. decrease

Correct D. increase

Correct Answer: D

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Question 7 View Details

Food A contains 20 % protein, its protein is 90 % digestible and lysine makes up 5 % of its protein. Food B contains 15 % protein, its protein is 80 % digestible and lysine makes up 8 % of its protein. An adult needs at least 30 g of total protein and 2.5 g of digestible lysine per day. What is the minimum total mass of food (in grams, to the nearest gram) that must be eaten to satisfy both requirements? Assume the foods can be mixed in any proportion.

A. 275

Correct B. 260

C. 300

D. 250

Correct Answer: B

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Question 8 View Details

A simple stretch reflex involves a sensory neuron of length \(0.5\ \text{m}\) conducting at \(80\ \text{m s}^{-1}\), a motor neuron of length \(0.4\ \text{m}\) conducting at \(60\ \text{m s}^{-1}\), and a single synaptic delay of \(0.5\ \text{ms}\). Calculate the total time (in milliseconds) from the onset of muscle stretch to the resulting muscle contraction. Is this time less than the \(30\ \text{ms}\) required for effective postural stability? Give the total time and answer Yes or No.

A. 12.8 ms, No

B. 15.2 ms, Yes

C. 28.0 ms, Yes

Correct D. 13.4 ms, Yes

Correct Answer: D

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Question 9 View Details

In the follicular phase of the menstrual cycle, estrogen concentration rises by \(30\ \text{pg mL}^{-1}\) each day but 10 % of the existing estrogen is cleared each day. Starting from a concentration of 0 pg mL\(^{-1}\) on day 8, on which day does the concentration first reach or exceed the LH‑surge threshold of \(200\ \text{pg mL}^{-1}\)? Give the day number of the cycle.

A. 20

Correct B. 19

C. 22

D. 18

Correct Answer: B

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Question 10 View Details

In a diploid population with effective size \(N_e = 10{,}000\), a new advantageous allele arises with selection coefficient \(s = 0.01\) (heterozygote fitness \(1+s\)). Using the approximation \(P_{\text{fix}} \approx 2s\) for a beneficial allele, estimate the probability that this allele will become fixed. Compare this to the neutral fixation probability \(1/(2N_e)\) and state how many times larger the advantageous probability is.

A. 0.02; 200 times larger

Correct B. 0.02; 400 times larger

C. 0.01; 200 times larger

D. 0.04; 800 times larger

Correct Answer: B

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Question 11 View Details

A disease has a basic reproduction number \(R_0 = 3.5\). A vaccine is \(80\%\) effective at preventing infection. (a) What proportion of the total population must be vaccinated to achieve herd immunity? (b) If only \(60\%\) of the population can be vaccinated, what is the effective reproduction number after vaccination? Give your answers as decimals rounded to two significant figures.

A. Vaccination coverage ≈ 0.89; effective \(R \approx 2.1\)

B. Vaccination coverage ≈ 0.95; effective \(R \approx 1.5\)

C. Vaccination coverage ≈ 0.71; effective \(R \approx 1.8\)

Correct D. Vaccination coverage ≈ 0.89; effective \(R \approx 1.8\)

Correct Answer: D

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Question 12 View Details

In a bacterial culture, the cell density rises from \(2.0 \times 10^{6}\) CFU ml\(^{-1}\) at time 0 to \(1.6 \times 10^{8}\) CFU ml\(^{-1}\) after 4 h, assuming exponential growth. (a) Determine the generation time in minutes (to the nearest minute). (b) An antibiotic is added that reduces the growth‑rate constant by 30 % for the next 6 h. What will be the bacterial density after those 6 h? Express your answer in scientific notation with two significant figures.

