Plant Adaptations to Water Availability
Xerophytes:
- Xerophytes are plants which are adapted to environments with a very little water availability.
- This can be plants the live in both hot and cold deserts.
- Thick waxy cuticle - this minimises water loss by diffusion directly though the cells at the top of the leaves
- Sunken stomata - pitted stomata minimises water loss as it reduces air movement over the stomata, creating a humid microclimate, reducing evaporation rate and the water potential gradient.
- Reduced number of stomata - minimised water loss by reducing places where water vapour can exit, but it also reduces the plants gas exchange abilities.
- Reduced number of leaves - minimises water loss by reducing SA:V ratio of plant, meaning there is less area for water to diffuse out.
- Hairy leaves - minimise water loss by reducing air flow and creating a humid microclimate which reduces evaporation rate and the water potential gradient.
- Curled leaves - minimises water loss within a microenvironment with no air flow creating a humid microclimate reducing evaporation rate and water potential gradient.
- Succulents - minimise water loss by storing water in parenchyma tissue in roots and leaves, giving a plentiful supply in times of drought.
- Leaf loss - minimises water loss by reducing SA:V during times of drought so there is less area for water to be lost from.
- Modified stems - minimises water loss by expanding to store water, which provides a plentiful supply during times of drought.
- Deep roots - roots can go deep into the ground to access water which is a long way below the surface.
- Shallow roots - a large network of roots just below the surface of the soil to collect any surface rainwater that falls.
- Dormancy - some plants lose leaves and stop working completely during times of drought, leaving seeds behind to rapidly germinate and grow when there is enough water.
- Storage organs - such as bulbs and tubers can store water below the surface, so there is a plentiful supply during times of drought.
- Dehydration and rehydration - some plants can withstand absolute water loss, appearing dead, then rehydrating when water is available. This is aided by the disaccharide trehalose which enables cells to survive drought unharmed.
- Wipe clear nail varnish on the underside of a leaf and let it dry.
- Place sellotape over nail varnish, and press down firmly.
- Peel off gently and place under a light microscope
- Count the number of stomata you can see in the area of the eyepiece, then multiply this by the size of the leaf.
- Hydrophytes are plants which are adapted to live in conditions where water is abundant, at the surface, submerged in or at the edge of bodies of water.
- No waxy cuticle - maximises water loss so plant does not become oversaturated, as transpiration is not an issue.
- Many stomata on the upper surface - maximising gaseous exchange and allowing water vapour to leave, particularly if the plant lives on the surface.
- Reduced structure - water supports the plant, so there is less requirement for mechanical strength
- Wide flat leaves - maximises SA:V to absorb as much light as possible, and to allow water loss as transpiration is not an issue.
- Small roots - water diffuses directly into stem, and plant is supported by water so roots are less important.
- Air Sacs - enable leaves to float at the surface where light intensity is strongest for most efficient photosynthesis.
- Aerenchyma - Specialised parenchyma tissue which aids buoyancy and forms an efficient pathway for oxygen into the tissues, important for the anoxic conditions.
- Pneumatophores - special aerial roots which grow directly into the air which have many lenticels, allowing entry of oxygen.