Paper 2 (topics 5–8)

Calvin supplied algae with radioactive ¹⁴CO₂ for very short times. Explain why GP was the first radioactive compound detected and TP second.

A grower raises CO₂ concentration and temperature in a greenhouse. Explain how this increases yield and why heating to very high temperatures would not help.

Describe oxidative phosphorylation.

The respiratory quotient (RQ) of germinating castor oil seeds is 0.7. What does this suggest? Explain.

Explain why production of lactate allows glycolysis to continue in anaerobic conditions.

Producers have a net production of 20 000 kJ m⁻² year⁻¹ and primary consumers 1 600 kJ m⁻² year⁻¹ (data are illustrative, written for this paper). Calculate the efficiency of energy transfer and give two reasons why it is low.

Explain how keeping livestock indoors increases the efficiency of energy transfer.

Describe the roles of bacteria in the nitrogen cycle.

Describe a simple reflex arc and explain its importance.

Explain why the threshold of a receptor allows the body to ignore very weak stimuli.

Explain how a rise in blood pressure is detected and corrected.

Explain the importance of the refractory period.

Explain what is meant by the 'all-or-nothing' principle.

Explain spatial and temporal summation at synapses.

Some insecticides inhibit acetylcholinesterase. Explain how this affects the insect's muscles.

Explain the changes in the bands of a sarcomere when a muscle contracts.

Explain the role of phosphocreatine in muscle contraction.

Describe how adrenaline increases blood glucose concentration using the second messenger model.

Explain how the loop of Henle helps produce concentrated urine.

Explain why homeostasis is important for enzyme activity.

In mice, gene A is needed for coat colour (A coloured, a albino), and gene B determines colour (B black, b brown). aa mice are albino whatever their B alleles. Two AaBb mice are crossed. Give the expected phenotypic ratio and explain it.

Explain how sympatric speciation can occur.

Explain why genetic drift has a greater effect in small populations.

Explain how induced pluripotent stem cells (iPS cells) are produced.

Explain how transcription factors control gene expression.

Name two types of gene mutation other than substitution and deletion.

Explain how restriction enzymes and ligase are used to insert a gene into a plasmid.

Explain how gel electrophoresis separates DNA fragments in genetic fingerprinting.

Explain one benefit of the Human Genome Project for medicine.

Comprehension passage (written for this paper): CAR-T cell therapy. (1) Some leukaemias are cancers of B lymphocytes. (2) In CAR-T therapy, T cells are removed from a patient's blood. (3) A gene coding for a chimeric antigen receptor (CAR) is inserted into the T cells using a harmless virus. (4) The CAR is complementary to CD19, a protein found on the surface of B cells. (5) The modified T cells are multiplied in the laboratory and returned to the patient. (6) In one trial, 63 of 75 patients showed no detectable cancer after three months. (7) However, the treatment also destroys healthy B cells, and some patients develop a severe inflammatory reaction. Explain why T cells with the CAR destroy B cells (sentences 3 and 4).

Explain why a virus can be used to insert the CAR gene into T cells.

Calculate the percentage of patients with no detectable cancer after three months (sentence 6).

Suggest why destroying healthy B cells (sentence 7) is a problem and how doctors might reduce the harm.

Evaluate CAR-T therapy as a treatment for leukaemia.