Structured Questions (AS & A Level) (AQA A Level Biology): Exam Questions

Exam code: 7402

2 hours9 questions
1a3 marks

Figure 1 represents part of the gas exchange system of an insect.

Figure 1

Diagram showing a cross-section of body tissue. Label A indicates outer body, B marks a tubular structure, and C shows branching connections inside the tissue.

(i) Name the part labelled A in Figure 1.

[1]

(ii) Describe the role of A in insect gas exchange.

[2]

1b4 marks

Identify and explain two features of the insect gas exchange system that maximise the rate of oxygen uptake.

1c3 marks

Insects have an open circulatory system in which a blood-like fluid, called haemolymph, flows freely through the body cavity. A tubular heart located along the back of the insect pumps haemolymph forward in waves. The fluid is released into spaces surrounding the organs, where it directly bathes the tissues. Haemolymph is responsible for transporting nutrients, hormones, and waste products, and for helping to regulate internal conditions.

Explain how the circulatory system of a human differs to that of an insect.

1d3 marks

In very active insects the muscles produce lactate during anaerobic respiration, which drives the movement of water out of the tracheoles and into the muscle cells.

Suggest how lactate production helps to maintain a high rate of oxygen diffusion into muscle cells.

2a2 marks

Researchers studied 241 pet Labradors and discovered a strong link between the gene DENND1B and increased body fat. Dogs with a mutation resulting in overexpression of the DENND1B gene had on average 8% more body fat and showed more food-seeking behaviour than dogs without the mutation. However, not all Labradors carrying the mutation were overweight.

Suggest why not all Labradors with the DENND1B mutation were overweight.

2b2 marks

Describe how overexpression of DENND1B results in increased production of the DENND1B protein.

2c2 marks

One of the key receptors involved in regulating appetite and energy use is the MC4R receptor, a G protein–coupled receptor (GPCR) found in the hypothalamus. MC4R is normally activated by the hormone α-MSH, which triggers a second messenger response leading to:

  • suppressed appetite

  • increased energy expenditure

However, the DENND1B protein can also bind to MC4R, causing internalisation of the receptor—this means that the receptor is removed from the cell surface and brought into the cytoplasm.

Suggest why the MC4R receptor is able to respond to both the DENND1B protein and α-MSH.

2d3 marks

Suggest how internalisation of the MC4R receptors could lead to weight gain.

3a3 marks

Scientists investigated the process of succession on sand dunes. They measured both the biomass of vegetation and the percentage cover of different plant species on sand dunes of different ages. Some of the results the scientists obtained are shown in Figure 1.

Figure 1

Graph showing biomass, grass, shrubs, and tree cover over 100 years of succession; biomass and tree cover increase, grass and shrubs decrease.

Describe the evidence in Figure 1 that shows succession is taking place.

3b2 marks

Explain how light intensity at ground level may change over the time period in Figure 1.

3c3 marks

The scientists measured changes in plant biomass over time.

(i) Suggest how biomass for the area being studied could be estimated.

[2]

(ii) Explain whether the scientists are likely to have measured NPP or GPP.

[1]

3d2 marks

Describe how the scientists could have estimated the percentage cover of the plant species.

4a2 marks

Oestrogen is a steroid hormone that plays a key role in the female reproductive system. Steroid hormones are nonpolar molecules.

Explain why steroid hormones like oestrogen can easily pass through the membrane of a target cell.

4b3 marks

Oestrogen affects the transcription of target genes in certain cells.

Explain how oestrogen increases the rate of transcription of these genes.

4c2 marks

Explain how high oestrogen levels could increase the risk of cancer in post-menopausal women.

4d2 marks

Describe two differences between benign and malignant tumours.

5a1 mark

CRISPR-Cas9 is a gene-editing technology that uses an enzyme called Cas9, to cut DNA at a specific point, allowing genes to be removed, added, or altered within an organism's genome.

Define the term genome.

5b3 marks

Scientists have used CRISPR-Cas9 gene editing to successfully remove HIV DNA from infected human cells in laboratory settings.

Describe how HIV DNA becomes incorporated into human DNA after infection.

5c6 marks

Once HIV DNA is integrated into the host genome, it can be used to produce viral proteins.

Describe the processes that lead to the production of these proteins.

5d2 marks

HIV produces long polyproteins that must be cut into smaller sections in order to assemble the capsid and enzymes in new viral particles.

