GCSE Biology Topic 4: Bioenergetics MCQs – 30 Practice Questions with Answers (AQA 8461)
Free practice for AQA GCSE Biology 8461 on photosynthesis, limiting factors, aerobic and anaerobic respiration, response to exercise and metabolism, with a short explanation after every question.
Photosynthesis
Q1. Which word equation summarises photosynthesis?
- (A) Glucose plus oxygen gives carbon dioxide plus water
- (B) Glucose gives lactic acid
- (C) Carbon dioxide plus water gives glucose plus oxygen
- (D) Glucose gives ethanol plus carbon dioxide
Show Answer
Answer: C – In photosynthesis a plant uses light energy to build glucose from carbon dioxide and water, releasing oxygen as a by-product.
Q2. Where in a plant cell does photosynthesis take place, and which pigment absorbs the light?
- (A) In the chloroplasts, using chlorophyll
- (B) In the mitochondria, using haemoglobin
- (C) In the nucleus, using melanin
- (D) In the vacuole, using cell sap
Show Answer
Answer: A – Chloroplasts contain chlorophyll, the green pigment that captures light energy for the photosynthetic reaction.
Q3. Photosynthesis is described as endothermic. What does this mean for energy in the reaction?
- (A) Energy is released to the surroundings as heat
- (B) No energy is involved at all
- (C) Energy is stored in carbon dioxide
- (D) Energy is transferred from the surroundings into the reaction by light
Show Answer
Answer: D – An endothermic reaction takes in energy from its surroundings, and photosynthesis takes in light energy to build glucose.
Q4. A plant makes glucose in its leaves. Which of these is a direct use of that glucose inside the plant?
- (A) It is broken down in respiration to transfer energy
- (B) It is turned into haemoglobin for blood in a typical living organism
- (C) It is excreted as urea in urine
- (D) It is used to make chlorophyll directly
Show Answer
Answer: A – Glucose made by photosynthesis can be used in respiration, converted to cellulose for cell walls, used to make amino acids, or stored as starch or oils and fats.
Q5. Why does a plant convert some of its glucose into starch for storage?
- (A) Starch dissolves easily and leaks from cells
- (B) Starch is soluble, so it can be transported quickly
- (C) Starch is a gas that escapes from leaves
- (D) Starch is insoluble, so it does not affect the water balance of storage cells
Show Answer
Answer: D – Converting glucose to insoluble starch lets the plant store energy without the stored material dissolving and disturbing osmosis in its cells.
Q6. A plant needs amino acids to build proteins. Which two raw materials does it combine to make amino acids?
- (A) Glucose and oxygen
- (B) Starch and carbon dioxide
- (C) Cellulose and water
- (D) Glucose and nitrate ions
Show Answer
Answer: D – Plants combine glucose from photosynthesis with nitrate ions absorbed from the soil to build amino acids, which are then assembled into proteins.
Limiting Factors and the Rate of Photosynthesis
Q7. What is meant by a limiting factor for photosynthesis?
- (A) The factor that is present in the largest amount under the conditions given
- (B) The factor that is in shortest supply and therefore holds back the rate
- (C) The factor that stops photosynthesis permanently
- (D) The factor that only affects respiration
Show Answer
Answer: B – When one factor, such as light, carbon dioxide or temperature, is in short supply, it limits the rate even if the other factors are plentiful.
Q8. A graph of photosynthesis rate against light intensity rises at first and then levels off. What does the flat part of the graph show?
- (A) Another factor has become limiting, so extra light cannot raise the rate further
- (B) Light is still the limiting factor
- (C) Photosynthesis has stopped completely
- (D) The plant has run out of chlorophyll permanently in this type of tissue over a short period of time
Show Answer
Answer: A – Once light is no longer in shortest supply, something else, such as carbon dioxide concentration or temperature, limits the rate and the graph plateaus.
Q9. Raising the temperature from 10 degrees to 25 degrees increases the rate of photosynthesis. What happens if the temperature keeps rising well beyond the optimum?
- (A) The rate keeps rising without limit
- (B) The rate stays the same at every temperature
- (C) The rate falls because enzymes involved in photosynthesis begin to denature
- (D) The plant starts respiring aerobically instead of photosynthesizing
Show Answer
Answer: C – Higher temperature speeds reactions up to an optimum, but beyond it the enzymes lose their shape and activity falls.
Q10. A greenhouse grower raises the carbon dioxide concentration around tomato plants. When will this increase the rate of photosynthesis?
