1. 1
   A student investigates how a tomato plant transports water and food around its body. The student cuts a thin cross-section through the stem and examines it under a microscope, identifying two types of transport tissue. The student notes that one tissue is composed of hollow tubes strengthened by a substance called lignin, while the other is composed of tubes of elongated living cells connected by pores in their end walls.

   (a)

   Which row correctly identifies the tissue and its main function?

   [1 mark]

   • AXylem — transports dissolved sugars from leaves to the rest of the plant
   • BPhloem — transports water and mineral ions from roots to stems and leaves
   • CXylem — transports water and mineral ions from roots to stems and leaves
   • DPalisade mesophyll — transports water in the transpiration stream

   (b)

   The student notices that the hollow, lignin-strengthened tubes are dead cells with no cell contents. Which feature of these cells best explains why they are well adapted for their transport function?

   [1 mark]

   • AThe absence of cell contents leaves a continuous, unobstructed tube for the mass flow of water
   • BThe absence of cell contents allows active transport of mineral ions using energy from respiration
   • CThe lignin makes the walls partially permeable, allowing osmosis to occur along the whole tube
   • DThe lignin breaks down the cellulose cell wall, widening the tube for sugar transport

   (c)

   Name the process by which dissolved sugars move through the living tissue described above, and state the direction in which the sugars move.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gardener places a potted plant on a windowsill and records the rate of water loss from its leaves over several days using a potometer. On the first day, conditions are cool, still and humid, with dim light. On the second day, the gardener moves an electric fan and a heater near the plant, opens a window to reduce humidity, and switches on a bright grow-light.

   (a)

   Which combination of conditions would produce the highest rate of transpiration from the leaf?

   [1 mark]

   • ALow temperature, still air, high humidity, low light intensity
   • BHigh temperature, moving air, low humidity, high light intensity
   • CHigh temperature, still air, high humidity, low light intensity
   • DLow temperature, moving air, low humidity, low light intensity

   (b)

   The gardener notices tiny pores on the underside of the leaves, each surrounded by a pair of specialised cells. What is the main role of these specialised cells?

   [1 mark]

   • AThey transport water directly from the roots to the pore
   • BThey carry out photosynthesis to supply glucose to the whole leaf
   • CThey produce lignin to strengthen the surrounding epidermal tissue
   • DThey control the opening and closing of the pore to regulate gas exchange and water loss

   (c)

   Explain why moving air across the leaf surface, as the gardener did with the electric fan, increases the rate of transpiration.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farmer notices that crops grown in dry, sandy soil have very few root hairs and appear to be wilting, despite the soil containing sufficient mineral ions. Soil scientists suggest that the sandy soil damages the delicate root hair cells as the roots grow through it.

   (a)

   Explain how the shape of a root hair cell is adapted to absorb water and mineral ions efficiently, and why a plant with fewer root hairs would struggle to take up enough water.

   [3 marks]

   (b)

   The farmer decides to test whether adding organic compost, which retains more water than sandy soil, improves root hair growth and water uptake. Describe how the farmer could investigate this scientifically, and explain one variable that must be controlled for the comparison to be valid.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A greenhouse manager grows lettuce plants and wants to maximise crop yield by encouraging the fastest possible healthy growth. The manager has read that both the internal structure of the plant and the external environmental conditions inside the greenhouse affect how efficiently the plant transports water and food.

   (a)

   Explain how water and mineral ions move from the soil, through the root, and up to the leaves of the lettuce plant, describing the structures and processes involved at each stage.

   [6 marks]

   (b)

   The greenhouse manager is deciding whether to install heaters, fans, humidifiers and supplementary lighting to control the rate of transpiration in the greenhouse. Evaluate how each of temperature, air movement, humidity and light intensity affects the rate of transpiration, and explain the risk of setting these factors too high for prolonged periods.

   [6 marks]

   Total for question 4: 12 marks

End of questions