12.2. Respiration
A subsection of Biology, 9700, through 12. Energy and respiration
Listing 10 of 158 questions
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
158