Suggest how antiretroviral treatments (ARTs) that contain a protease inhibitor might prevent new viral particles from assembling.

5e1 mark

Suggest one reason why CRISPR-Cas9 provides a better treatment for people with HIV than ART.

6a3 marks

Cystic fibrosis (CF) is an inherited disorder caused by mutations in the CFTR gene, which encodes a membrane protein that helps regulate chloride ion transport in epithelial cells.

In healthy individuals chloride ions (Cl⁻) are transported out of the epithelial cells and into the mucus that lines the body’s inner surfaces. In those suffering from CF the chloride ion transport protein is faulty.

Explain how a mutation in the CFTR gene could lead to production of a non-functional protein.

6b2 marks

Cystic fibrosis affects the epithelial cells lining the lungs and digestive system, leading to the production of thick and sticky mucus.

Suggest how a faulty CFTR protein results in the production of thick, sticky mucus.

6c3 marks

Scientists have proposed treating CF using gene therapy. This involves inserting a functional copy of the CFTR gene into epithelial cells.

Explain why this method could reduce symptoms of CF.

6d5 marks

The pedigree diagram in Figure 1 shows the inheritance of cystic fibrosis across 3 generations.

Figure 1

biology-3-3-q7-ib-hl-

(i) Identify the genotype of the individuals labelled 1, 2 and 3 in the pedigree diagram and explain your answer.

[2]

(ii) Two out of three of the children of individuals 1 and 2 have CF.

Use a Punnet square to compare this to the expected ratios predicted for offspring from individuals 2 and 3.

[2]

7a3 marks

A team of ecologists investigated the recovery of a sand dune ecosystem after a storm destroyed much of the vegetation. They measured plant species diversity and net primary productivity (NPP) at intervals over a 20 year period.

For each round of sampling the ecologists overlaid a numbered grid onto a map of the 2-hectare (20 000 m2) site and used a random number generator to select 50 separate 1 m2 quadrat locations. During data collection they:

  • identified all plant species in each quadrat and calculated an index of diversity (d)

  • estimated the percentage cover of marram grass by visual assessment, using a gridded quadrat frame to improve accuracy

  • harvested all above-ground plant material from each quadrat, oven-dried it to constant mass, and used this to estimate NPP (g m⁻² year⁻¹)

All sampling was conducted in the same fortnight each year, on dry, sunny days. The sheltered side of the dune system was avoided to minimise shelter effects from nearby woodland. Table 1 shows their results.

Table 1

Years since storm

Mean index of diversity (d)

Mean NPP / g m⁻² year⁻¹

Standard deviation of NPP / g m⁻² year⁻¹

2

0.84

210

15

5

1.56

430

21

12

2.31

610

34

20

2.45

685

39

Explain the change in diversity between years 2 and 20.

7b4 marks

Figure 1 shows the percentage cover of marram grass (Ammophila arenaria) over the course of the study.

Figure 1

Line graph showing percentage cover of marram grass over time. Peaks at 5 years with 70%, then declines to 20% at 20 years after a storm.

(i) Suggest an explanation for the trend in marram grass cover shown in Figure 1.

[2]

(ii) The ecologists concluded that changes in marram grass cover affected NPP in the sand dune ecosystem. Use the information provided to evaluate this conclusion.

[4]

7c3 marks

Marram grass contains chlorophyll a, chlorophyll b and carotenoids.

Describe the role of these molecules in photosynthesis.

7d2 marks

Figure 2 shows a cross-section through a marram grass leaf taken using a light microscope.

The labelled structures are:

  • X = the outer surface of the leaf

  • Y = the position of a stoma

  • Z = a leaf hair

Figure 2

Cross-section of a plant stem under a microscope, showing labelled regions marked X, Y, Z.

Berkshire Community College, via Wikimedia Commons (opens in a new tab)

Suggest how the features visible in Figure 2 reduce water loss while allowing photosynthesis to continue.

7e3 marks

Explain how the adaptive features of marram grass have evolved.

8a2 marks

Tetrodotoxin (TTX) is a neurotoxin produced in the bodies of some marine organisms. TTX binds to an extracellular site on voltage-gated sodium ion channels (VGSCs) in the membranes of axons, preventing the passage of sodium ions.

Explain how exposure to TTX would affect nerve impulses.

