Edexcel IGCSE Biology 2.21 Mineral ions & plant growth

Practise using leaf cross-sections to explain how tissues and cells are positioned and adapted for photosynthesis and water control.

Exam points

use leaf diagrams to identify palisade mesophyll, spongy mesophyll, xylem and epidermis
explain how transparent epidermis, chloroplast-rich palisade cells and air spaces support photosynthesis
compare palisade and spongy mesophyll by position, packing, chloroplast number and gas spaces

[Maximum number: 6]

The diagram shows a section through a leaf with different parts labelled P to U .

Figure for Question 2.21 Leaf adaptations for photosynthesis question 1 — Edexcel IGCSE Biology

(a)

Which part absorbs the most sunlight?

[ 1 ]

(b)

Which part reduces the amount of water escaping?

[ 1 ]

(c)

Explain how the structure and position of cells in parts R and T help the leaf to photosynthesise.

[ 4 ]

An explanation that makes reference to four of the following points:

- R / palisade are near top / surface to absorb as much light as possible / eq

- R / palisade contain many / eq chloroplasts / lots of chlorophyll to absorb as much light as possible / eq

- R / palisade / are densely packed/ rectangular / long / arranged vertically to absorb as much light as possible / eq

- T / spongy are near bottom of leaf / stomata for absorption of $\mathrm{CO}_{2}$

- T / spongy are less densely packed / have air spaces/ gaps for diffusion / gas exchange / gas movement /eq

Adaptation and reason needed for each mark

Need only mention absorb light once

must indicate many / eq

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2.21 Leaf adaptations for photosynthesis question 1

Question (a)

Question (b)

Question (c)