12.2. Respiration
A subsection of Biology, 9700, through 12. Energy and respiration
Listing 10 of 158 questions
The filamentous fungus, Fusarium venenatum, can be grown in a fermenter and harvested as mycoprotein. It is sold as a food in a number of different countries. The fungus is grown in continuous culture in 150 000 dm3 airlift fermenters, in which the introduction of bubbles of compressed air both oxygenates and stirs the contents. The fungus grows as narrow, branched filaments, giving the harvested mycoprotein a naturally chewy, fibrous texture. Approximately 300 kg of fungus can be harvested per hour. Explain what is meant by the term continuous culture. After about six weeks, mutants may appear in the fungal population, for example, a more highly-branched form of the fungus. The fermenter is emptied, cleaned and repopulated with the original strain of F. venenatum every six weeks. Explain why the fermentation process should be stopped before mutants appear. Approximately 12% of the harvested fungus is protein. Calculate the approximate mass of protein harvested in one day during continuous culture. Show your working. answer
9700_s13_qp_43
THEORY
2013
Paper 4, Variant 3
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A group of membrane proteins which transport sugars out of cells have been identified and called SWEETs. They are found in the cell surface membranes of both animal and plant cells, including mammalian liver cells and rice mesophyll cells. Each SWEET is a protein with seven coiled regions which together make a pore through a membrane bilayer as shown in . coiled region Explain why, to enter or leave a cell, sugars need molecules such as SWEETS. Suggest how a SWEET is held within the membrane bilayer. The bacterium, Xanthomonas oryzae (Xoo), causes the disease known as bacterial leaf blight in rice plants. It infects the intercellular spaces of the leaves of the host plant. Then, by switching on SWEET genes in the mesophyll cells, it stimulates the secretion of glucose into the intercellular spaces. Several different recessive alleles have been found, in rice plants from different countries, which give resistance to bacterial leaf blight. All these alleles have a mutation in the promoter of the SWEET gene. The effect of Xoo on wild type and resistant rice plants is compared in . wild type rice Xoo secretes a chemical into the rice mesophyll cells chemical binds with promoter region of SWEET gene SWEET protein produced and inserted into cell surface membrane switches on SWEET gene glucose secreted into intercellular spaces Xoo multiplies resistant rice Xoo secretes a chemical into the rice mesophyll cells chemical cannot bind with mutated promoter region of SWEET gene number of Xoo cells remains low Using the information in , explain this resistance of rice plants to Xoo. Explain why it would be difficult to transfer this resistance into susceptible rice plants by genetic engineering. Explain why the presence of large numbers of Xoo in the intercellular air spaces of rice plants affects the ability of the plants to grow with their roots submerged in water.
9700_s14_qp_42
THEORY
2014
Paper 4, Variant 2
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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_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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Questions Discovered
158