12. Energy and respiration
A section of Biology, 9700
Listing 10 of 192 questions
Rice, Oryza sativa, is a staple food in many parts of the world. Rice is often grown in fields that are flooded with water for part of the growing season. The roots of young rice plants are highly tolerant of ethanol. Explain how this helps them to survive when the fields are flooded. Rice grains have a similar structure to those of maize. The endosperm makes up most of the rice grain. The endosperm is surrounded by an aleurone layer, which contains hydrolytic enzymes. Outside the aleurone layer is the fused pericarp and testa, containing large amounts of cellulose. Describe the function of the endosperm. Brown rice includes the pericarp and testa, whereas in white rice these have been removed during milling, along with most of the aleurone layer. Table 5.1 shows the nutrient content of samples of white and brown rice. Table 5.1 nutrient content per 100 g white rice brown rice lipid / g 0.8 2.4 dietary fibre / g 0.6 2.8 calcium / mg vitamin B1 / mg 0.07 0.26 protein / g 6.0 7.4 carbohydrate / g 82.0 77.7 With reference to the structure of rice grains, suggest why brown rice contains more protein than white rice. Explain why brown rice contains less carbohydrate per gram than white rice. Explain why the grains of cereals such as rice are staple foods in many parts of the world.
9700_w10_qp_41
THEORY
2010
Paper 4, Variant 1
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Rice, Oryza sativa, is a staple food in many parts of the world. Rice is often grown in fields that are flooded with water for part of the growing season. The roots of young rice plants are highly tolerant of ethanol. Explain how this helps them to survive when the fields are flooded. Rice grains have a similar structure to those of maize. The endosperm makes up most of the rice grain. The endosperm is surrounded by an aleurone layer, which contains hydrolytic enzymes. Outside the aleurone layer is the fused pericarp and testa, containing large amounts of cellulose. Describe the function of the endosperm. Brown rice includes the pericarp and testa, whereas in white rice these have been removed during milling, along with most of the aleurone layer. Table 5.1 shows the nutrient content of samples of white and brown rice. Table 5.1 nutrient content per 100 g white rice brown rice lipid / g 0.8 2.4 dietary fibre / g 0.6 2.8 calcium / mg vitamin B1 / mg 0.07 0.26 protein / g 6.0 7.4 carbohydrate / g 82.0 77.7 With reference to the structure of rice grains, suggest why brown rice contains more protein than white rice. Explain why brown rice contains less carbohydrate per gram than white rice. Explain why the grains of cereals such as rice are staple foods in many parts of the world.
9700_w10_qp_42
THEORY
2010
Paper 4, Variant 2
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Cultivated rice, Oryza sativa, is often grown in fields flooded with water. Explain how rice plants are adapted for growth with the roots submerged in water. Some varieties of cultivated rice are able to grow long internodes when they are submerged in water, keeping the leaves and flowers above water level (an internode is a length of stem between leaves). These varieties are known as deepwater rice. The snorkel genes SK1 and SK2, thought to be responsible for this response, were identified in a variety of deepwater rice, C9285. A non-deepwater variety, T65, did not have these genes. When submerged, rice plants produce the gaseous plant hormone ethene. This has a very low solubility in water, so it accumulates in the aerenchyma tissue in the rice stems. shows the concentration of ethene in the aerenchyma of T65 and C9285 when the plants are submerged in water for 18 hours. time after submergence / h production of ethene / arbitrary units C9285 T65 shows the results of exposing T65 and C9285 to different concentrations of ethene in dry conditions. T65 T65 T65 C9285 C9285 C9285 no ethene 10 ppm ethene 100 ppm ethene mean internode elongation / cm With reference to , describe the effect of submergence in water on the production of ethene in rice. With reference to , compare the effect of ethene on internode elongation in C9285 and T65. The snorkel genes were found to be expressed when the plant was exposed to ethene. The expression of these genes results in increased production of gibberellin, GA. shows the effect of submergence on GA production in C9285 and in T65. time after submergence / h C9285 T65 GA produced / arbitrary units With reference to , and your knowledge of the functions of GA, suggest an explanation for the differences in the effects of ethene in C9285 and T65 shown in . Cultivated rice has been developed from the wild rice species Oryza rufipogon and Oryza nivara. O. rufipogon has a strong deepwater elongation response, but O. nivara has only a slight elongation response. Another species, Oryza glumaepatula, shows a strong elongation response. • O. rufipogon has both the snorkel genes, SK1 and SK2. • O. nivara has SK1, but an addition mutation has produced a stop triplet within SK2. • O. glumaepatula has SK2, but not SK1. Describe what this information indicates about the relative importance of the genes SK1 and SK2 in the deepwater elongation response. Explain how an addition mutation could produce a stop triplet. Deepwater rice is the main food crop in many parts of the world that undergo flooding in the rainy season. Many varieties of deepwater rice have lower yields than non-deepwater varieties. Suggest how a deepwater rice variety with high yield could be produced, using artificial selection.
