Question 1
Which row correctly shows the reactants and products of photosynthesis?
- Reactants: glucose and oxygen. Products: carbon dioxide and water.
- Reactants: carbon dioxide and water. Products: glucose and oxygen.
- Reactants: carbon dioxide and oxygen. Products: glucose and water.
- Reactants: glucose and water. Products: carbon dioxide and oxygen.
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Answer: B (1)
Question 2
Photosynthesis is an endothermic reaction. Describe what this means in terms of energy and where it is transferred to.
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- energy is transferred from the environment / surroundings (1) allow energy is taken in
- to the chloroplasts by light (1)
Question 3
A student measured the oxygen released by pondweed. (a) The pondweed released 18 cm³ of oxygen in 6 minutes. Calculate the rate of photosynthesis. Give the unit. (b) The lamp was moved closer and the rate increased to 4.5 cm³ per minute. Calculate how long it would now take the pondweed to release 18 cm³ of oxygen.
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- (a) rate = volume ÷ time = 18 ÷ 6 (1)
- 3 cm³ per minute / 3 cm³/min (1) allow 1 mark for correct working if the answer or the unit is wrong
- (b) time = volume ÷ rate = 18 ÷ 4.5 (1)
- 4 minutes (1) correct answer with no working scores 2
Question 4
Explain how an increase in temperature affects the rate of photosynthesis.
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- as temperature rises (to the optimum), the rate increases (1)
- because molecules move faster / collide more often (1) allow enzymes work faster; ignore more energy unqualified
- above the optimum temperature the rate falls (1)
- because enzymes are denatured / the shape of the active site changes (1)
Question 5
A graph shows the rate of photosynthesis against light intensity. The rate rises steeply, then becomes constant at high light intensities. Explain the shape of the graph. Name one factor that could be limiting the rate when the graph is flat.
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- at low light intensity, light intensity is the limiting factor (1)
- so increasing light intensity increases the rate (1)
- at the flat part, a different factor is limiting, for example carbon dioxide concentration / temperature / amount of chlorophyll (1)
Question 6
Higher tier (what this means)
Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels meanA graph shows the rate of photosynthesis against light intensity at two carbon dioxide concentrations, 0.04% and 0.12%, at the same temperature. At low light intensity the two lines are together. At higher light intensity the line for 0.04% levels off, but the line for 0.12% keeps rising. (a) Explain the shape of the 0.04% line. (b) Explain why the lines are together at low light intensity. (c) State the limiting factor for the 0.04% line at high light intensity.
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- (a) light intensity is limiting at first so the rate rises (1)
- then carbon dioxide concentration becomes the limiting factor / light no longer limiting so the line levels off (1)
- (b) at low light intensity light is the limiting factor for both, so carbon dioxide has no effect (1)
- (c) carbon dioxide concentration (1)
Question 7
Higher tier (what this means)
Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels meanA lamp placed 10 cm from a plant gives a light intensity of 80 arbitrary units. Calculate the light intensity when the lamp is 40 cm from the plant.
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- distance increases by a factor of 4 (1)
- so intensity decreases by a factor of 4² = 16 (1)
- 80 ÷ 16 = 5 (arbitrary) units (1)
Question 8
Higher tier (what this means)
Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels meanA grower uses a greenhouse to grow tomatoes. Evaluate whether it is worth the grower adding extra heating when the light intensity is the limiting factor.
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- when light intensity is limiting, increasing temperature will not increase the rate (1)
- so there is no increase in growth / yield (1)
- but the heating costs money (1)
- so the grower would lose profit / it is not cost effective (1) allow better to spend money on extra lighting, if cost-effective
Question 9
Describe how you would investigate the effect of light intensity on the rate of photosynthesis using pondweed. Include how you would control other variables.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | A clear, logical method that is easy to follow and replicate, including how light intensity is changed, how the rate is measured, and at least two control variables with how they are controlled. Results are repeated and a mean is taken. |
| 2 | 3–4 | A method with most steps, including how the light intensity is changed and the rate is measured, with some attempt to control a variable. Some steps may be missing or unclear. |
| 1 | 1–2 | A few relevant points, for example that a lamp is moved or bubbles are counted, but the method is incomplete or not in a logical order. |
Indicative content
- place pondweed in water in a beaker, with a lamp at a measured distance from the beaker
- change the distance of the lamp (independent variable) using a ruler, for example 10, 20, 30, 40, 50 cm
- measure the rate by counting bubbles of oxygen in a set time (for example one minute) or measuring the volume of gas collected
- repeat at each distance and calculate a mean
- control the temperature, for example using a water bath or heat shield between the lamp and the beaker
- control carbon dioxide, for example with sodium hydrogencarbonate in the water
- use the same piece of pondweed and the same time period
- allow the pondweed to adjust to each new distance before counting
Question 10
(a) State two ways in which a plant can use the glucose made in photosynthesis, other than for respiration. (b) Plants use nitrate ions to make proteins. State where plants absorb nitrate ions from.
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- (a) any two from: converted into starch for storage / used to produce fat or oil for storage / used to produce cellulose for cell walls / used to produce amino acids (1 each) ignore protein
- second correct use (1)
- (b) the soil (1)
Question 11
Which substance is made from glucose and strengthens the plant cell wall?
- Starch
- Cellulose
- Protein
- Oil
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Answer: B (1)