19.3. Nutrient cycles
A subsection of Biology, 0610, through 19. Organisms and their environment
Listing 10 of 114 questions
For Examiner's Use Nitrogen gas makes up about 80 % of the Earth’s atmosphere. Only those organisms that are able to fix nitrogen can use it. All other organisms rely on the recycling of nitrogen from nitrogen-containing compounds, such as proteins and DNA. shows the nitrogen cycle on a small farm in Ghana. nitrogen (N2) in atmosphere ammonium ions (NH4 +) in bacteria in root nodules of legumes amino acids in bacteria in root nodules of legumes amino acids in legumes protein in legumes protein in goat urea in blood of goat amino acids in intestine of goat nitrate ions (NO3 –) in soil ammonium ions (NH4 +) in soil urea in urine of goat protein in faeces of goat Q P R S Q T U Complete Table 6.1 by identifying the processes, P to U, in the nitrogen cycle shown in . One process, S, has been completed for you. Table 6.1 stage process P Q R S deamination T U For Examiner's Use It is difficult to improve legume crops by traditional plant breeding methods. Scientists in Ghana have used a different approach. They exposed seeds of two varieties of winged bean, Psophocarpus tetragonolobus, to ionising radiation. Seeds that had been exposed to radiation (irradiated seeds) and seeds that had not been irradiated were grown under identical conditions. After 45 days, the numbers of root nodules on the plants that grew from these seeds were recorded. The dry mass of the root nodules on each plant was also determined and recorded. The results of the investigation are shown in Table 6.2. Table 6.2 variety 1 variety 2 feature non-irradiated irradiated non-irradiated irradiated mean number of nodules per plant at 45 days mean dry mass of nodules per plant at 45 days / g 0.09 0.21 0.14 0.24 Use the results in Table 6.2 to describe the effect of radiation on the plants in both varieties. For Examiner's Use Suggest and explain what happens to the seeds when they are exposed to ionising radiation. Researchers use plants that show useful features in selective breeding to improve varieties of the winged bean. The improvement of winged beans by selective breeding is an example of artificial selection. Suggest how selective breeding is carried out with plants. Scientists in Australia have put a gene from the bacterium Bacillus thuringiensis (Bt) into the cowpea, an important crop in Africa. This gene gives resistance against the cowpea pod borer, an insect pest that reduces the yield of cowpeas. Explain how the method used by the Australian scientists differs from the technique used by the Ghanaian scientists. For Examiner's Use Legumes, such as cowpeas and winged beans, are grown in between maize plants in a method known as intercropping. Suggest the advantages to farmers of growing legumes and maize together in the same field at the same time.
0610_s12_qp_32
THEORY
2012
Paper 3, Variant 2
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For Examiner's Use List four chemical elements that are found in proteins. 1. 2. 3. 4. is a photograph of some root nodules from a pea plant, which is a type of legume. Nodules like those in develop on the roots of pea plants and other legumes when the soil is lacking in nitrate ions. Explain what happens inside the nodule to help legume plants grow in soils lacking nitrate ions. For Examiner's Use After the peas have been harvested, the plants are ploughed back into the soil. Describe what happens in the soil to convert dead plant material into nitrate ions that plants can absorb. Nutrients in the soil can act as a limiting factor for crop growth. List three other factors that may limit the growth of a crop plant. 1. 2. 3. QUESTION 6 CONTINUES ON PAGE 18 For Examiner's Use The soya bean aphid is an insect pest of soya bean plants in North America. The aphids can show an exponential growth rate where populations can double in two to three days under favourable conditions. shows the growth of soya bean aphids in a field in North America during the growing season. time / days number of aphids per plant Suggest why the population of aphids did not increase rapidly until about day 40.
0610_w09_qp_31
THEORY
2009
Paper 3, Variant 1
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For Examiner's Use List four chemical elements that are found in proteins. 1. 2. 3. 4. is a photograph of some root nodules from a pea plant, which is a type of legume. Nodules like those in develop on the roots of pea plants and other legumes when the soil is lacking in nitrate ions. Explain what happens inside the nodule to help legume plants grow in soils lacking nitrate ions. For Examiner's Use After the peas have been harvested, the plants are ploughed back into the soil. Describe what happens in the soil to convert dead plant material into nitrate ions that plants can absorb. Nutrients in the soil can act as a limiting factor for crop growth. List three other factors that may limit the growth of a crop plant. 1. 2. 3. QUESTION 6 CONTINUES ON PAGE 18 For Examiner's Use The soya bean aphid is an insect pest of soya bean plants in North America. The aphids can show an exponential growth rate where populations can double in two to three days under favourable conditions. shows the growth of soya bean aphids in a field in North America during the growing season. time / days number of aphids per plant Suggest why the population of aphids did not increase rapidly until about day 40.
0610_w09_qp_32
THEORY
2009
Paper 3, Variant 2
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For Examiner's Use Nitrogen is one of the most important chemical elements in the biosphere. Nitrogen must be continually recycled if life is to continue on Earth. Savanna grasslands are an important ecosystem in Africa. shows part of the nitrogen cycle in a grassland ecosystem in southern Africa. nitrogen gas (N2) in the atmosphere nitrate ions in the soil ammonia in the soil urea in urine cheetah D E F lightning C impala D B A nitrogen fixation Cassia mimosoides legume that fixes nitrogen Name: a type of nitrogen-containing compound that is made by Cassia mimosoides, eaten by the impala and by the cheetah; the type of consumer as represented by the cheetah; For Examiner's Use the process by which urea is removed from the body of the animals as shown by D; process F. Explain the importance of recycling nitrogen in ecosystems, such as the African savanna. The most common plants that grow in the African savanna are grasses. There are very few legume plants, such as C. mimosoides. Suggest reasons why C. mimosoides is a rare plant in the African savanna. For Examiner's Use Explain why there are far fewer cheetah than impala. The cheetah is an endangered species. It is important to conserve their food supply and all the species that inhabit their ecosystem. Explain why.
0610_w13_qp_31
THEORY
2013
Paper 3, Variant 1
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Questions Discovered
114