9700_w11_qp_41
THEORY
2011
Paper 4, Variant 1
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Cultivated rice, Oryza sativa, is often grown in fields flooded with water. Explain how rice plants are adapted for growth with the roots submerged in water. Some varieties of cultivated rice are able to grow long internodes when they are submerged in water, keeping the leaves and flowers above water level (an internode is a length of stem between leaves). These varieties are known as deepwater rice. The snorkel genes SK1 and SK2, thought to be responsible for this response, were identified in a variety of deepwater rice, C9285. A non-deepwater variety, T65, did not have these genes. When submerged, rice plants produce the gaseous plant hormone ethene. This has a very low solubility in water, so it accumulates in the aerenchyma tissue in the rice stems. shows the concentration of ethene in the aerenchyma of T65 and C9285 when the plants are submerged in water for 18 hours. time after submergence / h production of ethene / arbitrary units C9285 T65 shows the results of exposing T65 and C9285 to different concentrations of ethene in dry conditions. T65 T65 T65 C9285 C9285 C9285 no ethene 10 ppm ethene 100 ppm ethene mean internode elongation / cm With reference to , describe the effect of submergence in water on the production of ethene in rice. With reference to , compare the effect of ethene on internode elongation in C9285 and T65. The snorkel genes were found to be expressed when the plant was exposed to ethene. The expression of these genes results in increased production of gibberellin, GA. shows the effect of submergence on GA production in C9285 and in T65. time after submergence / h C9285 T65 GA produced / arbitrary units With reference to , and your knowledge of the functions of GA, suggest an explanation for the differences in the effects of ethene in C9285 and T65 shown in . Cultivated rice has been developed from the wild rice species Oryza rufipogon and Oryza nivara. O. rufipogon has a strong deepwater elongation response, but O. nivara has only a slight elongation response. Another species, Oryza glumaepatula, shows a strong elongation response. • O. rufipogon has both the snorkel genes, SK1 and SK2. • O. nivara has SK1, but an addition mutation has produced a stop triplet within SK2. • O. glumaepatula has SK2, but not SK1. Describe what this information indicates about the relative importance of the genes SK1 and SK2 in the deepwater elongation response. Explain how an addition mutation could produce a stop triplet. Deepwater rice is the main food crop in many parts of the world that undergo flooding in the rainy season. Many varieties of deepwater rice have lower yields than non-deepwater varieties. Suggest how a deepwater rice variety with high yield could be produced, using artificial selection.
