1. 1
   During a summer heatwave, a gardener notices that the leaves of the plants in the garden begin to wilt during the hottest part of the afternoon.

   (a)

   Which structures in a leaf allow gases to be exchanged between the plant and the air?

   [1 mark]

   • AStomata
   • BXylem
   • CRoot hairs
   • DPetals

   (b)

   Which cells control the opening and closing of stomata?

   [1 mark]

   • APalisade cells
   • BGuard cells
   • CEpidermal cells
   • DRoot hair cells

   (c)

   Explain why the plant's stomata close during the hottest, driest part of the afternoon.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An ecologist is measuring the concentration of gases entering and leaving the leaves of trees in a woodland over a full 24-hour period, comparing daytime and night-time readings.

   (a)

   During a bright, sunny day, which gas is released by a plant as a net product through its stomata?

   [1 mark]

   • ACarbon dioxide
   • BHydrogen
   • CNitrogen
   • DOxygen

   (b)

   At night, when photosynthesis stops but respiration continues, which gas is released by the plant through its stomata?

   [1 mark]

   • AOxygen
   • BNitrogen
   • CCarbon dioxide
   • DWater vapour only, with no gas exchange

   (c)

   Explain why the trees are a net absorber of carbon dioxide during the day but a net producer of carbon dioxide at night.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student is comparing the number of stomata on the upper and lower surfaces of leaves from different plants as part of a school investigation.

   (a)

   Describe how a student could estimate the number of stomata on the lower surface of a leaf without needing to look at any images.

   [3 marks]

   (b)

   Explain why most plants have more stomata on the lower surface of their leaves than on the upper surface.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A biology teacher is showing a class how plants regulate gas exchange and water loss through their leaves in response to changing environmental conditions.

   (a)

   Describe the process of gas exchange in plants through the stomata, including the movement of oxygen, carbon dioxide and water vapour, and the structure of guard cells.

   [6 marks]

   (b)

   Explain how guard cells open and close the stomata in response to changes in light intensity and water availability, and why this matters for both photosynthesis and water conservation.

   [6 marks]

   Total for question 4: 12 marks

End of questions