12. Energy and respiration
A section of Biology, 9700
Listing 10 of 192 questions
During aerobic respiration, cells respire substrates such as glucose to produce ATP. Some events that occur during aerobic respiration are: • The respiratory substrate breaks down into smaller and smaller molecules. These series of reactions are described as catabolism. • Coenzymes take part in various reactions. In some reactions, coenzymes are reduced or oxidised. • Carbon dioxide is released. Aerobic respiration occurs in four successive stages: glycolysis (G), link reaction (LR), Krebs cycle (KC) and oxidative phosphorylation (OP). Complete Table 3.1 to show which events occur in each stage of aerobic respiration. Use a tick (✓) to show that the event does occur or a cross (✗) to show that the event does not occur. Table 3.1 event stage G LR KC OP catabolism coenzyme is reduced or oxidised a coenzyme forms a covalent bond with a respiratory intermediate carbon dioxide is released A new hand‑held technological device shows the main type of respiratory substrate being used in the cells of a person. The device consists of a carbon dioxide sensor and air‑flow meter. The person inhales through the device for a fixed time and then exhales into it. The device calculates the respiratory quotient (RQ) value to show whether the cells are mainly respiring carbohydrates or lipids. Explain how the device calculates the RQ value and how this shows whether the cells are mainly respiring carbohydrates or lipids. … … … … … … State the difference in the relative energy values of carbohydrates and lipids as respiratory substrates, and explain the reasons for the difference. … … … … … …
9700_w24_qp_41
THEORY
2024
Paper 4, Variant 1
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During aerobic respiration, cells respire substrates such as glucose to produce ATP. Some events that occur during aerobic respiration are: • The respiratory substrate breaks down into smaller and smaller molecules. These series of reactions are described as catabolism. • Coenzymes take part in various reactions. In some reactions, coenzymes are reduced or oxidised. • Carbon dioxide is released. Aerobic respiration occurs in four successive stages: glycolysis (G), link reaction (LR), Krebs cycle (KC) and oxidative phosphorylation (OP). Complete Table 3.1 to show which events occur in each stage of aerobic respiration. Use a tick (✓) to show that the event does occur or a cross (✗) to show that the event does not occur. Table 3.1 event stage G LR KC OP catabolism coenzyme is reduced or oxidised a coenzyme forms a covalent bond with a respiratory intermediate carbon dioxide is released A new hand‑held technological device shows the main type of respiratory substrate being used in the cells of a person. The device consists of a carbon dioxide sensor and air‑flow meter. The person inhales through the device for a fixed time and then exhales into it. The device calculates the respiratory quotient (RQ) value to show whether the cells are mainly respiring carbohydrates or lipids. Explain how the device calculates the RQ value and how this shows whether the cells are mainly respiring carbohydrates or lipids. … … … … … … State the difference in the relative energy values of carbohydrates and lipids as respiratory substrates, and explain the reasons for the difference. … … … … … …
9700_w24_qp_43
THEORY
2024
Paper 4, Variant 3
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shows a transmission electron micrograph of a section through a mitochondrion. P Q Table 6.1 shows some structures and compounds involved in aerobic respiration. Use letter P or letter Q from to complete Table 6.1 to show the location of the structures and where the compounds are used. Table 6.1 compound or structure location ATP synthase acetyl CoA phospholipid bilayer oxaloacetate The number of mitochondria differs from cell to cell. Cells also vary in size and volume. Table 6.2 shows the mean number of mitochondria per cell, the mean cell volume and the mean number of mitochondria per µm3 of three types of mammalian cells. Table 6.2 cell type mean number of mitochondria per cell mean cell volume / µm3 mean number of mitochondria per µm3 fat cell 600 000 0.17 # 10-3 heart cell 45 000 44.44 # 10-3 liver cell 125 000 Calculate the mean number of mitochondria per µm3 for the liver cell. Write your answer in Table 6.2. Suggest reasons for the difference in mean number of mitochondria per µm3 between the fat cell and the heart cell. Suggest why it is difficult to compare the ability of the three types of cell to respire aerobically, based only on the mean number of mitochondria per cell.
