1. 1
   A biology class is examining a thin cross-section of a leaf under a microscope. Moving from the top surface downwards, they identify a single layer of covering cells, then a layer of tightly packed, column-shaped cells containing many chloroplasts, then a layer of loosely arranged, irregularly shaped cells with large air spaces between them, and finally a lower covering layer containing small pores.

   (a)

   Which plant tissue carries out photosynthesis and is found near the upper surface of a leaf?

   [1 mark]

   • AEpidermal tissue
   • BPalisade mesophyll
   • CSpongy mesophyll
   • DXylem

   (b)

   What is the main function of the loosely arranged tissue with large air spaces seen lower down in the leaf section?

   [1 mark]

   • ATo absorb the most light for photosynthesis
   • BTo transport sugars away from the leaf
   • CTo allow diffusion of gases within the leaf
   • DTo transport water into the leaf

   (c)

   Name the tissue that forms the covering layers at the top and bottom of the leaf, and state one function of this tissue.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gardener cuts across the stem of a young dicotyledonous plant and examines it under a hand lens. Near the centre of the cross-section she sees a ring of tissue made of thick-walled tubes, and just outside this ring she sees a second ring of tissue made of thinner-walled living cells arranged in tubes with connecting end walls.

   (a)

   Which plant tissue is responsible for transporting water and mineral ions from the roots upwards through the stem?

   [1 mark]

   • APhloem
   • BEpidermal tissue
   • CPalisade mesophyll
   • DXylem

   (b)

   What substance is mainly transported by the tissue found just outside the ring of thick-walled tubes in the stem?

   [1 mark]

   • ADissolved sugars
   • BWater and mineral ions
   • COxygen gas
   • DCarbon dioxide gas

   (c)

   State the name of the process by which dissolved sugars are transported around the plant, and name the tissue that carries out this process.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student examines cross-sections of a primary root and a primary stem from the same dicotyledonous plant. In the root, the xylem forms a central, star-shaped core with phloem located between the points of the star. In the stem, xylem and phloem are found together in separate vascular bundles arranged in a ring near the outer edge of the stem, close to the epidermis.

   (a)

   A student compares the internal structure of a primary root and a primary stem in a dicotyledonous plant. In the root, the xylem is arranged in a central, star-shaped core, with phloem located between its points. In the stem, the xylem and phloem are instead arranged together in separate bundles positioned around the outer edge of the cross-section, near the epidermis. Suggest one advantage to the plant of the xylem being positioned centrally in the root.

   [3 marks]

   (b)

   Suggest one advantage to the plant of the xylem and phloem being positioned near the outer edge of the stem, rather than centrally.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A farmer notices that a row of wheat plants growing in an area of compacted, waterlogged soil are wilting and showing poor growth, despite there being plenty of water present in the surrounding soil. Neighbouring plants growing in normal, well-aerated soil nearby look healthy.

   (a)

   A farmer notices that a row of wheat plants growing in compacted, waterlogged soil are wilting and show poor growth, even though there is plenty of water in the soil. Using your knowledge of plant tissues and organs, explain how damage to the root tissues in compacted soil could lead to wilting of the leaves, describing the roles of the tissues involved from the root to the leaf.

   [6 marks]

   (b)

   The farmer wants to test whether soil compaction is really the cause of the wilting, rather than another factor such as disease. Describe a suitable investigation she could carry out to test this, including how she would make the comparison fair.

   [6 marks]

   Total for question 4: 12 marks

End of questions