AQA A Level Biology Paper 2 June 2023 question paper 7402/2

A student used chromatography to separate the different photosynthetic pigments in a chlorophyll solution. She had the following materials.

Chromatography paper A ruler and pencil Suitable glassware A solvent (solvent A)

Describe how she could use these materials to separate the photosynthetic pigments by chromatography.

Using solvent A, the student separated five pigments. She then repeated her method using a different solvent, B. Using solvent B, she separated six pigments.

Explain the difference between these results.

Glutamate is a neurotransmitter involved in the transmission of nerve impulses from pain receptors to the brain. Ziconotide is a drug that can reduce severe, constant pain. Ziconotide blocks the calcium ion channels at some of the synapses which use glutamate.

The transmission of glutamate at synapses is similar to that of acetylcholine.

Explain how ziconotide reduces severe, constant pain.

Ziconotide is a polypeptide and acts on synapses in the spinal cord. Scientists investigated the effectiveness of ziconotide in reducing severe, constant pain.

Ziconotide was injected into each patient’s cerebrospinal fluid that bathes the brain and spinal cord. Patients recorded the intensity of their pain using a statistically valid scale.

Suggest two reasons why the patients had ziconotide injected into their cerebrospinal fluid rather than taking a pill containing the drug.

Ziconotide was injected at 3 ng kg^–1 h^–1 for 8 days into each patient.

Calculate the total mass in grams of ziconotide injected after 8 days into a patient with a body mass of 82 kg

Show your working.

When the patients recorded the intensity of pain, suggest two reasons why it was important to use a statistically valid scale.

Figure 1 shows part of a phosphorus cycle, including the mass of phosphorus in two stores.

One teragram (Tg) is 1 × 10¹² grams.

The supply of phosphorus to the soil is shown as a percentage of the total phosphorus mass of each store.

Calculate in teragrams the difference in the supply of phosphorus to the soil from the two stores shown in Figure 1.

Show your working.

Water shortage can inhibit crop production. Scientists investigated the effect of the mycorrhizal species Glomus intraradices on the growth of tomato plants under conditions of water shortage and no water shortage.

• The scientists planted tomato seeds into a large number of pots containing sterilised soil.

• They added a culture of G. intraradices to 50% of the pots and 50% were left untreated.

• After the seeds had developed into seedlings (young plants), the seedlings from the untreated and treated pots were planted into four separate large greenhouses (glasshouses).

• A very limited supply of water (water shortage) was provided to two of the greenhouses. A sufficient supply of water (no water shortage) was provided to the other two greenhouses.

• After 60 days, the scientists determined the mean mass of tomatoes (kg m^–2) from each greenhouse.

Greenhouse P – untreated seedlings with water shortage Greenhouse Q – treated seedlings with water shortage Greenhouse R – untreated seedlings with no water shortage Greenhouse S – treated seedlings with no water shortage

Treated seedlings are plants grown with G. intraradices.

Figure 2 shows the scientists’ results.

The error bars represent ± 2 standard deviations from the mean, which includes over 95% of the data.

Using all the information, evaluate the effectiveness of using mycorrhizae to increase crop production under conditions of water shortage and no water shortage.

The tomato seeds were planted into sterilised soil.

Suggest two reasons why the soil was sterilised.

The soil used in this investigation had the recommended concentration of fertiliser.

Suggest two reasons why the soil contained the recommended concentration of fertiliser.

In cats, males are XY and females are XX. A gene on the X chromosome controls fur colour in cats. The allele G codes for ginger fur and the allele B codes for black fur. These alleles are codominant. Heterozygous females have ginger and black patches of fur and their phenotype is described as tortoiseshell female.

The two alleles, F and f of a different gene, which is not sex-linked, interact with the gene controlling fur colour. The allele F is dominant and stops the formation of pigment in the fur, resulting in white fur. The allele f is recessive and has no effect on fur colour.

Name the type of interaction between the two genes affecting fur colour.

What phenotype would a cat with the following genotype have?

Complete the genetic diagram to show all the possible genotypes and the ratio of phenotypes expected in the offspring of this cross.

Phenotypes of parents X^GX^GFf x X^BYff

Ratio of offspring phenotypes

In a population, 36% of cats had the F allele and had white fur.