9700_w11_qp_42
THEORY
2011
Paper 4, Variant 2
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Vitamin A deficiency is a major health problem in parts of the world where children have a limited diet. Rice enhanced with pro-vitamin A has been produced through genetic engineering. This new rice, called Golden Rice, contains large amounts of β-carotene, which is used in the human body to synthesise vitamin A. From this Golden Rice, newer varieties of Golden Rice have been developed by selective breeding. shows how Golden Rice was originally produced by genetic engineering. step 1 enzymes were used to obtain genes coding for β-carotene from both maize and the bacterium, Pantoea ananatis step 2 plasmids were cut open by enzymes step 3 the genes coding for β-carotene were introduced into the plasmids, together with promoters step 4 these recombinant plasmids were introduced into the bacterium, Agrobacterium tumefaciens step 5 A. tumefaciens was used to deliver the recombinant plasmids into rice plant embryos step 6 these embryos were grown on to produce Golden Rice plants Name the types of enzyme used in step 1 and step 2. Name the enzyme used in step 3. Explain why promoters were introduced along with the genes for β-carotene in step 3. Describe the properties of plasmids that make them suitable for their roles in the production of Golden Rice. Rice is an important food crop in many different countries. Farmers in different parts of the world have developed rice varieties that grow well in the local climate and soil conditions. Selective breeding programmes have been carried out in which Golden Rice was interbred with local rice varieties to produce varieties of Golden Rice that grow well in different localities. Explain why the original Golden Rice had to be developed by genetic engineering, but locally-adapted varieties of Golden Rice could be developed by selective breeding. An investigation was carried out to check that β-carotene from Golden Rice can be converted to vitamin A in the body. Golden Rice plants were grown using water whose molecules contained deuterium instead of ordinary hydrogen. Deuterium is an isotope of hydrogen that contains a neutron as well as a proton in its nucleus. The β-carotene synthesised in these rice plants contained deuterium. Volunteers ate a measured dose of rice taken from these Golden Rice plants. The concentrations in the blood of vitamin A containing deuterium were measured on the day before they ate the rice, and then over the next 6 days. shows the results. concentration of vitamin A containing deuterium / arbitrary units Golden Rice eaten time / days Explain why the Golden Rice was grown using water containing deuterium. Suggest why it took several hours after the Golden Rice had been eaten for the maximum concentration of vitamin A containing deuterium to be reached.
9700_w16_qp_43
THEORY
2016
Paper 4, Variant 3
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When gold is associated with mineral ores such as iron sulfide, the sulfides must be oxidised to release the gold particles. Since the mid 1990s, gold has been extracted from such ores by bioleaching. Suitable bacteria oxidise iron sulfide to soluble iron sulfate, releasing Fe3+ and SO4 2– ions. The reaction releases heat energy and temperatures within a heap of ore that is being bioleached (a bioheap) can reach 70 °C or higher. Examples of bacteria used in this bioleaching are shown in Table 2.1. Table 2.1 example of bacterium temperature range for growth / °C activity natural habitat Acidithiobacillus ferrooxidans 35 – 45 oxidise iron and sulfur compounds acid springs Sulfobacillus thermosulfidooxidans 45 – 65 Sulfolobus metallicus 65 – 95 With reference to Table 2.1, suggest a natural habitat for organisms such as S. thermosulfidooxidans and S. metallicus why all three species of bacteria, rather than just one species, are mixed with ore in a bioheap. The rate of oxidation of the iron in iron sulfide ore was compared in the presence and absence of A. ferrooxidans at pH 2.0. The results are shown in . in presence of A. ferrooxidans in absence of A. ferrooxidans 2.0 concentration of Fe3+ ions / arbitrary units 1.0 1.5 0.5 time / days With reference to , describe the effect of A. ferrooxidans on the oxidation of the ore. Explain why bioleaching is now used on a large scale throughout the world. Gold-bearing sulfide ores often contain arsenic, which is potentially toxic to the bacteria used in bioleaching. However, arsenic-resistant strains of A. ferrooxidans have been found in some mines. The activity of two strains of the bacterium, in the presence and absence of arsenic ions, is shown in Table 2.2. Table 2.2 oxidation rate of iron in the ore / mg dm–3 h–1 strain of A. ferrooxidans arsenic ions absent arsenic ions present Describe the results shown in Table 2.2 and explain the role of natural selection in the evolution of arsenic-resistant bacteria.
9700_s11_qp_41
THEORY
2011
Paper 4, Variant 1
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DCPIP is an indicator and can be used to determine the rate of respiration of organisms such as yeast. State the category of indicators to which DCPIP belongs. Describe the colour change that occurs in DCPIP during experiments to determine the rate of respiration. An investigation was carried out to determine the effect of temperature on the rate of respiration of yeast. • A suspension of yeast cells was added to a test‑tube containing glucose solution. • A further four test‑tubes were set up in the same way. • One test‑tube was placed in a water‑bath at 10 °C for 5 minutes. • DCPIP was added to the test‑tube and the time taken for the DCPIP to change colour was measured. • The experiment was repeated using the other test‑tubes at 20 °C, 30 °C, 40 °C and 50 °C. The results are shown in . temperature / °C time taken for DCPIP to change colour / minutes State two variables that need to be kept constant in this experiment. Explain the results shown in .
9700_w24_qp_42
THEORY
2024
Paper 4, Variant 2
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Questions Discovered
192