1. 1
   A student places a leafy shoot in water and attaches its cut stem to a capillary tube containing an air bubble, forming a simple potometer. As the plant transpires, water is drawn up the stem and the air bubble moves along the tube. The student records how far the bubble moves in five minutes under normal room conditions.

   (a)

   Which structure on the leaf is mainly responsible for controlling the loss of water vapour that causes the bubble to move?

   [1 mark]

   • AStomata
   • BXylem vessels
   • CRoot hair cells
   • DPhloem sieve tubes

   (b)

   Water moves from the roots to the leaves of the plant mainly through which tissue?

   [1 mark]

   • APhloem
   • BXylem
   • CCambium
   • DEpidermis

   (c)

   Explain how the movement of water shown by the bubble in the potometer is linked to transpiration from the leaves.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gardener has two identical potted plants of the same species and size. Plant 1 is kept in a still, cool greenhouse at 15°C with no air movement. Plant 2 is placed outdoors in warm, breezy conditions at 25°C. After one hour, the gardener weighs each pot and its plant to estimate the mass of water lost.

   (a)

   A gardener has two identical potted plants. Plant 1 is placed in a still, cool greenhouse. Plant 2 is placed outdoors in warm, breezy conditions. Which factor is most likely to make Plant 2 transpire faster than Plant 1?

   [1 mark]

   • ALower soil mineral content outdoors
   • BThicker cell walls in outdoor leaves
   • CIncreased air movement and higher temperature outdoors
   • DReduced number of chloroplasts outdoors

   (b)

   If the gardener moved Plant 1 into bright sunlight instead of the greenhouse, keeping the temperature and air movement the same, which change would you expect in its rate of transpiration?

   [1 mark]

   • AIt would decrease, as light causes stomata to close
   • BIt would increase, as light causes more stomata to open
   • CIt would stay the same, as light has no effect on stomata
   • DIt would stop completely, as light damages guard cells

   (c)

   Plant 2 lost 12 g of water in the hour described above. Calculate the mean rate of water loss for Plant 2 in grams per minute. Give your answer to two significant figures.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A gardener is growing tomato plants. During fruit development, the leaves continue photosynthesising while the growing tomatoes need a constant supply of sugars to grow. The gardener wants to understand how sugars produced in the leaves reach the fruits, and how this transport system differs from the one that supplies the plant with water.

   (a)

   Describe how sucrose made in the leaves of a fruiting tomato plant is transported to the developing tomato fruits, naming the tissue involved and the direction of transport.

   [3 marks]

   (b)

   The gardener notices that if a ring of bark (including the phloem) is removed from right around the tomato plant's stem, the leaves above the ring stay healthy but the fruits below the ring stop growing and eventually die. Explain these observations in terms of xylem and phloem function.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student sets up three identical potted plants, each with the same number of leaves, and measures the mass of water lost from each pot over one hour: Plant A is kept in still air at 20°C, Plant B is kept in moving air produced by a desk fan at 20°C, and Plant C is kept in still air at 35°C. All other conditions, including light intensity and soil moisture, are kept the same for all three plants.

   (a)

   A student sets up three identical potted plants and measures water loss over one hour under different conditions: Plant A in still air at 20°C, Plant B in moving air (from a fan) at 20°C, and Plant C in still air at 35°C. Explain, in terms of stomata, water vapour concentration gradients and diffusion, why Plant B and Plant C are both expected to lose more water than Plant A.

   [6 marks]

   (b)

   The student wants to make this investigation a fair and reliable test of the effect of air movement and temperature on transpiration rate. Evaluate the design described above, identifying two possible weaknesses and suggesting an improvement for each that would make the results more valid.

   [6 marks]

   Total for question 4: 12 marks

End of questions