Use the Hardy–Weinberg equation to calculate the frequency of the f allele in this population.

Show your working.

Figure 3 shows the wavelengths of light absorbed by three types of photoreceptor found in the human retina.

Use Figure 3 and your knowledge of colour vision to explain how an orange colour is seen at 600 nm

Which of the following statements is associated with high sensitivity to light in the retina?

Tick (✓) one box.

Variation in flower colour is considered one of the factors involved in the evolution of the following two species of monkeyflower.

• Erythranthe lewisii (Great Purple Monkeyflower), which has pink flowers, is mostly found at higher altitudes (1600 to 3000 metres) and attracts bumblebees.

• Erythranthe cardinalis (Scarlet Monkeyflower), which has red flowers, is mostly found at lower altitudes (up to 2000 metres) and attracts hummingbirds.

Bumblebees and hummingbirds are important in the pollination of flowers. Pollination involves the transfer of male gametes to female gametes.

Explain the different processes that may have been involved in the evolution of these two species of monkeyflower. Use the information provided to justify your answer.

Describe and explain how three features of the cells in the proximal convoluted tubule allow the rapid reabsorption of glucose into the blood.

Antidiuretic hormone (ADH) binds to V receptors found in cell-surface membranes in two parts of a nephron.

Name the two parts of a nephron where V receptors are found.

V receptors only bind with ADH.

Suggest and explain why.

A decrease in blood pressure stimulates the release of ADH.

Give the location of the receptors that detect a decrease in blood pressure and explain how the release of ADH will affect blood pressure.

In the following passage, the numbered spaces can be filled with biological terms.

An ecosystem supports a certain size of population of a species, called

Write the correct biological term beside each number below that matches the space in the passage.

Suggest two reasons for conserving rainforests.

Give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem.

The KRAS gene codes for a protein called K-Ras. The protein relays signals from outside a cell to a cell’s nucleus, stimulating cell division. An alteration in the KRAS gene produces an oncogene which can cause a tumour to develop.

Suggest and explain how an alteration in the KRAS gene can cause a tumour to develop.

Alterations in the KRAS gene can cause colorectal cancer (CRC). Scientists investigated the survival time of the following three groups of CRC patients who had type II diabetes.

Group A – received no drug to treat type II diabetes Group B – received the drug metformin to treat type II diabetes Group C – received a combination of drugs (including metformin) to treat type II diabetes

The scientists used a statistical test to compare the survival time of these patients with CRC patients with no history of type II diabetes.

Table 1 shows some of the results obtained by the scientists.

Using the information provided, what can you conclude about the effects of type II diabetes and the different drug treatments on the survival time of CRC patients?

Short tandem repeats (STRs) are short sequences of DNA, usually 2 to 7 base pairs. STRs are repeated a number of times, one after another. For example, the STR D5S818 is made up of AGAT repeated 7 to 16 times.

STRs are found throughout the whole genome.

The repeated sequences in STRs are common to all humans. Due to variation in the number of repeats, STRs can be used in genetic fingerprinting.

Describe how STRs could be removed from a sample of DNA.

Genetic fingerprinting using STRs requires amplification of the STRs using the polymerase chain reaction (PCR). The short base sequences either side of a specific STR are known.

Explain the importance of knowing these base sequences in PCR.

A single STR molecule consisting of a 12 base pair sequence of AGAT was amplified 50 times using PCR.

Calculate the total number of base pairs in all the STR molecules after 50 cycles of PCR.

Show your working.

During genetic fingerprinting, the different STRs are separated by gel electrophoresis.

Give two features of STRs which enable them to be separated by gel electrophoresis.

ATP is essential for muscle contraction (line 1).

Describe the roles of ATP in muscle contraction.

Calculate how long maximum exercise would last if ATP was not resynthesised (lines 3–4).

Describe and explain how taking creatine supplements (lines 5–6) and ‘carbohydrate loading’ (lines 6–7) can improve performance of different types of muscle fibres during different types of exercise.

Suggest and explain how GLUT4 and CD36 transport proteins (lines 10–11) are beneficial during exercise.

An increase in muscle activity causes an increase in heart rate (lines 12–14).

Describe and explain how.