1. 1
   A botanist examines a cross-section of a dicotyledonous leaf and notes that the uppermost layer of cells beneath the outer waxy layer contains many densely packed chloroplasts, arranged in a single column of tall, closely fitting cells.

   (a)

   Which tissue is being described?

   [1 mark]

   • ASpongy mesophyll
   • BPalisade mesophyll
   • CLower epidermis
   • DVascular bundle

   (b)

   What is the name of the outer waxy layer that covers the upper surface of the leaf, reducing water loss?

   [1 mark]

   • AThe cuticle
   • BThe stomata
   • CThe phloem
   • DThe xylem

   (c)

   Explain how the position and structure of the palisade mesophyll layer adapts it for its function in photosynthesis.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Beneath the palisade layer, the botanist observes a layer of loosely arranged, irregularly shaped cells with large air spaces between them.

   (a)

   Which tissue is this, and which gas is most associated with moving through these air spaces?

   [1 mark]

   • AUpper epidermis; glucose
   • BPalisade mesophyll; water only
   • CSpongy mesophyll; carbon dioxide and oxygen
   • DVascular bundle; sucrose

   (b)

   Through which structures in the lower epidermis do gases enter and leave the leaf's internal air spaces?

   [1 mark]

   • ARoot hairs
   • BLenticels
   • CXylem vessels
   • DStomata, controlled by guard cells

   (c)

   Explain how the air spaces in the spongy mesophyll help to increase the rate of gas exchange within the leaf.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student examines a leaf cross-section and identifies a vascular bundle running through the centre of the leaf, containing both xylem and phloem tissue.

   (a)

   State the functions of the xylem and phloem found within this vascular bundle.

   [3 marks]

   (b)

   Most leaves, including the one examined by the student, have a large surface area and are thin. Explain how each of these two features is an adaptation for photosynthesis.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A biology class is given a complete diagram-free description of a dicotyledonous leaf cross-section, listing the cuticle, upper epidermis, palisade mesophyll, spongy mesophyll, guard cells and stomata, lower epidermis, air spaces and vascular bundles, and is asked to explain how the overall arrangement of these tissues adapts the leaf for efficient photosynthesis.

   (a)

   Explain how the arrangement of the upper tissues (cuticle, upper epidermis and palisade mesophyll) contributes to this efficiency.

   [6 marks]

   (b)

   Explain how the arrangement of the lower tissues (spongy mesophyll, air spaces, guard cells, stomata and vascular bundles) contributes to the leaf's overall efficiency at photosynthesis.

   [6 marks]

   Total for question 4: 12 marks

End of questions