6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
Learn this properly: PhotosynthesisA gardener grows tomato plants inside a greenhouse and wants them to photosynthesise as fast as possible.
Explain how light intensity, carbon dioxide concentration and temperature can each act as a limiting factor on the rate of photosynthesis. (6 marks)
In Core Practical 6, a student used a potometer to measure the rate of water uptake by a leafy shoot. They recorded how far an air bubble moved along the capillary tube in a fixed time, under still air and in front of a fan.
| Condition | Distance bubble moved / mm | Time / minutes |
|---|---|---|
| Still air | 24 | 8 |
| In front of a fan | 60 | 8 |
(a) Calculate the rate of water uptake, in mm/min, for the shoot in still air. Show your working. (2 marks)
(b) Explain why the rate of water uptake was higher in front of the fan. (2 marks)
A potted plant is placed near a window so that light reaches it from one side only. After a few days, the shoot has bent so that it is growing towards the light.
Explain, in terms of the plant hormone auxin, how the shoot bends towards the light. (3 marks)
Plants have two transport tissues: xylem and phloem.
(a) Name the substance transported in the phloem from the leaves to other parts of the plant. (1 mark)
(b) Give two ways in which transport in the phloem differs from transport in the xylem. (2 marks)
On a hot, dry day a plant loses water from its leaves much faster than on a cool, humid day.
Explain why a low humidity in the surrounding air increases the rate of transpiration. (2 marks)
Plant growth responses to a directional stimulus, such as a shoot growing towards light, are controlled by a plant hormone.
Name the plant hormone mainly responsible for controlling phototropism in shoots. (1 mark)