Overview of photosynthesis and ATPEdexcel International A Level Biology: Subtopic test

1. 1
   Algae were supplied with water that contained the heavy isotope ¹⁸O (H₂¹⁸O) and with carbon dioxide that contained only the normal isotope ¹⁶O. The algae were illuminated and the oxygen gas that they released was collected and analysed.

   (a)

   The oxygen gas released by the algae contained ¹⁸O. What does this show?

   [1 mark]

   • AOxygen gas is released from carbon dioxide
   • BOxygen gas is released from glucose
   • COxygen gas is released by chlorophyll
   • DOxygen gas is released from water

   (b)

   What happens to the hydrogen from the water in photosynthesis?

   [1 mark]

   • AIt is used to reduce carbon dioxide, so it is stored in glucose
   • BIt is released as hydrogen gas
   • CIt is used to form ATP from ADP and inorganic phosphate
   • DIt is released with the oxygen as hydrogen peroxide

   (c)

   The experiment was repeated with water containing only ¹⁶O and carbon dioxide containing ¹⁸O. Predict where the ¹⁸O would be found. Explain your answer.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hummingbird hovers in front of a flower while it feeds. Its flight muscles use ATP at a very high rate, but each muscle cell contains only enough ATP for a few seconds of activity.

   (a)

   Which equation represents the hydrolysis of ATP?

   [1 mark]

   • AADP + Pi → ATP + H₂O
   • BATP → ADP + Pi + H₂O
   • CATP + H₂O → ADP + Pi
   • DATP + Pi → ADP + H₂O

   (b)

   Why is ATP a suitable immediate source of energy for the flight muscles?

   [1 mark]

   • AIt is stored in large quantities in muscle cells
   • BIt releases energy in small amounts, in a single-step reaction
   • CIt is a long-term energy store
   • DIt releases energy only when it is converted to glucose

   (c)

   Explain how the hummingbird's muscles can keep contracting rapidly, although the amount of ATP in each cell is small.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Chloroplasts were isolated from leaf cells and placed in a suspension that contained ADP, inorganic phosphate and a compound that accepts hydrogen. When the suspension was illuminated, oxygen was released and ATP was formed. In darkness, neither oxygen nor ATP was produced.

   (a)

   Explain these observations.

   [3 marks]

   (b)

   In a second experiment, carbon dioxide was supplied and the chloroplasts released 0.45 mmol of oxygen in the light. The overall equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Calculate the maximum mass of glucose (relative formula mass 180) that could have been made. Suggest one reason why the mass of glucose collected would be lower than your calculated value.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student states: 'Photosynthesis stores light energy in glucose, so plant cells can use the glucose directly to power all their reactions. Plant cells therefore do not need ATP.'

   (a)

   Describe and explain how photosynthesis converts light energy into chemical energy. In your answer, refer to the roles of water, carbon dioxide and ATP.

   [6 marks]

   (b)

   Evaluate the student's statement.

   [6 marks]

   Total for question 4: 12 marks

End of questions