15. Control and coordination
A section of Biology, 9700
Listing 10 of 130 questions
shows a section through a maize fruit. A B C D Name the parts labelled A to D. A B C D Describe the function of the endosperm. The corn earworm, is the larva of a moth Helicoverpa zea, that is a serious pest of maize. Insecticides containing pyrethrum have long been used to control this insect. These act by irreversibly inhibiting the enzyme acetylcholinesterase, which normally catalyses the hydrolysis of acetylcholine. Describe how an insecticide could irreversibly inhibit acetycholinesterase. Suggest the effects on synapses of this irreversible inhibition of acetylcholinesterase. Some populations of H. zea have developed resistance to pyrethrum. This occurs as the result of a point mutation of the acetylcholinesterase gene. Many different such mutations have been identified in different populations. Explain how a point mutation in the acetylcholinesterase gene could confer resistance to pyrethrum. • A group of corn earworms was collected from a field where the farmer had reported resistance to insecticides containing pyrethrum. • Another group was collected from a field where the insects showed no resistance (were susceptible). • Some individuals from these two groups were crossed with each other to form a hybrid group. Insects from each of the three groups were then exposed to a range of concentrations of pyrethrum. The percentage of the insects that were dead after 24 hours was recorded. The results are shown in Table 4.1. Table 4.1 dose of insecticide / g per group % mortality of insects after 24 hours resistant group hybrid group susceptible group 0.1 0.5 1.5 2.5 5.0 10.0 30.0 With reference to Table 4.1, compare the effect of the insecticide on the resistant group and on the hybrid group. Assuming that resistance is conferred by a single point mutation in the gene for acetycholinesterase, suggest an explanation for the overall differences between all three groups of insects in Table 4.1.
9700_s09_qp_4
THEORY
2009
Paper 4, Variant 0
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Wheat, Triticum aestivum, owes its origin to hybridisation involving three different, but related, species of grass, A, B and C. Each of these species had seven pairs of chromosomes (2n = 14). The hybridisation process is shown in . species A 2n = 14 (AA) species B 2n = 14 (BB) sterile hybrid 2n = 14 (AB) × Y fertile hybrid 2n = 28 (AABB) species C 2n = 14 (CC) A = one set of chromosomes from species A B = one set of chromosomes from species B Key: C = one set of chromosomes from species C sterile hybrid 2n = 21 (ABC) × Z fertile T. aestivum 2n = 42 ( ) Using the symbols in the key, complete by writing in the chromosome sets of T. aestivum. At the points labelled Y and Z in the hybridisation process, a fertile hybrid was produced from a sterile hybrid. Explain why the hybrid (AB) is sterile and what occurred at the point labelled Y in . In 2012, permission was granted for a field trial in the UK of genetically modified T. aestivum. The wheat carries a gene, taken from peppermint plants, that results in the wheat leaves releasing a volatile, non-toxic chemical, (E)-β-farnesene (Eβf), into the atmosphere. Eβf is not only produced by various species of plants. It is also secreted by aphids when they are disturbed by a predator. Two experiments have been performed into the effect of Eβf on the behaviour of aphids feeding on leaves in closed containers. Experiment 1 Either 10 cm3 of air from a syringe that contained plant leaves that secrete Eβf or 10 cm3 of air from a syringe with no such leaves was added to the containers of feeding aphids. Experiment 2 Either 20 cm3 of air containing 50ng of Eβf or 20 cm3 of air containing no Eβf was added to the containers of feeding aphids. In both experiments, the number of aphids that stopped feeding and moved away from the food leaves was counted. The results are shown in Table 3.1. Table 3.1 Experiment 1 Experiment 2 air added to containers of feeding aphids 10 cm3 air that had been in contact with leaves secreting Eβf 10 cm3 air that had not been in contact with leaves secreting Eβf 20 cm3 air containing 50ng Eβf 20 cm3 air containing no Eβf number of aphids in containers number of aphids that stopped feeding and moved away from the food leaves Discuss the extent to which the results of these experiments support the idea that Eβf is an alarm signal for aphids. Other experiments show that Eβf attracts predators of aphids, such as ladybirds. Explain how growing genetically modified wheat secreting Eβf could increase the yield of wheat. Suggest why growing this genetically modified wheat might be acceptable to people who object to the growth of genetically modified insect-resistant maize or cotton.
