Paper 2 (topics 5–8)

Name the precise location of the light-independent reaction in a chloroplast.

Describe how glycerate 3-phosphate (GP) is converted to triose phosphate (TP) and how ribulose bisphosphate (RuBP) is regenerated.

Figure 1 shows the rate of photosynthesis of a plant at different light intensities and two CO₂ concentrations. Explain the shape of the curves between 0 and 100 µmol photons m⁻² s⁻¹ and above 400 µmol photons m⁻² s⁻¹.

In a chromatogram of leaf pigments, a pigment travelled 3.2 cm and the solvent front travelled 8.0 cm. Calculate the Rf value and explain how it could identify the pigment.

A herbicide blocks the electron transfer chain in chloroplasts. Suggest why this kills the plant.

Give the net products of glycolysis for each molecule of glucose.

Explain why oxygen is needed for oxidative phosphorylation.

Germinating seeds produced 0.70 cm³ of CO₂ and used 0.98 cm³ of O₂ in the same time. Calculate the respiratory quotient and suggest which respiratory substrate was being used.

In a respirometer containing germinating seeds and potassium hydroxide solution, a coloured liquid moved 25 mm along a capillary tube of radius 0.5 mm in 10 minutes. (a) Explain why the liquid moved towards the seeds. (b) Calculate the rate of oxygen uptake in mm³ min⁻¹. Volume = πr²l.

The gross primary production of grassland is 21 000 kJ m⁻² year⁻¹. Plants use 12 500 kJ m⁻² year⁻¹ in respiration. Calculate the net primary production.

Primary consumers in the grassland have a production of 850 kJ m⁻² year⁻¹. Calculate the efficiency of energy transfer from producers (using NPP) to primary consumers.

Explain one farming practice that increases the efficiency of energy transfer to livestock.

Describe the roles of saprobionts and nitrifying bacteria in the nitrogen cycle.

Describe how a resting potential is maintained in a neurone.

Explain how depolarisation and repolarisation occur during an action potential.

Explain why impulses travel faster along myelinated axons.

Describe how an impulse is transmitted across a cholinergic synapse.

Describe the roles of calcium ions and ATP in muscle contraction.

Give two differences between slow-twitch and fast-twitch muscle fibres.

Explain how glucagon causes an increase in blood glucose concentration, including the role of a second messenger.

Explain the difference in cause between type 1 and type 2 diabetes.

Explain how ADH reduces the volume of urine produced when a person is dehydrated.

In a dihybrid cross the expected ratio was 9 : 3 : 3 : 1. Of 160 offspring, the observed numbers were 85, 31, 28 and 16. Use the chi-squared test to decide whether the results differ significantly from the expected ratio. The critical value for 3 degrees of freedom at p = 0.05 is 7.815.

Haemophilia is caused by a recessive allele on the X chromosome. A carrier woman and an unaffected man have a child. Use a genetic diagram to find the probability that the child is a son with haemophilia.

Cystic fibrosis is caused by a recessive allele. In a population, 4 in every 100 people have the condition. Use the Hardy–Weinberg equation to calculate the percentage of people who are carriers.

Explain how allopatric speciation can occur.

Describe how succession takes place on bare rock.

Explain how oestrogen stimulates transcription of a target gene.

Explain how increased methylation of DNA can reduce the expression of a gene.

Distinguish between totipotent and pluripotent stem cells.

Explain how small interfering RNA (siRNA) prevents translation of a particular mRNA.

Describe the polymerase chain reaction.

Give two uses of genetic fingerprinting.

Suggest two reasons why gene therapy may not provide a long-term cure for a genetic disorder.