12.2. Respiration
A subsection of Biology, 9700, through 12. Energy and respiration
Listing 10 of 158 questions
The production of ATP by oxidative phosphorylation takes place in the electron transport chain in a mitochondrion. State the part of the mitochondrion in which the electron transport chain is found. Describe briefly where the electrons that are passed along the electron transport chain come from. Describe the role of oxygen in the process of oxidative phosphorylation. The brain depends on a constant supply of oxygen for aerobic respiration. Anaerobic respiration is not sufficient to keep neurones in the brain alive. This is because neurones require especially large amounts of ATP. Up to 80% of the ATP is used to provide energy for the Na+ / K+ pump. When a person suffers a stroke, blood flow to part of the brain is stopped, so some neurones receive no oxygen. ATP production by oxidative phosphorylation stops. shows some of the ways in which the lack of ATP affects a neurone in the brain. no ATP Na+ / K+ pump stops working membrane depolarises voltage-gated Ca2+ channels open Ca2+ ions flood into the neurone Ca2+ ions activate enzymes that eventually destroy the neurone Explain why the membrane of the neurone depolarises when the Na+ / K+ pump stops working. Suggest why calcium ions flood into the neurone when the Na+ / K+ pump stops working. The freshwater turtle, Trachemys scripta, is able to survive for long periods in conditions of very low oxygen concentration. As in humans, the rate of activity of the Na+ / K+ pump in the neurones in its brain falls sharply. However, in turtles this does not result in damage to these cells. A better understanding of how the neurones in the turtle’s brain survive in these conditions could lead to new treatments for people who have suffered a stroke. Experiments show that, in turtle brain neurones, in conditions of low oxygen availability: • most ion channels in the cell surface membranes immediately close • after about four hours, the quantity of mRNA involved in the synthesis of proteins used to build ion channels, falls to less than one fifth of normal concentrations. Suggest how the closure of ion channels in the neurones of the turtle in very low oxygen concentrations could allow the cells to survive. Suggest what causes the quantity of mRNA for protein channels to fall.
9700_s13_qp_42
THEORY
2013
Paper 4, Variant 2
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represents the link reaction. R + coenzyme A S + acetyl coenzyme A NAD reduced NAD With reference to : name substances R and S R S explain what happens to the reduced NAD. The pH of the blood of an athlete decreases during a race and returns to its normal level after the race. The decrease in the pH of the blood is caused by the presence of waste products that have been excreted by cells during respiration. Name the waste products that are excreted and describe what occurs to these products to help return the pH of the blood back to a normal level.
9700_s17_qp_42
THEORY
2017
Paper 4, Variant 2
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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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Questions Discovered
158