Biology Exam Practice Questions and Model Answers

1. Homeostasis and Ecology

• 1(a) Maintaining constant internal conditions.
• 1(b) 250 hours.
• 1(c)(i) A.
• 1(c)(ii) Fertilisers from farms run off into rivers. This causes algal growth. Less light penetrates, reducing photosynthesis. Pesticides kill organisms.
• 1(d)(i) Low FSH: eggs do not mature.
• 1(d)(ii) Low LH: no ovulation.
• 1(e)(i) Less water is absorbed into the blood. Water moves by osmosis because water potential remains higher in the blood.
• 1(e)(ii) Mutation. Only resistant bacteria survive. They reproduce and pass on the allele.
• 1(f)(i) Denitrifying bacteria convert nitrate to nitrogen gas. This reduces algal growth, so there is more oxygen in rivers.
• 1(f)(ii) Roots absorb water. More transpiration occurs, leading to slower water flow and less runoff.

2. Respiratory and Renal Systems

• 2(a)(i) B.
• 2(a)(ii) The diaphragm contracts and flattens; the ribcage moves up and out; lung volume increases and pressure falls, so air enters.
• 2(b) Glucose in urine. There is too much glucose to reabsorb. It is normally reabsorbed in the PCT by active transport.

3. Sensory Perception

• 3(a) A.
• 3(b)(i) 8.2.
• 3(b)(ii) Pupil diameter decreases; the biggest decrease occurs between 2–3 au.
• 3(b)(iii) Less light enters to prevent retina damage. Circular muscles contract; radial muscles relax.
• 3(b)(iv) Same distance from the camera.
• 3(b)(v) Use a camera image; wait 20 seconds so the pupil stops changing.

4. Cloning and Genetics

• 4(a) Diploid cell; egg cell; electric shock; mitosis; uterus.
• 4(b) Low success rate; cattle have the highest survival, goats the lowest; cloning is expensive; clones are genetically identical, so harmful alleles are passed on; not all traits are genetic.

5. Plant Physiology

• 5(b)(i) 8.16.
• 5(b)(ii) Cut the stem underwater; use a fan at different distances; leave for a set time; measure bubble movement; control variables; repeat.
• 5(c) At the start, ABA is low and water loss is high. After two days, ABA increases and water loss decreases. After watering, ABA decreases and water loss increases. As ABA increases, water loss decreases because ABA closes stomata.

6. Enzymes and Methodology

• 6(a)(i) 1400%.
• 6(a)(ii) Optimum pH is 7. Away from the optimum, the enzyme denatures. The active site changes shape so the substrate no longer fits.
• 6(a)(iii) Use a light sensor because colour change is subjective and needs standardising. Check more often.
• 6(b)(i) DNA is double-stranded, RNA is single-stranded. DNA has thymine (T), RNA has uracil (U). DNA has deoxyribose, RNA has ribose.