9700_s18_qp_41
THEORY
2018
Paper 4, Variant 1
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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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outlines some steps in glucose metabolism in mammalian cells. glucose reduced NAD NAD lactate oxygen not available glucose glycogen oxygen available oxygen available NAD ADP ATP pyruvate With reference to : name the part of the cell where glucose is converted to pyruvate explain why, in the absence of oxygen, pyruvate needs to be converted to lactate name the enzyme responsible for the conversion of pyruvate to lactate name the type of reaction and the type of bonds formed when glucose molecules are used to make glycogen. reaction bonds Describe how anaerobic respiration in yeast cells differs from anaerobic respiration in mammalian cells. The respiratory quotient (RQ) is used to determine the type of respiratory substrate, such as carbohydrate or lipid, which an organism uses at any one time. State how the RQ is calculated. State the typical RQ values obtained from the respiration of carbohydrates and lipids. carbohydrate lipid Suggest what would happen to the RQ value when respiration becomes anaerobic.
9700_w12_qp_43
THEORY
2012
Paper 4, Variant 3
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A respirometer is a piece of apparatus that can be used to measure the rate of respiration of living tissue such as germinating peas. A simple respirometer is shown in . cm U-shaped tube ruler coloured liquid syringe wire gauze germinating peas test-tube potassium hydroxide solution A student carried out an investigation to determine the effect of temperature on the rate of respiration of germinating peas. • The student set up the respirometer as shown in and placed the respirometer in a water-bath at 10 °C. • After five minutes, the student used the syringe to adjust the position of the coloured liquid in the right-hand side of the U-shaped tube so that it lined up with 0 cm on the ruler. The student immediately started a timer. • The germinating peas used up oxygen, causing the coloured liquid in the U-shaped tube to move. • The student measured the distance moved by the coloured liquid after 20 minutes. • The student repeated the experiment at temperatures of 20 °C, 30 °C, 40 °C and 50 °C. State the function of the potassium hydroxide solution used in the investigation. Suggest how the validity of the results could be assessed. Explain why the respirometer was left in the water-bath for five minutes before starting the experiment. The rate of movement of the coloured liquid in the U-shaped tube, calculated from the results, is shown in Table 6.1. Table 6.1 temperature / °C rate of movement / mm min–1 0.40 0.70 1.30 1.15 0.60 Plot a graph of the results shown in Table 6.1 on the grid in . Draw a curved line of best fit. 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 rate of movement / mm min–1 temperature / °C The rate of movement of the coloured liquid is related to the rate of respiration. Explain the effect of temperature on the rate of respiration shown in Table 6.1 and .
9700_m24_qp_42
THEORY
2024
Paper 4, Variant 2
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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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Outline the process of glycolysis in a mammalian cell. Within a mammalian cell, ATP can be produced in a number of ways, including: • substrate level phosphorylation during the Krebs cycle • oxidative phosphorylation. Table 7.1 compares both processes. Complete Table 7.1. Use a tick () if the statement is correct or a cross () if the statement is incorrect. The first row has been done for you. Table 7.1 statement substrate level phosphorylation oxidative phosphorylation enzymes are involved   occurs in cytoplasm occurs in mitochondria channel proteins are involved An investigation into the RQ values of germinating maize seeds was carried out. • A sample of maize seeds was soaked in water for one hour. • The mean RQ value of some of the seeds was then calculated and the remaining seeds were then planted in soil. • After 12 hours, the mean RQ value of some of the planted seeds was calculated. • The remaining seeds were allowed to germinate and grow into seedlings. • After 21 days, the mean RQ value of some of the seedlings was calculated. Table 7.2 shows the results of the investigation. Table 7.2 stage of germination and growth mean RQ seeds soaked in water 5.6 seeds after 12 hours in the soil 0.8 seedlings after 21 days 1.0 Suggest an explanation for each of the RQ values shown in Table 7.2. seeds soaked in water seeds after 12 hours in the soil seedlings after 21 days
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
192