Plant adaptations to water availability 9.5 Flashcards
what are some adaptations than plants have to conserve water
- waxy cuticle reduces transpiration from leafs surface
- stomata found mainly on underside of leaf
^can be closed to prevent water loss
what are xerophytes
xerophytes are plants that are found in dry habitats where water availability is very low
conifers and marram grass are bath examples of xerophytes
xerophytes can be found in extreme cold as well where water is unavaiable as it is frozen
what are some adaptations found in many xerophytes to help with conserving water
- A thick waxy cuticle
- sunken stomata
- Reduced numbers of stomata
- reduced leaves
- hairy leaves
- curled leaves
- succulents
- leaf loss
- root adaptations
- avoiding the problem
How does a thick waxy cuticle help with water conservation
in most plants up to 10% of the water loss by transpiration is actually through the cuticle.
some plants have a particularly thick waxy cuticle to help minimise water loss.
This adaptation is common in evergreen plants and helps them survive both hot dry summers and cold winters when water can be hard to absorb from the frozen ground
How does a sunken stomata help to conserve water
many xerophytes have their stomata located in pits, which reduce air movement, producing a microclimate of still, humid (moist) air that reduces the water vapour potential gradient and so reduces transpiration.
These are seen clearly in xerophytes such as marram grass, cacti and conifers
how does a reduced number of stomata help to conserve water
Many xerophytes have reduced numbers of stomata, which reduce their water loss by transpiration but also reduce their has exchange capabilities
how does a reduced number of leaves help to conserve water
The leaves of conifers are reduced to thin needles.
These narrow leaves which are almost circular in cross-section have a greatly reduced SA:V ratio, minimising the water loss by transpiration
How do hairy leaves help to conserve water
some xerophytes have very hairy leaves that, like the spines of some cacti, create a microclimate of sill, humid air, reducing the water vapour potential gradient and minimising the loss of water by transpiration from the surface of the leaf.
Some plants - such as marram grass- even have micro hairs in the sunken stomatal pits
how do curled leaves help with to conserve water
- reduces water loss by transpiration
- confines stomata within a microenvironment of still, humid air to reduce diffusion of water vapour from stomata.
- found in marram grass
- How and why do succulent plants conserve water
- what is an example of a succulent plant
- store water in specialised parenchyma tissue in stems and roots
- water is stored when it is plentiful supply and then used in times of drought.
- desert cacti is an example
How does leaf loss help to conserve water
some plants prevent water loss through their leaves by simply losing their leaves when water is not available. Palo verde is a desert tree that loses all of its leaves in the long dry seasons. The trunk and branches turn green and photosynthesise with minimal water loss to keep it alive.
How do root adaptations help to conserve water in xerophytes
Many xerophytes have root adaptations that help them to get as much water as possible from the soil.
Long tap roots growing deep into the ground can penetrate several metres, so they can access water that is a long way below the surface.
A mass of widespread, shallow roots with a large surface area able to absorb any available water before a rain shower evaporates is another adaptations.
The root system of marram grass consists of vertical roots that penetrate metres into the sand.
They also have a mat of horizontal rhizomes (modified stems) from which many more roots develop to form an extensive network that helps to change their environment and enable the sand to hold more water.
what is an example of where plants have adapted to avoid the problem
- some plants adapt to cope with low water availability by losing their leaves and becoming dormant or dying and leaving seeds which then recover germinate once rains comes
which dissacharide helps to enable cells to survive unharmed even after being completely dehydrated
The ability to survive in this way is linked to the diassacharide trehalose, which appears to enable the cells to survive unharmed
what are hydrophytes
plants that live in water (submerged, on the surface or at the edges of bodies of water)
examples include water lilies and water cress which grow on the surface and duckweeds which are submerged
