1. 1
   A student examined cells taken from the surface of a young root under a microscope and noticed that some cells had long, thin extensions projecting into the soil, greatly increasing their surface area. Water appeared to be moving from the soil into these cells.

   (a)

   What is the function of these extensions?

   [1 mark]

   • AIncreasing the uptake of water and mineral ions from the soil
   • BIncreasing the rate of photosynthesis in the root
   • CIncreasing gas exchange with the atmosphere
   • DAnchoring pollen grains during fertilisation

   (b)

   By which process does water mainly move from the soil into the cells described by the student?

   [1 mark]

   • AActive transport
   • BOsmosis
   • CPhagocytosis
   • DTranslocation

   (c)

   Explain how the large surface area of these cells, together with the process of osmosis, allows efficient uptake of water from the soil.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Researchers traced the pathway taken by water absorbed from the soil as it moved through a tomato plant towards a leaf, measuring water potential at several points along the way.

   (a)

   Which sequence correctly describes this pathway?

   [1 mark]

   • ARoot cortex cells, phloem, root hair cell, mesophyll cells
   • BXylem, root hair cell, phloem, mesophyll cells
   • CRoot hair cell, root cortex cells, xylem, mesophyll cells
   • DMesophyll cells, xylem, root cortex cells, root hair cell

   (b)

   The researchers found that mineral ions, such as nitrate ions, were sometimes absorbed into root hair cells even when their concentration was higher inside the cell than in the soil water. Which process explains this?

   [1 mark]

   • ATranspiration
   • BOsmosis
   • CSimple diffusion
   • DActive transport

   (c)

   Explain why active transport, rather than diffusion, is needed for the uptake of some mineral ions by root hair cells, and state what this process requires from the cell.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A gardener noticed that plants grown in waterlogged soil, where oxygen levels are very low, absorbed noticeably fewer mineral ions than plants grown in well-aerated soil, even though both types of soil provided similar amounts of water.

   (a)

   Explain this observation.

   [3 marks]

   (b)

   Suggest and explain four features of root hair cells that adapt them for the efficient uptake of water and mineral ions from soil.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A biology class modelled the entire journey of a water molecule through a sunflower plant, from the moment it entered a root hair cell in moist soil to the moment it left the plant as water vapour from a leaf.

   (a)

   Describe the pathway taken by water as it moves from the soil, through a root, stem and leaf, and out of the plant, explaining how water potential changes drive this movement at each stage.

   [6 marks]

   (b)

   The same class investigated what would happen if the soil around the sunflower plant became very dry. Explain the effects of dry soil on water uptake and transport through the plant, and discuss the immediate and longer-term responses of the plant to this water shortage.

   [6 marks]

   Total for question 4: 12 marks

End of questions