A. Generation time = 30 min; final density ≈ 3.4×10^{9} CFU ml^{-1}

B. Generation time = 50 min; final density ≈ 2.0×10^{10} CFU ml^{-1}

Correct C. Generation time = 38 min; final density ≈ 1.6×10^{10} CFU ml^{-1}

D. Generation time = 45 min; final density ≈ 1.1×10^{11} CFU ml^{-1}

Correct Answer: C

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Question 13 View Details

A plant cell membrane has a permeability coefficient for glucose of \(P = 2.5 \times 10^{-5}\,\text{cm\,s}^{-1}\) and a surface area of \(A = 1.2 \times 10^{-4}\,\text{cm}^{2}\). The external glucose concentration is \(5\ \text{mM}\) and the internal concentration is \(0.5\ \text{mM}\). (a) Calculate the rate of passive diffusion of glucose into the cell in µmol s\(^{-1}\). (b) The cell also possesses a glucose transporter that follows Michaelis-Menten kinetics with \(V_{\max}=2.0 \times 10^{-7}\,\text{mol\,s}^{-1}\) and \(K_{m}=2\ \text{mM}\). Determine the total glucose uptake rate (passive + active) under the same concentrations, giving your answer in µmol s\(^{-1}\) to two decimal places.

A. Total uptake ≈ 0.22 µmol s⁻¹

B. Total uptake ≈ 0.05 µmol s⁻¹

C. Total uptake ≈ 0.09 µmol s⁻¹

Correct D. Total uptake ≈ 0.14 µmol s⁻¹

Correct Answer: D

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Question 14 View Details

Which organelle is the primary site of ATP production through oxidative phosphorylation in eukaryotic cells?

A. ribosome

Correct B. mitochondrion

C. nucleus

D. chloroplast

Correct Answer: B

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Question 15 View Details

A subject receives an inulin infusion that yields a steady plasma inulin concentration of \(0.12\ \text{mg ml}^{-1}\). Over a 2‑minute collection, \(48\ \text{mg}\) of inulin are recovered in \(120\ \text{ml}\) of urine. (a) Calculate the glomerular filtration rate (GFR) in ml min\(^{-1}\). (b) The plasma creatinine concentration is \(0.009\ \text{mg ml}^{-1}\) and the urine creatinine concentration is \(0.036\ \text{mg ml}^{-1}\). Estimate the creatinine clearance and state whether it over‑ or under‑estimates the GFR. Give both clearances to one decimal place.

Correct A. GFR = 200.0 ml min⁻¹; creatinine clearance = 240.0 ml min⁻¹ (overestimates GFR)

B. GFR = 200.0 ml min⁻¹; creatinine clearance = 240.0 ml min⁻¹ (underestimates GFR)

C. GFR = 180.0 ml min⁻¹; creatinine clearance = 240.0 ml min⁻¹ (overestimates GFR)

D. GFR = 200.0 ml min⁻¹; creatinine clearance = 210.0 ml min⁻¹ (underestimates GFR)

Correct Answer: A

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Question 16 View Details

The diagram shows the stages of mitosis labelled A, B, C and D. Stage B corresponds to the stage where chromosomes line up at the cell's equatorial plate. Identify the name of this stage.

A. Telophase

B. Prophase

C. Anaphase

Correct D. Metaphase

Correct Answer: D

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Question 17 View Details

A newly discovered multicellular eukaryote has cell walls made of cellulose, contains chloroplasts, lacks true vascular tissue, reproduces via spores and shows alternation of generations. Based on these characteristics, what is the most specific taxonomic rank (kingdom, phylum, class, order, family, genus or species) that can be confidently assigned to this organism?

A. Class Marchantiopsida

B. Class Anthocerotopsida

Correct C. Class Bryopsida

D. Class Sphagnopsida

Correct Answer: C

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Question 18 View Details

In a dihybrid cross, two genes A/a and B/b are linked on the same chromosome with a recombination frequency of 10 %. The heterozygous parent has the coupling arrangement AB/ab and is crossed with a homozygous recessive parent ab/ab. What is the probability (as a percentage) that an offspring will be homozygous recessive (ab/ab) for both genes?

A. 40%

B. 50%

C. 55%

Correct D. 45%

Correct Answer: D

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Question 19 View Details

The labelled diagram of an animal cell shows organelles A, B, C and D. Organelle B is the mitochondrion. Which organelle is primarily responsible for the production of ATP in the cell?