- (A) Only when carbon dioxide is the limiting factor
- (B) At all times, regardless of light and temperature
- (C) Only at night, when no light is available
- (D) Only when the plants have no chlorophyll
Show Answer
Answer: A – Extra carbon dioxide helps only while carbon dioxide is in shortest supply; if light or temperature limits the rate instead, adding more gas makes no difference.
Q11. A leaf with very little chlorophyll photosynthesises slowly even in bright light. Why?
- (A) Less carbon dioxide can enter through the stomata at ordinary temperatures
- (B) Less water reaches the leaf through the xylem
- (C) Less light energy is absorbed, so the reaction is held back
- (D) Less oxygen is released by respiration
Show Answer
Answer: C – Chlorophyll absorbs light energy for photosynthesis, so a leaf short of chlorophyll captures less energy and its rate stays low.
Q12. In a required practical, a student counts bubbles from pondweed at different distances from a lamp. What is the student investigating?
- (A) The effect of temperature on respiration
- (B) The effect of carbon dioxide on transpiration
- (C) The effect of light intensity on the rate of photosynthesis
- (D) The effect of pH on enzyme activity
Show Answer
Answer: C – Bubble counts from pondweed give a measure of oxygen released, so changing the lamp distance varies light intensity and shows its effect on photosynthesis rate.
Aerobic and Anaerobic Respiration
Q13. Which word equation summarises aerobic respiration?
- (A) Carbon dioxide plus water gives glucose plus oxygen
- (B) Glucose gives ethanol plus carbon dioxide
- (C) Glucose gives lactic acid plus oxygen
- (D) Glucose plus oxygen gives carbon dioxide plus water
Show Answer
Answer: D – Aerobic respiration uses oxygen to break down glucose completely, producing carbon dioxide and water and transferring energy for the cell.
Q14. Respiration is described as exothermic. What does this tell us about energy?
- (A) Energy is taken in from light
- (B) Energy is transferred outwards from the reaction for living processes
- (C) Energy is destroyed completely
- (D) Energy is stored only as starch in most ordinary cells when conditions stay suitable
Show Answer
Answer: B – Respiration is an exothermic reaction that continuously transfers the energy cells need, releasing it for processes such as movement and building molecules.
Q15. Which three uses of energy transferred by respiration are named in the specification?
- (A) Photosynthesis, transpiration, and translocation when conditions stay suitable
- (B) Building larger molecules, movement, and keeping warm
- (C) Digestion, excretion, and reproduction only
- (D) Growth, sweating, and sleeping only
Show Answer
Answer: B – Organisms need energy from respiration for chemical reactions that build larger molecules, for movement, and for keeping warm.
Q16. During a sprint, a runner’s muscles cannot get oxygen fast enough. Which type of respiration takes over in the muscles, and what product builds up?
- (A) Anaerobic respiration, producing lactic acid
- (B) Aerobic respiration, producing ethanol
- (C) Photosynthesis, producing glucose
- (D) Fermentation in the liver, producing starch
Show Answer
Answer: A – Without enough oxygen, muscle cells respire anaerobically, breaking glucose down to lactic acid and transferring much less energy than aerobic respiration.
Q17. Why does anaerobic respiration transfer much less energy than aerobic respiration?
- (A) Glucose is not broken down at all
- (B) The oxidation of glucose is incomplete, so less energy is released
- (C) Oxygen is produced instead of being used
- (D) Carbon dioxide blocks the reaction completely during normal activity
Show Answer
Answer: B – Because glucose is only partly broken down in anaerobic respiration, much of its energy remains locked in the products.
Q18. Yeast cells respiring without oxygen produce two products. What are they?
- (A) Lactic acid and water for the organism described
- (B) Glucose and oxygen
- (C) Ethanol and carbon dioxide
- (D) Starch and cellulose
Show Answer
Answer: C – Anaerobic respiration in plant and yeast cells breaks glucose down to ethanol and carbon dioxide, a process called fermentation in yeast.
Q19. A baker uses yeast to make bread rise. Which product of yeast fermentation causes the dough to rise?
- (A) Ethanol, which evaporates during baking
- (B) Lactic acid, which sours the dough
- (C) Oxygen gas, which fills the dough
- (D) Carbon dioxide gas, which forms bubbles in the dough
Show Answer
Answer: D – Carbon dioxide released by fermenting yeast forms bubbles that expand the dough, while ethanol is largely driven off during baking.
Q20. Which statement correctly compares aerobic and anaerobic respiration in muscle cells?
- (A) Aerobic respiration needs no oxygen and produces lactic acid
- (B) Aerobic respiration needs oxygen and transfers more energy, while anaerobic respiration needs no oxygen and transfers less
- (C) Anaerobic respiration needs oxygen and produces the most energy in this type of tissue over a short period of time in a healthy organism
- (D) Both types need oxygen and produce ethanol
Show Answer
Answer: B – The key contrasts are oxygen requirement, products and relative energy transfer: aerobic respiration is complete and energy-rich, anaerobic respiration is incomplete and energy-poor.
