AQA GCSE · Combined Science: Trilogy 8464
1 multiple-choice questions marked as you go, and 5 written questions with worked solutions. All on Bioenergetics.
(HT only) A student uses the inverse square law to investigate the effect of light intensity on the rate of photosynthesis. If the student moves a light source from a distance of \( 10 \text{ cm} \) to \( 30 \text{ cm} \) from the plant, what is the resulting change in light intensity?
Explain why a person's breathing rate and heart rate remain high for a period of time after they have finished vigorous exercise.
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A scientist measures the rate of anaerobic respiration in yeast cells. Explain why the net energy transfer to the environment is significantly lower per molecule of glucose in anaerobic respiration compared to aerobic respiration.
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Explain how the liver and the circulatory system work together to remove the build-up of lactic acid after a period of anaerobic respiration in human muscle cells.
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A student carries out an experiment to investigate the rate of aerobic respiration in germinating seeds by measuring oxygen consumption. They use a simple respirometer containing soda lime to absorb carbon dioxide produced by the seeds.
(a) Explain why soda lime is essential in this experiment to ensure the change in gas volume accurately reflects the rate of respiration. (2)
(b) During the experiment, the seeds consume \( 0.45 \text{ cm}^3 \) of oxygen every \( 5 \text{ minutes} \). Calculate the rate of respiration in \( \text{cm}^3/\text{hour} \). Show your working. (2)
(c) Germinating seeds can also respire anaerobically if oxygen is limited. Identify the product of anaerobic respiration in germinating plant cells and explain why this process transfers significantly less energy than aerobic respiration. (2)
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Photosynthesis and respiration are essential reactions for life. While photosynthesis is endothermic, aerobic respiration is exothermic.
(a) Write the balanced chemical equation for aerobic respiration using chemical symbols. (2)
(b) (HT only) During vigorous exercise, the body may switch to anaerobic respiration. Explain why this leads to an oxygen debt and describe how the body eventually removes the lactic acid produced during this process. (4)
(c) Metabolism is the sum of all reactions in a cell. Identify two specific metabolic processes that involve the synthesis of new molecules from the products of digestion. (2)
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