A. Nucleus

B. Chloroplast

C. Ribosome

Correct D. Mitochondrion

Correct Answer: D

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Question 20 View Details

Ecosystem A has a primary‑producer biomass of 5000 g m⁻², a herbivore biomass of 500 g m⁻² and a carnivore biomass of 50 g m⁻². Ecosystem B has a primary‑producer biomass of 8000 g m⁻², a herbivore biomass of 400 g m⁻² and a carnivore biomass of 80 g m⁻². Assuming that the energy transfer efficiency between successive trophic levels is given by the ratio of the consumer biomass to the resource biomass, calculate the average trophic‑transfer efficiency for each ecosystem (average of the producer→herbivore and herbivore→carnivore efficiencies) and state which ecosystem has the higher overall average efficiency.

A. Both ecosystems have equal average efficiency

B. Neither ecosystem; efficiencies cannot be compared

Correct C. Ecosystem B

D. Ecosystem A

Correct Answer: C

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Question 21 View Details

At an altitude where the barometric pressure is 405 mmHg, the fraction of inspired oxygen is 0.21, water vapour pressure in the alveoli is 47 mmHg, and arterial \(P_{CO_2}\) is 40 mmHg. Assuming a respiratory quotient of 0.8, calculate the alveolar partial pressure of oxygen (\(P_{A}O_2\)). Give your answer to the nearest whole mmHg.

A. 20

B. 30

C. 35

Correct D. 25

Correct Answer: D

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Question 22 View Details

Diffusion of oxygen across a capillary wall follows Fick's law: rate \(= \dfrac{D \; A \; \Delta C}{\Delta x}\). Tissue A has a wall thickness of \(0.5 \;\mu\text{m}\), diffusion coefficient \(D = 2.0 \times 10^{-5}\,\text{cm}^2\text{s}^{-1}\), concentration gradient \(\Delta C = 0.10\ \text{mol cm}^{-3}\) and an effective surface area \(A\). Tissue B has double the surface area of tissue A, a wall thickness of \(1.0 \;\mu\text{m}\) and a concentration gradient of \(0.15\ \text{mol cm}^{-3}\) (same \(D\)). Which tissue provides the higher rate of oxygen diffusion? State the tissue name.

A. Tissue D

B. Tissue A

C. Tissue C

Correct D. Tissue B

Correct Answer: D

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Question 23 View Details

Using the Fick principle, the rate of oxygen consumption (\( \dot V_{O_2}\)) is given by \( \dot V_{O_2}= Q \times (C_{aO_2}-C_{vO_2})\). A person has a cardiac output of \(5\ \text{L min}^{-1}\). Their arterial blood oxygen content is calculated from haemoglobin concentration \(15\ \text{g dL}^{-1}\), arterial oxygen saturation \(97\%\) and arterial \(P_{O_2}=100\ \text{mmHg}\). Venous oxygen content is \(0.12\ \text{ml O}_2\text{ ml}^{-1}\). (Use \(C_{aO_2}= (Hb \times 1.34 \times S_{aO_2}) + 0.0031\,P_{aO_2}\) with \(Hb\) in g dL\(^{-1}\) and \(P_{aO_2}\) in mmHg.) Calculate the whole‑body oxygen consumption in \(\text{ml min}^{-1}\), rounded to the nearest whole number.

A. 350

B. 480

C. 420

Correct D. 390

Correct Answer: D

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Question 24 View Details

A bacterial culture is inoculated with \(1.0 \times 10^{3}\) cells. After a total of 4 h the viable count is \(8.0 \times 10^{5}\) cells. The first hour represents a lag phase with no division; thereafter the culture grows exponentially with a constant generation time. Determine (a) the generation time in minutes, and (b) the expected cell number after 10 h total incubation (including the lag phase). Give your answer for (b) in scientific notation to two significant figures.

Correct A. 5.0×10^{11}

B. 3.2×10^{11}

C. 2.5×10^{11}

D. 1.0×10^{12}

Correct Answer: A

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Question 25 View Details

In a family, an autosomal recessive disorder is present. Both parents are phenotypically normal but each has an affected sibling. Assuming Hardy-Weinberg equilibrium and that the disorder is rare, what is the probability that their first child will be affected? Express your answer as a common fraction.

A. 1/3

B. 1/6

Correct C. 1/9

D. 2/9

Correct Answer: C

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