Response to Exercise and Metabolism
Q21. When a person starts exercising vigorously, what happens to heart rate, breathing rate and breath volume?
- (A) All three increase to supply muscles with more oxygenated blood
- (B) All three decrease to save energy
- (C) Heart rate rises but breathing rate falls
- (D) Heart rate falls while breath volume rises only
Show Answer
Answer: A – Exercise raises the demand for energy, so the heart pumps faster and breathing becomes faster and deeper, delivering more oxygen to working muscles.
Q22. After hard exercise stops, a person keeps breathing heavily for several minutes. What is this extra oxygen used for?
- (A) To make extra red blood cells at once
- (B) To convert lactic acid back to glucose in the liver
- (C) To photosynthesise in muscle cells
- (D) To store oxygen in the lungs permanently in a healthy organism
Show Answer
Answer: B – The oxygen debt is repaid after exercise as blood carries lactic acid to the liver, where it is converted back to glucose.
Q23. Muscle fatigue during long vigorous activity is linked to which build-up in the muscles?
- (A) A build-up of ethanol
- (B) A build-up of starch
- (C) A build-up of lactic acid from anaerobic respiration
- (D) A build-up of carbon dioxide from photosynthesis at ordinary temperatures
Show Answer
Answer: C – When oxygen supply cannot keep up, muscles respire anaerobically and lactic acid accumulates, making the muscles tired and less able to contract efficiently.
Q24. What is meant by metabolism?
- (A) The breakdown of food in the stomach only
- (B) The transport of sugars in the phloem only
- (C) The sum of all chemical reactions in a cell or organism
- (D) The division of cells by mitosis only
Show Answer
Answer: C – Metabolism is the sum of all reactions in a cell or organism, in which molecules are made or broken down.
Q25. Which of these is an example of a metabolic reaction that builds a larger molecule?
- (A) Converting glucose into starch for storage
- (B) Breaking proteins down into urea for excretion
- (C) Breaking glucose down in respiration
- (D) Breaking starch down into glucose for respiration
Show Answer
Answer: A – Building starch from glucose is an anabolic step in metabolism, while respiration and breakdown to urea are reactions that break molecules down.
Q26. Excess amino acids in the body are broken down. Which waste product is formed and excreted?
- (A) Ethanol
- (B) Urea
- (C) Lactic acid
- (D) Cellulose
Show Answer
Answer: B – In metabolism, amino acids that are not needed for proteins are broken down, and the nitrogen-containing waste is excreted as urea.
Q27. A student compares two athletes after the same sprint. One recovers quickly and the other breathes heavily for much longer. What does the longer recovery suggest?
- (A) The slower athlete relied more on anaerobic respiration and built up more lactic acid to clear
- (B) The slower athlete produced less lactic acid
- (C) The slower athlete photosynthesised during the sprint when conditions stay suitable in a typical living organism
- (D) The slower athlete stored more starch in the muscles
Show Answer
Answer: A – A larger oxygen debt means more lactic acid must be transported to the liver and converted back to glucose, so heavy breathing continues longer.
Q28. Which metabolic conversion lets an animal store glucose for later use in its liver and muscles?
- (A) Glucose converted to cellulose
- (B) Glucose converted to lactic acid
- (C) Glucose converted to urea
- (D) Glucose converted to glycogen
Show Answer
Answer: D – Animals store glucose as glycogen in liver and muscle cells, a storage molecule that can be broken back down to glucose when energy is needed.
Q29. During exercise, arteries supplying the muscles widen. What is the benefit of this change?
- (A) It reduces blood flow to the muscles
- (B) It increases the flow of oxygenated blood to the working muscles
- (C) It stops carbon dioxide leaving the muscles during normal activity
- (D) It lowers the breathing rate
Show Answer
Answer: B – Widening the arteries to active muscles lets more oxygenated blood reach them, matching their increased demand for aerobic respiration.
Q30. A plant is moved from bright light to shade. Which two rates are both expected to fall?
- (A) Photosynthesis rate, while respiration rate rises sharply
- (B) Respiration rate only, while photosynthesis stays the same
- (C) Transpiration rate only, while photosynthesis stays the same
- (D) Photosynthesis rate and transpiration rate
Show Answer
Answer: D – Less light means less energy for photosynthesis, and in shade the leaf is usually cooler with less evaporation, so transpiration also falls.
Work through any questions you missed again, then revise those areas before moving on to the next topic.