GCSE Biology Higher Paper 4

Question 1 [4 marks]

Evolution and Natural Selection

In a population of 5000 ladybirds, 800 have a rare colour pattern that camouflages them well against a newly introduced plant.

After several generations, the number of ladybirds with this colour pattern rises to 3500 in a population that has grown to 8000. Calculate the percentage of the population with this colour pattern before and after this change.

Question 2 [4 marks]

Genetics and Inheritance

In snapdragon plants, flower colour shows codominance. The allele for red flowers (R) and the allele for white flowers (W) are both expressed if present together, producing pink flowers.

A red-flowered plant (RR) is crossed with a white-flowered plant (WW). Use a genetic diagram to determine the genotype and phenotype of all the offspring, and explain why this phenotype appears.

Question 3 [4 marks]

Hormones and Homeostasis

A patient's blood glucose concentration was 5.5 mmol/l at 08:00 and rose to 9.5 mmol/l at 08:30 after breakfast.

Calculate the mean rate of increase in blood glucose concentration, in mmol/l per minute, over this time.

Question 4 [4 marks]

Cell Division and Stem Cells

A single cell divides by mitosis every 20 minutes.

Starting from one cell, calculate how many cells will be present after 2 hours, assuming every cell divides on schedule.

Question 5 [5 marks]

Photosynthesis

A grower measures that one tomato plant produces 40 g of new dry biomass per week under standard greenhouse conditions. Under improved lighting, this rises to 58 g per week.

Calculate the percentage increase in biomass production per plant, and calculate the total extra biomass produced per week across a greenhouse of 250 plants, assuming every plant shows the same increase.

Question 6 [5 marks]

Human Defence Systems and Treating Disease

In a trial, 3% of 2000 vaccinated people caught a disease, compared with 15% of 2000 unvaccinated people.

Calculate the number of people who caught the disease in each group, and calculate the vaccine's efficacy using efficacy (%) = (1 - (rate in vaccinated group / rate in unvaccinated group)) x 100.

Question 7 [5 marks]

Digestion and the Circulatory System

A student tested the activity of pepsin (a protease enzyme found in the stomach) at pH 2 and at pH 8, and found it broke down protein much faster at pH 2.

Explain, in terms of enzyme structure, why pepsin is much less active at pH 8.

Question 8 [5 marks]

Ecosystems and Material Cycles

A student used a transect line across a rocky shore and placed a 0.5 m^2 quadrat every 2 metres along the line. In one quadrat, seaweed covered an estimated 60% of the quadrat's area.

Calculate the area, in m^2, of the quadrat that was covered by seaweed. If the whole study area along the shore covers 400 m^2 and this percentage cover is representative of the whole area, estimate the total area of the shore covered by seaweed.

Question 9 [6 marks]

The Nervous System and Reflexes

A voluntary action, such as deciding to pick up a cup, involves conscious thought, while a reflex action, such as pulling a hand away from something hot, does not.

Explain the difference in the neural pathway between a voluntary action and a reflex action, and explain why this difference makes reflex actions faster.

Question 10 [6 marks]

Pathogens and Communicable Disease

Before a hand-washing campaign in a hospital, 40 out of 800 patients developed a healthcare-associated infection in one month. After the campaign, 12 out of 750 patients developed an infection in one month.

Calculate the percentage of patients infected before and after the campaign, and explain, in terms of pathogen transmission, why improved hand hygiene reduces the spread of infection.

Question 11 [6 marks]

Cell Structure and Transport

The rate of diffusion across an exchange surface is proportional to its surface area and inversely proportional to its thickness.

Membrane A has a surface area of 20 mm^2 and a thickness of 0.04 mm. Membrane B has a surface area of 15 mm^2 and a thickness of 0.05 mm.

Calculate the ratio of surface area to thickness for each membrane, then determine which membrane would allow a faster rate of diffusion, explaining your reasoning.

Question 12 [6 marks]

Respiration and Exercise

A trained athlete and an untrained person perform the same short bout of vigorous exercise. The untrained person builds up an oxygen debt of 8 litres and takes 25 minutes to recover. The trained athlete builds up an oxygen debt of only 5 litres and recovers in 10 minutes.

Calculate each person's mean rate of recovery (oxygen consumed above resting level, in litres per minute), and explain why the trained athlete's oxygen debt is smaller for the same exercise.