9700_s14_qp_41
THEORY
2014
Paper 4, Variant 1
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Wheat, Triticum aestivum, owes its origin to hybridisation involving three different, but related, species of grass, A, B and C. Each of these species had seven pairs of chromosomes (2n = 14). The hybridisation process is shown in . species A 2n = 14 (AA) species B 2n = 14 (BB) sterile hybrid 2n = 14 (AB) × Y fertile hybrid 2n = 28 (AABB) species C 2n = 14 (CC) A = one set of chromosomes from species A B = one set of chromosomes from species B Key: C = one set of chromosomes from species C sterile hybrid 2n = 21 (ABC) × Z fertile T. aestivum 2n = 42 ( ) Using the symbols in the key, complete by writing in the chromosome sets of T. aestivum. At the points labelled Y and Z in the hybridisation process, a fertile hybrid was produced from a sterile hybrid. Explain why the hybrid (AB) is sterile and what occurred at the point labelled Y in . In 2012, permission was granted for a field trial in the UK of genetically modified T. aestivum. The wheat carries a gene, taken from peppermint plants, that results in the wheat leaves releasing a volatile, non-toxic chemical, (E)-β-farnesene (Eβf), into the atmosphere. Eβf is not only produced by various species of plants. It is also secreted by aphids when they are disturbed by a predator. Two experiments have been performed into the effect of Eβf on the behaviour of aphids feeding on leaves in closed containers. Experiment 1 Either 10 cm3 of air from a syringe that contained plant leaves that secrete Eβf or 10 cm3 of air from a syringe with no such leaves was added to the containers of feeding aphids. Experiment 2 Either 20 cm3 of air containing 50ng of Eβf or 20 cm3 of air containing no Eβf was added to the containers of feeding aphids. In both experiments, the number of aphids that stopped feeding and moved away from the food leaves was counted. The results are shown in Table 3.1. Table 3.1 Experiment 1 Experiment 2 air added to containers of feeding aphids 10 cm3 air that had been in contact with leaves secreting Eβf 10 cm3 air that had not been in contact with leaves secreting Eβf 20 cm3 air containing 50ng Eβf 20 cm3 air containing no Eβf number of aphids in containers number of aphids that stopped feeding and moved away from the food leaves Discuss the extent to which the results of these experiments support the idea that Eβf is an alarm signal for aphids. Other experiments show that Eβf attracts predators of aphids, such as ladybirds. Explain how growing genetically modified wheat secreting Eβf could increase the yield of wheat. Suggest why growing this genetically modified wheat might be acceptable to people who object to the growth of genetically modified insect-resistant maize or cotton.
9700_s14_qp_43
THEORY
2014
Paper 4, Variant 3
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Adult Drosophila fruit flies feed on yeasts on the surface of ripe fruits. Female flies lay their eggs inside the fruit and the larvae feed inside the fruit before developing into adults. The tree Morinda citrifolia produces fruits called noni fruits. Noni fruits contain a toxin and are avoided by nearly all Drosophila species, including Drosophila yakuba in mainland Africa. One population of D. yakuba lives on the island of Mayotte off the coast of Africa. The population of D. yakuba on Mayotte has specialised to feed on noni fruit. Flies of this population produce enzymes that give them resistance to the toxin in noni fruits. Adults are able to feed on yeasts on the fruit surface and their eggs and larvae can develop and grow inside the fruit. Scientists have used bioinformatics to estimate that the unique D. yakuba population on Mayotte originated in the last 30 000 years. Describe how a population of Drosophila can develop resistance to noni fruit toxin. Explain why living on an island increases the likelihood of the noni toxin-resistant population of D. yakuba on Mayotte becoming a separate species to the mainland population of D. yakuba. Suggest how scientists can use bioinformatics to estimate the length of time that the population of D. yakuba has been living on Mayotte.
9700_s18_qp_42
THEORY
2018
Paper 4, Variant 2
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The leaves of Mimosa pudica plants are made of a number of structures known as pinnae. The pinnae fold when the leaf is touched. This closes the leaf. shows an open leaf of M. pudica before it is touched. shows the same leaf that has closed after being touched. A open (not touched) pinnae B closed A touch stimulus to an M. pudica leaf causes an action potential to be generated. The action potential results in changes in cells, which cause the leaf to close. shows the mechanism in M. pudica cells that causes the leaf to close. action potential after touch stimulus protons pumped into extensor cells Cl − and K+ ions move out of cells water moves out of cells by osmosis cells become flaccid The leaves of M. pudica and the leaves of Venus fly traps move in response to touch stimuli, but the mechanisms that cause the responses are different. Describe the differences between the mechanism shown in and the mechanism that causes the closure of the modified leaves in Venus fly traps. The rate of photosynthesis decreases by 40% when the leaves of M. pudica close. Explain why the rate of photosynthesis decreases when the leaves of M. pudica close. Plants can carry out cyclic photophosphorylation and non‑cyclic photophosphorylation during the light‑dependent stage of photosynthesis. These processes occur at the grana of chloroplasts. Outline the similarities and differences between cyclic photophosphorylation and non‑cyclic photophosphorylation.
9700_w24_qp_41
THEORY
2024
Paper 4, Variant 1
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The leaves of Mimosa pudica plants are made of a number of structures known as pinnae. The pinnae fold when the leaf is touched. This closes the leaf. shows an open leaf of M. pudica before it is touched. shows the same leaf that has closed after being touched. A open (not touched) pinnae B closed A touch stimulus to an M. pudica leaf causes an action potential to be generated. The action potential results in changes in cells, which cause the leaf to close. shows the mechanism in M. pudica cells that causes the leaf to close. action potential after touch stimulus protons pumped into extensor cells Cl − and K+ ions move out of cells water moves out of cells by osmosis cells become flaccid The leaves of M. pudica and the leaves of Venus fly traps move in response to touch stimuli, but the mechanisms that cause the responses are different. Describe the differences between the mechanism shown in and the mechanism that causes the closure of the modified leaves in Venus fly traps. The rate of photosynthesis decreases by 40% when the leaves of M. pudica close. Explain why the rate of photosynthesis decreases when the leaves of M. pudica close. Plants can carry out cyclic photophosphorylation and non‑cyclic photophosphorylation during the light‑dependent stage of photosynthesis. These processes occur at the grana of chloroplasts. Outline the similarities and differences between cyclic photophosphorylation and non‑cyclic photophosphorylation.
9700_w24_qp_43
THEORY
2024
Paper 4, Variant 3
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Questions Discovered
130