12.1. Energy
A subsection of Biology, 9700, through 12. Energy and respiration
Listing 10 of 34 questions
Define the term respiratory quotient (RQ). summarises the respiration of an organic substance, A, in aerobic conditions. Complete in the spaces provided. C18H32O2 + O2 CO2 + 16H2O substance A Calculate the RQ for substance A. Write your answer to two decimal places. RQ = Use your calculated RQ value to suggest the group of compounds to which substance A belongs. Dinitrophenol (DNP) is a compound used in the production of a number of products, including chemical dyes, insecticides and wood preservers. People who work in factories with DNP are at risk of exposure if they do not follow health and safety guidelines. DNP is a molecule that can transport protons across the inner mitochondrial membrane, allowing protons to leak out of the intermembrane space. Suggest and explain the effects of DNP on aerobic respiration in human cells. Suggest two symptoms that may be experienced by people after exposure to DNP for several months.
9700_s20_qp_42
THEORY
2020
Paper 4, Variant 2
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During respiration, respiratory substrates such as glucose are used as a source of energy to produce ATP molecules. Cells can maintain a different concentration of ions within the cell compared with the extracellular environment. It is estimated that animals may use 50% of ATP made from respiration to maintain higher concentrations of some ions inside cells. Name the mechanism that can maintain a higher concentration of ions inside a cell. Only a proportion of energy released by the respiration of glucose is used to make ATP. • The energy yield from the respiration of glucose in aerobic conditions is 2870 kJ mol–1. • When ATP is hydrolysed to ADP, it releases 30.5 kJ mol–1 of energy. • It is estimated that 31 moles of ATP are made per mole of glucose respired. Calculate the percentage efficiency of glucose respiration. Show your working. % The energy that is not converted to ATP during respiration is released as heat energy. State one homeostatic use of this heat energy in mammals. State the term used to describe the reaction that results in the production of ATP during the Krebs cycle. When a person exercises, power is generated. Power is measured in joules per second (J s–1). The power generated when a person exercises will vary depending on the type and intensity of exercise. More power is generated when the intensity of exercise increases. An experiment was carried out to determine whether increasing the intensity of exercise in a healthy human male caused a change in the value of the respiratory quotient (RQ). • The man had a balanced diet. • The RQ was calculated at rest. • He carried out exercise for the same length of time on four separate days. • The intensity of exercise was increased over the four days, generating different powers. • The RQ was calculated for the four different powers generated. The results are shown in . at rest power generated / J s–1 RQ 0.2 0.4 0.6 0.8 1.0 1.2 With reference to , suggest what can be deduced from: the RQ at rest the RQ when the power generated is 110 J s–1 the RQ when the power generated is 200 J s–1. Explain why a person continues to breathe deeply and at a higher rate for some time after the person has stopped exercising.
9700_s21_qp_43
THEORY
2021
Paper 4, Variant 3
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The Santa Cruz tarplant, Holocarpha macradenia, is a tall annual plant that grows only in the coastal grasslands in California. An annual plant is one that grows, flowers, produces seeds and dies in less than one year. The tarplant used to be widely spread in California, but there are now only nine natural populations. It is listed as an endangered species. Suggest two reasons why the tarplant has become endangered. State three reasons why it is important to conserve species. 1. 2. 3. Tarplant seeds can survive in the soil for several years. Dormant seeds can be encouraged to germinate by scraping the soil, which exposes them to light. This stimulates the production of gibberellin in these seeds, which brings about germination. Explain how gibberellin brings about germination in seeds. The long-term survival of tarplant seeds in the soil provides a store of seeds that can help to ensure the future survival of the tarplant. Little is known about the survival of tarplant seeds in the soil, or what percentage of these seeds is able to germinate. Researchers therefore used computer models to predict how these factors could affect the likelihood that the tarplant might become extinct. In their models they used: • high or low survival values of tarplant seeds in the soil • different germination percentages of tarplant seeds. The predictions of the models are shown in . percentage germination of tarplant seeds risk of extinction / arbitrary units low survival value of seeds in soil high survival value of seeds in soil With reference to , describe the effect of each of the following on the risk of extinction of the tarplant: high compared to low survival of the tarplant seeds different germination percentages of the tarplant seeds. With reference to , discuss whether scraping the soil should be recommended as part of the management strategy to attempt to conserve the tarplant.
9700_s15_qp_41
THEORY
2015
Paper 4, Variant 1
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The Santa Cruz tarplant, Holocarpha macradenia, is a tall annual plant that grows only in the coastal grasslands in California. An annual plant is one that grows, flowers, produces seeds and dies in less than one year. The tarplant used to be widely spread in California, but there are now only nine natural populations. It is listed as an endangered species. Suggest two reasons why the tarplant has become endangered. State three reasons why it is important to conserve species. 1. 2. 3. Tarplant seeds can survive in the soil for several years. Dormant seeds can be encouraged to germinate by scraping the soil, which exposes them to light. This stimulates the production of gibberellin in these seeds, which brings about germination. Explain how gibberellin brings about germination in seeds. The long-term survival of tarplant seeds in the soil provides a store of seeds that can help to ensure the future survival of the tarplant. Little is known about the survival of tarplant seeds in the soil, or what percentage of these seeds is able to germinate. Researchers therefore used computer models to predict how these factors could affect the likelihood that the tarplant might become extinct. In their models they used: • high or low survival values of tarplant seeds in the soil • different germination percentages of tarplant seeds. The predictions of the models are shown in . percentage germination of tarplant seeds risk of extinction / arbitrary units low survival value of seeds in soil high survival value of seeds in soil With reference to , describe the effect of each of the following on the risk of extinction of the tarplant: high compared to low survival of the tarplant seeds different germination percentages of the tarplant seeds. With reference to , discuss whether scraping the soil should be recommended as part of the management strategy to attempt to conserve the tarplant.
9700_s15_qp_43
THEORY
2015
Paper 4, Variant 3
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Questions Discovered
34