12. Energy and respiration
A section of Biology, 9700
Listing 10 of 192 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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is a diagram of part of a mitochondrion showing some of the events occurring in oxidative phosphorylation. matrix reduced NAD NAD inner membrane H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ e– outer membrane Key = carrier = movement of e– intermembrane space e– e– = movement of H+ e– e– Z Y water State two sources of the reduced NAD in . With reference to , outline the role of carriers in the inner membrane. With reference to , name Y and Z. Y Z Explain why it is an advantage to the cell for the inner membrane of the mitochondrion to be folded.
9700_s18_qp_43
THEORY
2018
Paper 4, Variant 3
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Maize, Zea mays, is a cereal crop that is adapted for growth at high temperatures. However, it does not cope with drought as well as some other crops, such as sorghum. An investigation was carried out into the effect of low water availability on the activity of mitochondria taken from maize seedlings. Young seedlings were uprooted and left in dry air for varying periods of time to reduce the water potential of their tissues. Explain why this treatment reduced the water potential of the maize seedling tissues. After drying in air, mitochondria were extracted from the tissues of the seedlings. The extracted mitochondria were provided with succinate, which is one of the intermediate compounds in the Krebs cycle, and also with ADP and inorganic phosphate. The rate at which the extracted mitochondria took up oxygen was measured. The results are shown in . –30 –25 –20 –15 –10 –5 +5 +10 rate of oxygen uptake by extracted mitochondria / arbitrary units water potential of the tissues from which the mitochondria were extracted / kPa Describe the results shown in . The mitochondria take up oxygen. Explain how this oxygen, plus the succinate, ADP and inorganic phosphate, are used by the mitochondria. In a further experiment, it was found that mitochondrial membranes lost their normal structure when the water potential was low. Suggest why membranes in cells lose their normal structure when the water potential is low. Suggest how this could explain the results shown in . In tissues where water potential is low, the mitochondria of sorghum are affected in a very similar way to those of maize. Describe two ways in which sorghum plants are adapted to prevent the development of low water potentials in their tissues during drought conditions. 1. 2.
9700_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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Questions Discovered
192