Pearson Edexcel International A Level Biology: Photosynthesis (YBI11) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover statements 5.1 to 5.8 (photosynthesis, including Core Practical 10) of the Pearson Edexcel International Advanced Subsidiary/Advanced Level Biology specification (YBI11), Issue 2. Topic 5 is International A2 (IA2) and there are no tiers. Learn the content in the study guide and revision notes first. The course hub and checklist show the wider course.

Questions

1. State where the oxygen released in photosynthesis comes from, and describe what happens to the hydrogen from that source. [3]

2. Distinguish between photophosphorylation and the hydrolysis of ATP. [3]

3. Compare cyclic and non-cyclic photophosphorylation. [4]

4. A suspension of isolated chloroplasts fixes 7.2 µmol of carbon dioxide in a Calvin cycle. (a) Calculate the amount of ATP and of reduced NADP needed. [3] (b) Calculate the amount of glucose that could be made. [2]

5. A culture of unicellular algae in bright light is placed in darkness. Within one minute the GP level rises and the RuBP level falls. Explain these changes. [4]

6. Explain how three features of a chloroplast help it to carry out photosynthesis. [5]

7. The table shows the rate of oxygen release by a pondweed at different wavelengths, and the absorbance of a leaf pigment extract.

Wavelength (nm)	400	450	500	550	600	650	700
Rate (arbitrary units)	30	78	42	20	35	70	12
Absorbance	0.62	0.82	0.30	0.12	0.25	0.70	0.08

(a) Define the terms action spectrum and absorption spectrum. [2] (b) Calculate the rate at 550 nm as a percentage of the rate at 450 nm. [1] (c) Explain what the data show about the relationship between absorption and photosynthesis. [3]

8. A leaf extract was separated by chromatography in a propanone-based solvent. The solvent front moved 9.0 cm. Four pigments moved 8.1, 6.3, 4.5 and 3.6 cm. (a) Calculate the Rf value of each pigment. [2] (b) Explain why the pigments separate. [2] (c) State how the pigments could be identified. [1]

9. Describe how you would investigate the effect of temperature on the rate of photosynthesis of Canadian pondweed. [7]

10. In an investigation of light intensity, a lamp was placed at four distances from a pondweed shoot. The number of bubbles in 2 minutes was counted.

Distance (cm)	10	20	30	40
Bubbles in 2 minutes	52	15	7	4

(a) Calculate the rate in bubbles per minute at each distance. [1] (b) Calculate how many times greater the light intensity is at 10 cm than at 20 cm. [1] (c) Describe and explain the trend, and suggest why the rate at 10 cm is less than four times the rate at 20 cm. [4]

11. State how the sugars made in photosynthesis are used by plants, animals and other organisms. [4]

Answers

1. The oxygen comes from water [1], split by photolysis in the light-dependent reactions [1]. The hydrogen (H⁺ and electrons) is used to reduce NADP and is then used to reduce GP and so is stored in glucose [1]. [3] Examiner insight: A common slip is naming carbon dioxide as the source of oxygen, which is wrong. Say where the hydrogen ends up, not only where it comes from.

2. Photophosphorylation joins ADP and Pi to make ATP [1], using energy from light (excited electrons) [1]. Hydrolysis of ATP splits it to ADP and Pi, releasing energy for processes such as active transport [1]. [3] Examiner insight: Answers that only say ATP “gives energy” without naming ADP and Pi are too vague. Describe both reactions in terms of their reactants and products.

3. Similarity: both make ATP [1]. Cyclic uses only PSI whereas non-cyclic uses PSII and PSI [1]. Cyclic does not produce reduced NADP or oxygen, whereas non-cyclic does (photolysis of water) [1]. In cyclic, electrons return to PSI, whereas in non-cyclic they are replaced by electrons from water [1]. [4] Examiner insight: A comparison needs both sides stated for each point. Writing only “cyclic does not make oxygen” leaves half of the comparison missing.

4. (a) ATP per CO₂ = 3, so 7.2 × 3 = 21.6 µmol ATP [1]. Reduced NADP per CO₂ = 2, so 7.2 × 2 = 14.4 µmol [1]. Reasoning: 2 GP per CO₂ are reduced (2 ATP, 2 reduced NADP) and RuBP regeneration adds 1 ATP per CO₂ fixed [1]. (b) 6 CO₂ are needed for each glucose [1], so 7.2 ÷ 6 = 1.2 µmol glucose [1]. [5] Examiner insight: Show the per-CO₂ figures before multiplying, so that the reader can see your reasoning clearly. Give units.

