Factors affecting photosynthesisIB MYP Biology: Subtopic test

1. 1
   A student in Dubai grows basil in pots on a balcony. In summer the afternoon temperature on the balcony can rise above 45 °C, and in the early morning, just after sunrise, the light is dim. The student notices that the plants grow best in the spring.

   (a)

   What is a limiting factor in photosynthesis?

   [1 mark]

   • AThe factor present in the largest amount
   • BThe factor in shortest supply, which limits the rate of photosynthesis
   • CA waste product that builds up and stops photosynthesis
   • DA factor that is only needed at night

   (b)

   Just after sunrise the light is very dim. Which factor is most likely limiting the rate of photosynthesis then?

   [1 mark]

   • AOxygen concentration
   • BNitrogen concentration in the air
   • CWind speed
   • DLight intensity

   (c)

   Explain why the rate of photosynthesis of the basil falls when the temperature rises above about 40 °C.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student measures the rate of photosynthesis of a plant at 25 °C in air containing 0.04% carbon dioxide. From 0 to 40 arbitrary units (au) of light intensity the rate rises in a straight line from zero, reaching a rate of 8 units at 40 au. From 40 au to 100 au the rate stays at 8 units. At 80 au she then increases the carbon dioxide concentration to 0.1%, and the rate rises to 14 units.

   (a)

   At 70 au of light intensity, which statement is correct?

   [1 mark]

   • ALight intensity is not the limiting factor
   • BLight intensity is the limiting factor
   • CThe rate of photosynthesis is zero
   • DPhotosynthesis has stopped

   (b)

   Assuming the same conditions, what would the rate of photosynthesis be at 20 au?

   [1 mark]

   • A2 units
   • B8 units
   • C4 units
   • D10 units

   (c)

   Explain why the rate stayed at 8 units above 40 au, and why it then rose when the carbon dioxide concentration was increased.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates how light intensity affects the rate of photosynthesis of pondweed. She places a piece of pondweed in a beaker of water and shines a lamp on it from different distances. She counts the bubbles of gas released from the cut stem in one minute. She records 48 bubbles per minute at 10 cm from the lamp, 22 at 20 cm, 10 at 30 cm and 5 at 40 cm.

   (a)

   Describe how the student should carry out this investigation so that her results are valid.

   [3 marks]

   (b)

   Describe the trend in the results, calculate how many times greater the rate is at 10 cm than at 40 cm, explain the trend and evaluate the method of counting bubbles.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A farming cooperative in northern Norway wants to grow tomatoes in a large greenhouse all year round. In winter the days are very short and the outdoor temperature is often below 0 °C. The greenhouse could use electric lamps, gas heaters and a carbon dioxide supply, but these will make the tomatoes more expensive to produce.

   (a)

   Explain how the cooperative could use its knowledge of limiting factors to increase the yield of tomatoes in winter.

   [6 marks]

   (b)

   Discuss and evaluate whether the cooperative should spend money on lamps, heaters and carbon dioxide to grow tomatoes in winter.

   [6 marks]

   Total for question 4: 12 marks

End of questions