Paper 1 (topics 1–4)

Describe how a peptide bond is formed between two amino acids.

Explain how a change in the primary structure of an enzyme could stop it working.

Figure 1 shows the rate of an enzyme-controlled reaction at different substrate concentrations, with and without an inhibitor. Use Figure 1 to identify the type of inhibitor and explain your answer.

In an electron micrograph, a mitochondrion is 36 mm long. The scale bar shows that 20 mm represents 1 µm. Calculate the actual length of the mitochondrion.

Describe and explain how cell fractionation and ultracentrifugation can be used to obtain a sample of mitochondria.

Give three structural differences between a prokaryotic cell and a eukaryotic cell.

In a root tip squash, 24 of 160 cells were in a stage of mitosis. Calculate the mitotic index as a percentage.

A student placed potato cylinders in sucrose solutions and recorded the percentage change in mass (Figure 2). Use Figure 2 to estimate the water potential of the potato tissue as a sucrose concentration, and explain how you used the graph.

Explain why the student calculated percentage change in mass rather than change in mass.

Explain why the cell-surface membrane is described as a fluid mosaic.

Describe the principles of an ELISA test used to detect a viral antigen in a blood sample.

Explain why antibiotics are not effective against HIV.

Explain how vaccinating a large proportion of a population can protect people who have not been vaccinated.

Explain how the counter-current flow in fish gills makes gas exchange efficient.

A person has a tidal volume of 0.5 dm³ and a breathing rate of 14 breaths per minute. Calculate their pulmonary ventilation, giving units.

Explain how insects limit water loss while still exchanging gases efficiently.

Describe the role of micelles in the absorption of lipids.

Figure 3 shows oxygen dissociation curves for haemoglobin at two different carbon dioxide concentrations. Identify which curve shows the higher concentration of carbon dioxide and explain the advantage of this shift to respiring tissues.

Use Figure 3 to find the difference in percentage saturation between curves A and B at a partial pressure of 4 kPa.

Describe what happens to the atrioventricular and semilunar valves when the ventricles contract, and explain why.

Explain how tissue fluid is formed at the arteriole end of a capillary.

Describe how a polypeptide is produced during translation.

Explain what is meant by the genetic code being degenerate and non-overlapping.

A polypeptide has 150 amino acids. Calculate the minimum number of nucleotides in the mature mRNA that codes for it, including the stop codon, and explain why the gene is longer.

Explain why a substitution mutation may have no effect on the protein produced.

Explain how meiosis produces genetic variation.

An organism has a diploid number of 8. How many different combinations of chromosomes can result from independent segregation alone?

Explain how directional selection could lead to an increase in the frequency of an allele for pesticide resistance in an insect population.

In a woodland survey, a student found 12 bluebells, 6 primroses and 2 orchids. Calculate the index of diversity using d = (N(N - 1))/(Σ n(n - 1)).

Explain how the use of genome sequencing has changed how scientists classify species.

Explain how courtship behaviour helps an animal to reproduce successfully.

Describe and explain how the structure of the plasma membrane, and of the cells lining the ileum, allow glucose to be absorbed into the blood. (Level of response: 6 marks for the description, plus 4 marks for explanation and use of terminology.)