5. In the dark, ATP and reduced NADP are no longer made by the light-dependent reactions [1]. GP cannot be reduced to GALP, so GP accumulates [1]. RuBP is still being used to fix CO₂ by RUBISCO [1] but it cannot be regenerated from GALP without ATP, so RuBP falls [1]. [4] Examiner insight: State the cause (loss of ATP and reduced NADP) before the effect on each compound. Explaining GP and RuBP separately avoids vague statements.

6. Thylakoid membranes give a large surface area [1] for many photosystems and ATP synthase molecules [1]. Grana pack the photosystems closely for light capture, linked by lamellae [1]. Stroma contains the enzymes (such as RUBISCO) for the Calvin cycle, next to the thylakoids [1]. The small thylakoid space allows a steep H⁺ gradient to build up [1]. [5] Examiner insight: Each feature needs a linked function. A list of structure names alone does not explain anything.

7. (a) An action spectrum is a graph of the rate of photosynthesis against wavelength [1]. An absorption spectrum is a graph of the absorbance of a pigment against wavelength [1]. (b) 20 ÷ 78 × 100 = 26% [1]. (c) Both peak in blue (about 450 nm) and red (about 650 nm) [1], so the wavelengths best absorbed are those that give the highest rate [1]. The shapes are not identical, for example rate at 500 nm is higher than absorbance alone suggests, so accessory pigments or other effects may pass energy on to the photosystems [1]. [6] Examiner insight: Quote values from the table when describing the trend, and state the relationship rather than just describing each curve in turn.

8. (a) 8.1 ÷ 9.0 = 0.90 and 6.3 ÷ 9.0 = 0.70 [1]; 4.5 ÷ 9.0 = 0.50 and 3.6 ÷ 9.0 = 0.40 [1] (b) The pigments differ in solubility in the solvent [1] and in how strongly they are attracted to the paper, so they move at different rates [1]. (c) Compare the Rf values with known reference values for the same solvent and paper [1]. [5] Examiner insight: Rf has no units. Showing the division makes your method clear. Marking the solvent front before it dries avoids an unreliable value.

9. Set up a lamp at a fixed distance, with a heat shield, and a shoot of pondweed in a tube [1]. Use a water bath at a set temperature, for example 10 °C, and measure it with a thermometer [1]. Add sodium hydrogencarbonate solution so that CO₂ is not limiting [1]. Leave the plant for a few minutes to adjust [1]. Count the bubbles for a fixed time, for example 3 minutes, or measure gas volume in a capillary [1]. Repeat at several temperatures such as 10, 20, 30, 40 °C, with the same shoot and the same light each time [1]. Repeat each temperature and calculate a mean rate [1]. [7] Examiner insight: Give a range with enough values, and say how each controlled variable is held constant rather than listing it. A plan that has two variables changing cannot support a conclusion.

10. (a) 26, 7.5, 3.5, 2.0 bubbles per minute [1]. (b) (20 ÷ 10)² = 4 times [1]. (c) The rate falls as the lamp moves away [1], because light intensity falls and light is limiting the light-dependent reactions, so less ATP and reduced NADP are made [1]. The rate would be 4 × 7.5 = 30 bubbles per minute if proportional, but is 26 [1], so another factor such as CO₂ concentration or temperature is probably limiting at high intensity [1]. [6] Examiner insight: Use the figures from the table in the comparison. Writing the factor as “limiting” is more convincing if you say which stage it limits.

11. Used in respiration to release energy (in plants, animals and other organisms) [1]. Converted to polysaccharides such as starch and cellulose [1]. Used with nitrate to make amino acids and so proteins, and to make lipids [1]. Used to make the components of nucleic acids [1]. [4] Examiner insight: Naming one product from each class of molecule gains more than repeating respiration. Say “animals obtain the sugars by feeding” if the question mentions animals.

Where marks are usually lost

• Stating that the oxygen released comes from carbon dioxide.
• Describing ATP as “energy” instead of as a molecule that releases energy when hydrolysed.
• Missing the reduced NADP and oxygen difference in cyclic and non-cyclic comparisons.
• Saying the light-independent stage “needs no light” without linking it to ATP and reduced NADP.
• Explaining a change in GP or RuBP without naming ATP, reduced NADP or CO₂.
• Listing chloroplast structures with no function.
• Calculating Rf with units or measuring to the edge of the spot.
• Not saying how the other variables are controlled in a practical.

Next steps

• Revision notes
• Study guide
• Edexcel A Level Biology hub
• Printable checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

Pearson Edexcel International Advanced Subsidiary/Advanced Level Biology (YBI11) specification, Issue 2, published by Pearson Education Limited.