1. 1
   A biology student examines two samples of plant tissue extracted from a stem. Sample X consists of dead, hollow cells with thickened walls containing a strengthening substance called lignin, joined end to end with no cross walls to form long continuous tubes. Sample Y consists of living cells arranged in tubes with partially perforated end walls, through which a sugary sap can flow.

   (a)

   Sample X, made of dead, hollow, lignified cells joined into continuous tubes, is best described as which tissue?

   [1 mark]

   • APhloem
   • BCambium
   • CEpidermis
   • DXylem

   (b)

   Sample Y, made of living cells with perforated end walls carrying sugary sap, mainly transports which substances?

   [1 mark]

   • AWater and mineral ions
   • BOxygen and carbon dioxide
   • CSucrose and amino acids
   • DStarch and cellulose

   (c)

   Explain how the structure of sample X, being dead, hollow, lignified and joined end to end with no cross walls, relates to its function of transporting water and providing support.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A garden centre worker is advising a customer who has just transplanted young tomato seedlings into a bed of garden soil. The worker explains how the tiny root hairs on the seedlings' roots take up the water the plants need over the following days as they establish themselves.

   (a)

   Root hair cells increase the uptake of water and mineral ions from the soil mainly because of which feature?

   [1 mark]

   • ATheir large surface area
   • BTheir thick cell walls
   • CTheir green colour
   • DTheir large vacuole alone

   (b)

   After entering a root hair cell, water passes through which structures, in this order, before reaching the xylem?

   [1 mark]

   • ALeaf mesophyll cells, then xylem
   • BPhloem, then xylem
   • CRoot cortex cells, then xylem
   • DStomata, then xylem

   (c)

   Explain why newly transplanted seedlings, whose fine root hairs may have been damaged during transplanting, often wilt slightly for a few days afterwards even if the soil is kept moist.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A houseplant is placed directly in front of an air conditioning unit that blows a constant stream of cool, dry air across it. Within a day its leaves begin to droop, while an identical houseplant kept elsewhere in the same room, away from the air conditioning unit, remains healthy.

   (a)

   Explain, referring to wind speed and air humidity, why the plant near the air conditioning unit loses water through transpiration faster than the other plant.

   [3 marks]

   (b)

   Describe the process of transpiration, from the evaporation of water inside the leaf to its loss as water vapour, and explain why drooping leaves are a visible sign that a plant is losing water faster than its roots can replace it.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A biology class studying transport in plants is given two related scenarios: a greenhouse technician tracing how water taken up by a young maize seedling's roots eventually reaches the air outside its leaves on a hot, sunny day, and an arborist explaining how a giant redwood tree, whose topmost leaves sway high overhead in the wind, achieves the same feat on a far larger scale, without anything resembling a pump inside its trunk.

   (a)

   For the maize seedling, explain, in order, the pathway taken by a water molecule from the soil, through the root, stem and leaf, to its eventual loss from the plant on this hot day.

   [6 marks]

   (b)

   For the redwood tree, explain the mechanism, often called transpiration pull, by which water is drawn upwards through the xylem to its highest leaves without any pump, referring to forces between water molecules and to the structure of xylem vessels.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A strawberry farmer notices that the runners produced by her mature strawberry plants carry small plantlets, which grow roots of their own within a few weeks. Before this happens, the young plantlets rely entirely on the mother plant for the sugars and amino acids they need to grow.

   (a)

   Sucrose and amino acids are carried from the mother plant to the young plantlet mainly through which tissue?

   [1 mark]

   • AXylem
   • BPhloem
   • CRoot cortex
   • DEpidermis

   (b)

   While it relies entirely on the mother plant for sucrose and amino acids, is the young plantlet acting as a source or a sink?

   [1 mark]

   • AA source
   • BNeither a source nor a sink
   • CBoth a source and a sink equally
   • DA sink

   (c)

   Explain what is meant by translocation, and explain why the young plantlet needs to receive sucrose and amino acids from the mother plant before its own leaves are photosynthesising.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A gardener takes several leafy cuttings from a shrub and places them under a clear plastic propagation dome that keeps the air around them constantly humid, rather than leaving them exposed to the drier air of the greenhouse, while they grow new roots.

   (a)

   What effect does increasing the humidity of the air around a leafy cutting mainly have on its rate of transpiration?

   [1 mark]

   • AIt increases the rate of transpiration
   • BIt decreases the rate of transpiration
   • CIt has no effect on the rate of transpiration
   • DIt stops photosynthesis completely

   (b)

   Why does higher air humidity have this effect on the rate of transpiration?

   [1 mark]

   • AIt reduces the concentration gradient of water vapour between the leaf's air spaces and the surrounding air
   • BIt permanently closes all the stomata
   • CIt increases the temperature of the leaf
   • DIt increases the wind speed around the leaf

   (c)

   Explain why keeping a leafy cutting under a humid propagation dome, before it has grown its own roots, improves its chances of survival.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Plant breeders compare two varieties of wheat seedling grown in identical dry soil: variety P, whose roots have unusually long, densely packed root hairs, and variety Q, a standard variety with shorter, more sparsely distributed root hairs. Variety P was found to take up water from the dry soil considerably faster than variety Q.

   (a)

   Explain, in terms of surface area, why variety P's root hairs allow it to take up water faster than variety Q's from the same dry soil.

   [3 marks]

   (b)

   Describe the route water then takes from a root hair cell of variety P through the plant to reach a leaf, and explain how variety P's faster water uptake could help it cope better with dry conditions than variety Q.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A revision class studies two related aspects of transport in plants: how the same storage organ, a daffodil bulb, can act as a source at one time of year and a sink at another, and how movement through xylem differs from movement through phloem in general. In late spring, after flowering, the daffodils' leaves continue photosynthesising for several weeks before dying back, while the bulb underground swells with a store of sugars that remains dormant over summer and winter; the following spring, before any new leaves have grown, the same bulb produces a new flower stalk and leaves using this stored food.

   (a)

   Explain why the daffodil bulb acts as a sink in late spring, when the leaves are still photosynthesising, but acts as a source the following spring, before new leaves have grown, using the terms source and sink in your answer.

   [6 marks]

   (b)

   Now compare the movement of substances through xylem with the movement of substances through phloem in general, referring to what is transported, the direction of movement, and the source of energy for movement in each case.

   [6 marks]

   Total for question 8: 12 marks

End of questions