1. 1
   A botanist examined a transverse section of a plant stem and identified two different transport tissues. One consisted of dead cells joined end to end with no cross walls and thickened lignified walls. The other consisted of living tubes with perforated end walls, each associated with a companion cell.

   (a)

   Which tissue consisted of dead cells joined end to end with no cross walls and thickened lignified walls?

   [1 mark]

   • AXylem
   • BPhloem
   • CPalisade mesophyll
   • DEpidermis

   (b)

   Which substances are mainly transported in the living tissue with sieve tubes and companion cells described by the botanist?

   [1 mark]

   • AStarch and cellulose
   • BWater and mineral ions
   • COxygen and carbon dioxide
   • DSucrose and amino acids

   (c)

   Explain how the structure of the dead, lignified tissue identified by the botanist is related to its function of transporting water and providing support.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gardener cut a complete ring of bark, including the phloem, from around the trunk of a tree without damaging the xylem underneath (ring barking). Several weeks later, swelling was seen in the bark just above the cut, and the roots began to show signs of starvation.

   (a)

   What is the most likely explanation?

   [1 mark]

   • AMineral ions from the soil build up above the cut because the xylem is blocked
   • BWater is unable to move up the xylem, so it accumulates above the cut
   • CSucrose made by the leaves accumulates above the cut because the phloem pathway to the roots has been broken
   • DOxygen absorbed by the leaves cannot reach the roots, so it builds up above the cut

   (b)

   Why do the roots eventually show signs of starvation after the tree has been ring barked in this way?

   [1 mark]

   • AThe xylem, which normally carries sucrose to the roots, has been removed
   • BThe phloem, which normally carries sucrose from the leaves (source) to the roots (sink), has been removed
   • CThe roots can no longer absorb water because the phloem has been removed
   • DThe roots can no longer photosynthesise because the phloem has been removed

   (c)

   Explain, in terms of sources and sinks, why sucrose builds up in the tissue just above the cut rather than passing further down the trunk.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student stood the cut base of a white flower stem in a beaker of blue dye. After several hours, thin coloured strands were visible running up the length of the stem, and a transverse section cut through the stem showed the dye concentrated in small discrete regions.

   (a)

   A student stained the base of a white flower stem by standing it in a beaker of blue dye. After several hours, thin coloured strands were visible running up the length of the stem. Explain what this investigation shows about the position and structure of xylem in the stem.

   [3 marks]

   (b)

   The student then cut a thin transverse section of the stained stem and viewed it under a microscope. Describe the appearance and position of the stained xylem tissue in the section, and explain one way this arrangement could be investigated further using a different plant organ.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A farmer noticed that a fungal disease had destroyed patches of phloem tissue in the lower stems of several crop plants, while leaving the xylem undamaged. The farmer was concerned about the effect on root growth and fruit development, even though the plants did not appear to be wilting.

   (a)

   Describe the structure and function of phloem tissue, and explain the effects that this damage is likely to have on the growth of the roots and developing fruit of the affected plants.

   [6 marks]

   (b)

   Suggest and explain why the farmer's crop plants did not wilt despite the phloem damage, and discuss what additional evidence the farmer could gather to confirm that the reduced fruit yield was caused specifically by phloem damage rather than by another factor such as water shortage.

   [6 marks]

   Total for question 4: 12 marks

End of questions