1. 1
   A student places a sprig of pondweed in a beaker of water under a bright lamp. Bubbles of gas begin to stream from the cut end of the stem. The student collects the gas in an upturned test tube and, after several minutes, tests it with a glowing splint. The splint relights when inserted into the tube.

   (a)

   Which gas is used by the pondweed as a raw material for photosynthesis?

   [1 mark]

   • ACarbon dioxide
   • BOxygen
   • CNitrogen
   • DHydrogen

   (b)

   Which result of the glowing splint test confirms the identity of the gas collected?

   [1 mark]

   • AThe splint is extinguished immediately
   • BThe splint relights and burns brightly
   • CThe splint produces a squeaky pop
   • DThe splint turns limewater cloudy

   (c)

   Write the word equation for the reaction taking place in the pondweed and explain why this reaction is described as endothermic.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A class investigates the effect of light intensity on the rate of photosynthesis using pondweed. Three identical beakers of pondweed in water containing dissolved sodium hydrogencarbonate are set up, each at a different distance from an identical lamp: 10 cm, 30 cm and 50 cm. Temperature is kept constant using a water bath, and the number of bubbles released per minute is counted for each beaker.

   (a)

   In the third beaker, which factor is limiting the rate of photosynthesis?

   [1 mark]

   • ACarbon dioxide concentration
   • BLight intensity
   • CTemperature
   • DWater availability

   (b)

   Why is sodium hydrogencarbonate dissolved in the water in each beaker?

   [1 mark]

   • ATo provide a constant supply of carbon dioxide
   • BTo provide a constant supply of oxygen
   • CTo keep the water at a constant temperature
   • DTo kill any microorganisms in the water

   (c)

   The beaker at 10 cm produced far more bubbles per minute than the beaker at 50 cm. Explain this difference in terms of light intensity and the rate of photosynthesis.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A research group grows identical pondweed samples at three fixed temperatures: 10°C, 20°C and 30°C. At each temperature, they measure the rate of photosynthesis while gradually increasing light intensity, keeping carbon dioxide concentration constant throughout. At all three temperatures, the rate of photosynthesis increases with light intensity at first, then levels off at a plateau. The plateau is reached at a lower light intensity for the 10°C samples than for the 20°C or 30°C samples.

   (a)

   Describe how the researchers could use this data to determine whether light intensity or carbon dioxide concentration is the limiting factor at each temperature.

   [3 marks]

   (b)

   Explain why the plateau is reached at a lower light intensity for the 10°C samples than for the 30°C samples, and suggest what would happen to the rate of photosynthesis if the temperature were increased further to 45°C.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A commercial greenhouse grower cultivates tomato plants year-round. During winter, natural daylight is weak and the outside temperature is low, while the greenhouse remains largely sealed to conserve heat. The grower is considering installing supplementary lighting, a heating system, and a carbon dioxide enrichment system, but has a limited budget and can only afford to install one of these systems this winter.

   (a)

   A greenhouse grower wants to maximise the rate of photosynthesis, and therefore biomass production, of tomato plants during winter, when natural light is weak and cold. Explain how each of temperature, light intensity and carbon dioxide concentration could be acting as limiting factors on photosynthesis in this greenhouse in winter, and how the interaction of these three factors together determines the overall rate.

   [6 marks]

   (b)

   Using the inverse square law, explain how doubling the distance between a supplementary lamp and the tomato plants would affect the light intensity reaching the plants and hence the rate of photosynthesis, and evaluate whether installing supplementary lighting alone is the grower's best choice given the limited budget.

   [6 marks]

   Total for question 4: 12 marks

End of questions