Bioenergetics
Bioenergetics is the GCSE biology topic covering photosynthesis, the process by which plants and algae use light energy to make glucose from carbon dioxide and water, and respiration, the process that releases energy from glucose in all living cells. It includes the required practical on light intensity and the rate of photosynthesis in pondweed.
Method
- Learn the word and balanced symbol equations for photosynthesis (carbon dioxide + water -> glucose + oxygen), and know that it is endothermic, taking in light energy.
- Learn the three limiting factors of photosynthesis (light intensity, carbon dioxide concentration, temperature), and be able to explain from a graph which factor is limiting the rate at a given point.
- For the pondweed required practical, use the inverse square relationship between light intensity and distance: relative light intensity = 1 / distance^2, and be ready to rearrange it to find distance.
- Learn the word and symbol equations for aerobic respiration (glucose + oxygen -> carbon dioxide + water), and know it is exothermic, releasing energy the cell can use.
- Learn the difference between aerobic respiration and the two types of anaerobic respiration: in muscle cells glucose is only partly broken down into lactic acid, while in yeast and plant cells glucose is broken down into ethanol and carbon dioxide.
- For extended-response questions on exercise, link changes in heart rate, breathing rate and breathing depth to an increased rate of aerobic respiration, and describe oxygen debt as the extra oxygen needed after exercise to break down lactic acid.
Worked example
A student investigates the effect of light intensity on the rate of photosynthesis of pondweed by changing the distance of a lamp from the plant. Calculate the relative light intensity when the lamp is placed 25 cm from the pondweed, using the equation: relative light intensity = 1 / distance^2.
- Write down the equation: relative light intensity = 1 / distance^2.
- Substitute the distance: relative light intensity = 1 / 25^2.
- Calculate 25^2 = 625.
- Calculate 1 / 625 = 0.0016.
- Final answer: the relative light intensity is 0.0016 (arbitrary units).
Practice questions
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Q1Name the gas that is released as a product of photosynthesis.Show answer
Answer: Oxygen.
Q2Name the organelle in a plant cell where photosynthesis takes place.Show answer
Answer: The chloroplast.
Q3State three factors that can limit the rate of photosynthesis.Show answer
Answer: Light intensity, carbon dioxide concentration, and temperature.
Q4Complete the word equation for anaerobic respiration in yeast: glucose -> ___ + ___Show answer
Answer: Ethanol and carbon dioxide.
Q5A lamp is placed 10 cm from pondweed. Calculate the relative light intensity using relative light intensity = 1 / distance^2.Show answer
Answer: 0.01 (1/10^2 = 1/100)
Q6Explain why anaerobic respiration releases much less energy per glucose molecule than aerobic respiration.Show answer
Answer: Glucose is only partially broken down (into lactic acid, or into ethanol and carbon dioxide) rather than fully broken down into carbon dioxide and water, so much less of the energy stored in the glucose is released.
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
State whether photosynthesis is exothermic or endothermic, and explain your answer in terms of energy transfer.
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A student calculates that the relative light intensity reaching a piece of pondweed is 0.015625 when the lamp is 8 cm away. The student wants to increase the relative light intensity to 0.0625, four times greater. Calculate the new distance the lamp should be placed from the pondweed.
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When a person exercises vigorously, their leg muscles need extra energy from aerobic respiration. Explain how changes in heart rate, breathing rate and breathing depth during exercise help to meet this increased energy demand.
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Free printable worksheet
Want more practice on paper? Download the bioenergetics worksheet pack - 17 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 4 of GCSE Biology Workbook, the whole course as one free printable PDF.
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