Adaptations Xerophytes, Transport - Biology - Lecture Slides, Slides for Biology. Aligarh Muslim University
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sanat26 January 2013

Adaptations Xerophytes, Transport - Biology - Lecture Slides, Slides for Biology. Aligarh Muslim University

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These are the lecture slides of Biology. Key important points are: Adaptations Xerophytes, Transport, Pattern of Mass Loss, Plant Adaptations to Habitats, Mesophytes, Halophytes, Plants Adapted to Freshwater Habitat, Lea...
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Aims of the session: • Take measurements of leaves + see if xerophytes have a different pattern of mass loss • Learn about the adaptations xerophytes have • See what type of question they can ask about xerophytes (and be able to answer it)

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Plant adaptations to habitats Plants in different habitats possess different adaptations:

Mesophytes: plants adapted to a habitat with adequate water

Xerophytes: plants adapted to a dry habitat Halophytes: plants adapted to a salty habitat Hydrophytes: plants adapted to a freshwater habitat

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Hydrophyte: Leaf undersurface of the tree fern. Extremely high number of stomata per unit in a species living in tropic cloud forests where is is very moist.

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XEROPHYTES

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•Stomata sunken in pits creates local humidity/decreases exposure to air currents; •Presence of hairs creates local humidity next to leaf/decreases exposure to air currents by reducing flow around stomata; •Thick waxy cuticle makes more waterproof impermeable to water;

Xerophytes possess some or all of these adaptations to prevent excessive water loss

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Xerophytes possess some or all of these adaptations to prevent excessive water loss cont.

•Stomata on inside of rolled leaf creates local humidity/decreases exposure to air currents because water vapour evaporates into air space rather than atmosphere e.g. British Marram grass •Fewer stomata decreases transpiration as this is where water is lost;

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Adaptation

How it works

Example

thick cuticle

stops uncontrolled evaporation through leaf cells

small leaf surface area

less surface area for evaporation

conifer needles, cactus spines

low stomata density

smaller surface area for diffusion

sunken stomata

maintains humid air around stomata

marram grass, cacti

stomatal hairs (trichores)

maintains humid air around stomata

marram grass, couch grass

rolled leaves

maintains humid air around stomata

marram grass,

extensive roots

maximise water uptake

cacti

Xerophyte adaptations summary:

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Left and right Epidermis of the cactus Rhipsalis dissimilis. Left: View of the epidermis surface. The crater-shaped depressions with a guard cell each at their base can be seen. Right: X-section through the epidermis & underlying tissues. The guard cells are countersunk, the cuticle is thickened. These are classic xerophyte adaptations.

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Marram grass possesses: rolledleaves, leafhairs and sunkenstomata. These adaptations make it resistant to dry conditions and of course sand-dunes which drain very quickly retain very little water.

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