AQA GCSE Biology
AQA GCSE Biology 4.4.1 Photosynthesis Exam Questions
Free AQA GCSE Biology exam questions for 4.4.1 Photosynthesis, with a mark scheme for every pack. Covers the photosynthesis reaction, factors affecting rate, limiting factors, the inverse square law, greenhouse economics and uses of glucose.
4.4.1 Photosynthesis exam questions
4 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Biology 4.4.1 Photosynthesis
Photosynthesis is the first half of AQA Bioenergetics, examined on Paper 1. It explains how plants and algae use light energy to make glucose from carbon dioxide and water, and what limits the rate. Higher tier students also need limiting factor graphs with more than one factor, the inverse square law for light intensity, and the economics of enhancing conditions in greenhouses. The required practical investigates the effect of light intensity on the rate of photosynthesis using pondweed. It links to leaf structure in 4.2.3, respiration in 4.4.2 and food chains in Ecology.
What you need to know
- 4.4.1.1 Photosynthetic reaction Photosynthesis is an endothermic reaction in which energy is transferred from the environment to chloroplasts by light. Word equation: carbon dioxide + water -> glucose + oxygen. Symbol equation: 6CO2 + 6H2O -> C6H12O6 + 6O2.
- 4.4.1.2 Rate of photosynthesis Temperature, light intensity, carbon dioxide concentration and the amount of chlorophyll all affect the rate. A limiting factor is the factor in shortest supply that stops the rate increasing.
- Limiting factors (Higher tier only) Interpret graphs where two or three factors limit the rate. On a plateau, increasing the plotted factor has no effect, so another factor is limiting.
- Inverse square law (Higher tier only) Light intensity is inversely proportional to the square of the distance from the light source: light intensity proportional to 1 / d^2. Doubling the distance reduces light intensity to a quarter.
- Greenhouse economics (Higher tier only) Growers raise temperature, light and carbon dioxide to increase yield, but must balance the extra cost of heating, lighting and gas against the extra profit from faster growth.
- Required practical: light intensity Place pondweed at different distances from a lamp and count oxygen bubbles or measure gas volume in a set time. Control temperature (use a water bath or LED) and carbon dioxide concentration.
- 4.4.1.3 Uses of glucose Glucose is used for respiration, converted to insoluble starch for storage, used to make fat or oil for storage, used to make cellulose for cell walls, and combined with nitrate ions from the soil to make amino acids for proteins.
Common mistakes in 4.4.1 Photosynthesis
- Saying photosynthesis is exothermic. It is endothermic because energy is taken in from light.
- Saying light energy is converted into glucose. Light energy is transferred to chemical energy stored in glucose.
- Saying high temperature kills the enzymes. Above the optimum, enzymes controlling photosynthesis are denatured.
- Halving instead of quartering. Under the inverse square law, doubling the distance makes the light intensity one quarter, not one half.
- Saying plants photosynthesise instead of respiring. Plants respire all the time; they photosynthesise only when light is available.
Try three 4.4.1 Photosynthesis exam-style questions
1. A lamp is moved from 10 cm to 30 cm from a plant. Calculate how many times lower the light intensity becomes. (2 marks)
Show the mark scheme answer
Distance increases by a factor of 3; intensity proportional to 1 / d^2 so it falls by 3^2 = 9 times (Higher tier only)
2. Explain why increasing the carbon dioxide concentration in a greenhouse may not increase the rate of photosynthesis. (2 marks)
Show the mark scheme answer
Another factor such as light intensity or temperature is limiting; so the rate is controlled by that factor and stays the same
3. Give three ways a plant uses the glucose made in photosynthesis. (3 marks)
Show the mark scheme answer
Respiration; converted to starch for storage; used to make cellulose for cell walls; used to make fats or oils for storage; combined with nitrate ions to make amino acids and protein (any three)
4.4.1 Photosynthesis FAQs
What does AQA GCSE Biology 4.4.1 Photosynthesis cover?
It covers the photosynthesis reaction, the factors that affect its rate, limiting factors, the inverse square law and greenhouse economics (Higher tier only), and how plants use glucose.
Which paper is 4.4.1 Photosynthesis examined on?
Bioenergetics is assessed on Paper 1.
What equations do I need for photosynthesis?
Learn the word and balanced symbol equations, and for Higher tier the inverse square law (light intensity proportional to 1 / distance squared). Rate is often calculated as volume of gas or number of bubbles divided by time.
