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What Xerophytes look like - A Level Biology

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For A Level Biology, Module 3 for OCR exam board. You need to be able to recognize xerophyte plants as part of the exam.

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The following factors affect the rate of transpiration:

The opening and closing of the stomata is controlled by the [ guard cells guard cells: specialised cells which control the opening and closing of stomata in a green plant's leaves] .

In light, guard cells take up water by osmosis and become turgid. Because their inner walls are rigid they are pulled apart, opening the pore. In darkness water is lost and the inner walls move together closing the pore.

Because of this, the transpiration rate is increased by an increase in light intensity. The rate of transpiration can be affected by several factors:

The opening and closing of the stomata by the guard cells (stomatal rhythm)- In light, guard cells take up water by osmosis and become turgid. Because their inner walls are rigid they are pulled apart, opening the pore. In darkness water is lost and the inner walls move together closing the pore.Because of this, the transpiration rate is increased by an increase in light intensity.

Plants which live in extreme environments have adaptations to control their transpiration rate.

Xerophytes live in deserts where water is scarce and evaporation is rapid, or in windy habitats where evaporation can also be rapid. Their typical features are:

deep roots to reach water far underground

shallow spreading roots to collect occasional rainfall

leaves reduced to spines with minimum surface area for transpiration

reduced number of stomata to reduce transpiration rate

rolled leaves, leaf hairs and stomata sunk in pits to trap moist air, increasing humidity and slowing diffusion of water vapour from the stomata

waxy leaf cuticle which is impermeable to water (preventing evaporation)

stomata opening at night and closed at midday when evaporation rate would be highest (reversed stomatal rhythm).

storage of water in succulent tissues

Example 1: Cactus

Example 2: Marram grass

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BBC - Higher Bitesize Biology - Maintaining water balance : Revision, Page4

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The following factors affect the rate of transpiration: The opening and closing of the stomata is controlled by the [ guard cells guard cells: specialised cells which control the opening and closing of stomata in a green plant's leaves] . In light, guard cells take up water by osmosis and become turgid.

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Revision:Xerophytes and Hydrophytes | The Student Room