8b
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4 marks

Scientists looked at the effectiveness of TTX in the relief of long-term (chronic) nerve pain in adults. 150 participants were randomly assigned to receive one of the following:

  1. a placebo (containing no active ingredient) by subcutaneous injection for 7 days

  2. low-dose TTX by subcutaneous injection for 7 days

  3. high-dose TTX by subcutaneous injection for 7 days

Pain was recorded on a 0–10 numerical rating scale (NRS) each evening. A responder was defined as an individual with ≥30% reduction from baseline pain levels. The results from study 1 are shown in Table 1 below.

Table 1

Treatment

Baseline NRS

Mean NRS during days 1–7

Responders / 50 participants

Placebo

7.1 ± 0.6

6.2 ± 0.7

14 / 50

Low-dose TTX

7.0 ± 0.6

5.4 ± 0.7

21 / 50

High-dose TTX

7.1 ± 0.5

4.8 ± 0.5

27 / 50

(i) Explain the role of the placebo treatment in the study.

[2]

(ii) Calculate the difference in the percentage decrease in pain between patients receiving a placebo and patients receiving a high dose of TTX.

[2]

8c4 marks

Voltage-gated sodium channel (VGSC) proteins occur in several subtypes. Some are termed TTX-sensitive (TTX-S) because tetrodotoxin binds to them strongly at low concentrations. Others are TTX-resistant (TTX-R) because tetrodotoxin has a much lower affinity for them at the same concentration.

In chronic pain after nerve injury, the pattern of VGSC gene expression in pain-sensing neurones often changes: TTX-S subtypes are upregulated, and TTX-R subtypes are commonly downregulated in the injured neurones.

(i) Explain how expression of TTX-S VGSC genes could be upregulated.

[2]

(iii) Suggest why TTX can reduce chronic pain levels, as shown in Table 1.

[2]

8d7 marks

Eating improperly prepared pufferfish can result in TTX poisoning. Numbness develops around the mouth, followed by widespread muscle weakness. Within two hours poisoned individuals are unable to breathe without assistance.

(i) Explain how TTX poisoning can result in muscle weakness and paralysis.

[3]

(ii) Even in severe cases of TTX poisoning, a heart rhythm may persist.

Suggest why normal heart rhythms continue despite TTX poisoning.

[2]

(iii) In some cases of TTX poisoning, doctors may administer acetylcholinesterase inhibitors, such as the drug neostigmine.

Suggest how neostigmine may help to restore ventilation.

[2]

9a2 marks

A group of researchers studied ATP production in isolated mitochondria from mammalian skeletal muscle. They prepared a series of solutions containing mitochondria, ADP and inorganic phosphate. They then added different substrates in order to alter the products of the Krebs cycle; either:

  1. pyruvate + malate: NADH is generated during the Krebs cycle

  2. succinate: FADH₂ is generated during the Krebs cycle

State the role of NADH and FADH2 in the mitochondria.

9b7 marks

The scientists wanted to assess the impact of NADH and FADH2 on the electron transport chain, shown in Figure 1 below.

Figure 1

Diagram of the electron transport chain in the mitochondrial inner membrane, showing Complexes I-IV, CoQ, Cyt c, and ATP synthase.

They added each of the following compounds separately to solutions 1 and 2:

  • Rotenone (inhibits complex I)

  • Antimycin A (inhibits complex III)

  • Oligomycin (inhibits ATP synthase)

For each of the following experimental conditions, use all of the information provided to predict and explain the effect on oxygen consumption and ATP synthesis.

(i) Pyruvate + malate with rotenone

[2]

(ii) Succinate with rotenone

[2]

(iii) Succinate with oligomycin

[3]

9c4 marks

Figure 1 above shows the location of a protein known as cytochrome C, or cyt C, which forms part of the electron transport chain. The DNA sequence of the gene that codes for cytochrome c is very similar in many different organisms, although small differences do occur.

(i) Suggest why the DNA sequence of the gene that codes for cytochrome c is so similar across many different organisms.

[2]

(ii) Suggest one advantage and one limitation of using cytochrome C to investigate relationships between species.

[2]

9d5 marks

One mechanism by which the DNA base sequence for cytochrome C can be determined involves gel electrophoresis.

(i) Describe the process of gel electrophoresis.

[4]

(ii) Identify one application of gel electrophoresis, other than determining DNA base sequence.

[1]