GCSE BiologyAQA, Edexcel and OCR
12 biology questions on photosynthesis. Pick your answer, then tap to see if you were right and why. Every answer comes from the Show Working science bank, checked against the GCSE content every board in England teaches.
01 / Quiz yourselfTry it, then tap to check
Choose your answer before you open it. Then read why, so it sticks.
01 / PhotosynthesisBoth tiers
Answer: C carbon dioxide and water
Photosynthesis turns carbon dioxide and water into glucose and oxygen, using energy from light. Glucose is made by the reaction, so it is a product, not a reactant.
Checked against OpenStax Biology 2e, 8.1 Overview of Photosynthesis
02 / PhotosynthesisBoth tiers
Answer: B the chloroplasts
Photosynthesis takes place in the chloroplasts. They contain chlorophyll, a green pigment that absorbs light, and that light supplies the energy for the reaction.
Checked against OpenStax Biology 2e, 8.1 Overview of Photosynthesis
03 / PhotosynthesisBoth tiers
Answer: B It takes in energy from its surroundings
Photosynthesis is endothermic: energy is transferred from the environment to the chloroplasts by light. That energy ends up stored in the glucose the plant makes.
Checked against OpenStax Biology 2e, 8.1 Overview of Photosynthesis
04 / PhotosynthesisBoth tiers
Answer: D C₆H₁₂O₆
In symbols, photosynthesis takes in CO₂ and H₂O and makes C₆H₁₂O₆ (glucose) and O₂ (oxygen). The oxygen is released into the air.
Checked against OpenStax Biology 2e, 8.1 Overview of Photosynthesis
05 / PhotosynthesisBoth tiers
Answer: D They make their own food by photosynthesis
Plants and algae make glucose by photosynthesis and use it to build their bodies. That biomass is the food for almost every other living thing, so food chains start with a producer.
Checked against OpenStax Biology 2e, 46.1 Ecology of Ecosystems
06 / PhotosynthesisBoth tiers
Answer: D as insoluble starch
Plants turn some of their glucose into insoluble starch to store it, and some into cellulose for cell walls. This is how photosynthesis builds biomass. Glycogen is the store in animals, not plants.
Checked against OpenStax Biology 2e, 8.3 Using Light Energy to Make Organic Molecules
07 / PhotosynthesisBoth tiers
Answer: D It increases
Light provides the energy for photosynthesis, so more light gives a faster rate. Eventually the rate stops rising, because something else, such as carbon dioxide or temperature, holds it back.
Checked against OpenStax Biology 2e, 8.1 Overview of Photosynthesis
08 / PhotosynthesisBoth tiers
Answer: C Carbon dioxide is a reactant
Carbon dioxide is one of the reactants, so more of it lets the reaction run faster. Air has only about 0.04% carbon dioxide, so it often limits how fast plants can photosynthesise.
Checked against OpenStax Biology 2e, 8.3 Using Light Energy to Make Organic Molecules
09 / PhotosynthesisBoth tiers
Answer: A The enzymes are denatured
Photosynthesis is controlled by enzymes. Warmth speeds them up, but above the optimum their active sites change shape: they are denatured and the rate falls. Enzymes are not alive, so they are never killed.
Checked against OpenStax Biology 2e, 8.3 Using Light Energy to Make Organic Molecules
10 / PhotosynthesisHigher only
Answer: A The factor in shortest supply
The rate can only go as fast as the scarcest factor allows. Raising that factor speeds the reaction up; raising the others does nothing until it is no longer the one in shortest supply.
Checked against OpenStax Biology 2e, 8.1 Overview of Photosynthesis
11 / PhotosynthesisHigher only
Answer: A carbon dioxide
Where the curve goes flat, light is no longer the limiting factor: something else, such as carbon dioxide or temperature, is. Raising the carbon dioxide lifts the flat part, which shows carbon dioxide was limiting.
Checked against OpenStax Biology 2e, 8.1 Overview of Photosynthesis
12 / PhotosynthesisHigher only
Answer: A carbon dioxide
In a closed greenhouse on a warm, bright day, plants soon use up the carbon dioxide, so it limits the rate. Growers add heat, light or carbon dioxide only where it is limiting and the extra crop pays for the cost.
Checked against OpenStax Biology 2e, 8.1 Overview of Photosynthesis
02 / Longer answersMarked by levels
Write your answer first, on paper. Then open it and tick off the points you made. How 6-mark questions are marked.
6 marks / Adding carbon dioxide to a greenhouseHigher only
A tomato grower keeps a greenhouse at 25 °C all winter and plans to pump in extra carbon dioxide every day, which costs money. Tests in the greenhouse showed that on dull days extra light raised the rate of photosynthesis but extra carbon dioxide made almost no difference. On bright days extra carbon dioxide raised the rate a lot.
The rate of photosynthesis is controlled by whichever factor is in shortest supply, which is called the limiting factor. On dull winter days the tests show that light intensity is the limiting factor, because extra light raised the rate but extra carbon dioxide did not. So on dull days the plants cannot use the extra carbon dioxide, and the money spent on it is wasted. On bright days light is no longer limiting, and carbon dioxide becomes the limiting factor, so adding carbon dioxide does increase the rate. A faster rate of photosynthesis produces more glucose, which the plants use for growth, so the grower should get a bigger crop of tomatoes on those days. The temperature is already kept at 25 °C, which is close to the optimum for the enzymes involved, so it should not be limiting. However, the grower must make sure that the extra tomatoes are worth more than the cost of the carbon dioxide and the heating. Overall, adding carbon dioxide every day is not a good plan. It would be better to add it only on bright days, or to add lamps as well if the extra crop pays for the electricity.
Assuming that adding more of any factor always speeds up photosynthesis. Only raising the limiting factor increases the rate, and in an evaluate question you must weigh the extra crop against the cost and give a conclusion.
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