A xerophyte is a plant adapted to survive in conditions where water is scarce or difficult to obtain.

Give three xerophytic adaptations that reduce water loss from a leaf.

Stomata sunk into pits, a thick waxy cuticle, and leaves that are rolled or reduced to spines.

Explain how sunken stomata and leaf hairs reduce transpiration.

They trap a layer of humid air just outside the stomata, which reduces the water potential gradient between the leaf air spaces and the atmosphere, so water vapour diffuses out more slowly.

How does the stem of a cactus help it to survive drought?

The stem is swollen and fleshy so that it stores water, and it is green and carries out photosynthesis in place of the leaves, which are reduced to spines.

Why are cactus spines an adaptation to more than water loss alone?

They also deter herbivores, which would otherwise eat the plant for the water stored in its tissues.

OCR A-Level Biology B H422

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The Development of Species: Evolution and Classification

Plant adaptations and how they are investigated

3 things to know
Components 01, 02 and 03

Overview

Recall questions on xerophytes and how sunken stomata, leaf hairs and cactus stems reduce water loss, hydrophytes and aerenchyma, alpine, shade and sun plants, and investigating stomatal density with nail varnish impressions and leaf area against light intensity.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Define a hydrophyte and give one of its adaptations.

Key term

Describe an investigation to compare the stomatal density of two plant species from different habitats.

Key term

Define a xerophyte.

Questions from this subtopic

Each one with the model answer underneath.

1
Define a xerophyte.
Model answer
A xerophyte is a plant adapted to survive in conditions where water is scarce or difficult to obtain.
2
Give three xerophytic adaptations that reduce water loss from a leaf.
Model answer
Stomata sunk into pits, a thick waxy cuticle, and leaves that are rolled or reduced to spines.
3
Explain how sunken stomata and leaf hairs reduce transpiration.
Model answer
They trap a layer of humid air just outside the stomata, which reduces the water potential gradient between the leaf air spaces and the atmosphere, so water vapour diffuses out more slowly.
4
How does the stem of a cactus help it to survive drought?
Model answer
The stem is swollen and fleshy so that it stores water, and it is green and carries out photosynthesis in place of the leaves, which are reduced to spines.
5
Why are cactus spines an adaptation to more than water loss alone?
Model answer
They also deter herbivores, which would otherwise eat the plant for the water stored in its tissues.
6
Define a hydrophyte and give one of its adaptations.
Model answer
A hydrophyte is a plant adapted to living in water, and one adaptation is the presence of large air spaces called aerenchyma in the leaves and stems, which give buoyancy and carry oxygen to submerged tissues.

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The Developing Cell: Cell Division and Cell Differentiation

The Developing Individual: Meiosis, Growth and Development

The Development of Species: Evolution and Classification

Cells and Microscopy

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