Transport in plants- Plant adaptations to water availability Flashcards
What adaptations to most plants have to conserve water?
- waxy cuticle to reduce transpiration
- stomata is mainly found on the underside of the leaf and can close to prevent water loss.
what are xerophytes?
plants which have adapted to live in environments with little water availability. This can be cold or hot deserts.
give two common examples of xerophytes?
marram grass and cacti
how does a thick waxy cuticle in xerophytes conserve water?
minimises water loss by diffusion from stomata
how does sunken stomata in xerophytes conserve water?
sunken stomata in pits reduces air movement creating humid air which reduces the water potential gradient, reducing transpiration.
how does a reduced number of stomata in xerophytes conserve water?
reduces water loss by transpiration but also reduces gas exchange abilities
how does reduced leaves in xerophytes conserve water?
minimises water loss by reducing surface are to volume ratio meaning there is less area for water to diffuse out. Xerophytes can also lose their leaves in times of drought.
how do hairy leaves in xerophytes conserve water?
minimises water loss by reducing air flow and creating air which reduces evaporation rate and water potential gradient.
how does curled leaves in xerophytes help conserve water?
minimises water loss which confines stomata within a humid microenvironment minimising evaporation and the water potential gradient.
how do succulents in xerophytes help conserve water?
minimise water loss by storing water in the parenchyma tissue in the roots and leaves giving a plentiful supply in times of drought.
how do modified stem in xerophytes help conserve water?
minimises water loss by expanding to store water which provides plentiful supply in times of drought.
how do deep roots in xerophytes help conserve water?
roots can go deep into the ground to access water which is a long way below the surface
how do shallow roots in xerophytes help conserve water?
a large network of roots just below the surface of the soil to collect any rainwater that falls.
how does dormancy in xerophytes help conserve water?
some plants stop working in times of drought, leaving seeds behind to rapidly germinate when there is enough water
how do storage organs in xerophytes help conserve water?
bulbs and tubers can store water below the surface so there is plentiful supply in times of drought.
How does dehydration and rehydration in xerophytes help conserve water?
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 droughts unharmed
how do you measure stomatal numbers?
1) wipe clear nail varnish on the underside of a leaf and let it dry
2) place sellotape over nail varnish, and press down firmly
3) peel off gently and place under a light microscope
4) count the number of stomata you can see in the area of the eyepiece and multiply it by the size of the leaf
what is a hydrophyte (e.g water lilies)?
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
why is there no waxy cuticle in hydrophytes?
maximises water loss so plants don’t become oversaturated, as transpiration is not an issue.
why is water logging a major problem for hydrophytes?
excess water fills air spaces of the plant which is needed for gaseous exchange
why do hydrophytes have many many stomata on the upper surface?
maximises gaseous exchange and allows water vapour to leave
why do hydrophytes have a reduced structure?
it reduces the requirement for mechanical strength as the leaves and water support the plant.
why do hydrophytes have wide flat leaves?
maximises the surface area to volume ratio to absorb as much light as possible and to allow water loss
why do hydrophytes have small roots?
water can diffuse directly into the stem and leaf tissue so there is no need for uptake by roots
why do hydrophytes have air sacs?
they enable the leaves to float at the surface where light intensity is strongest for efficient photosynthesis
Why do hydrophytes have aerenchyma?
It is a specialised parenchyma tissue which aids buoyancy and forms an efficient pathway for oxygen into the tissues which are important in anoxic conditions
Why do hydrophytes have pneumatophores?
these are special aerial roots which grow directly into air which have many lenticels allowing entry of oxygen.
What is the problem about aerenchyma?
provides a low resistant pathway by which methane produced by rice plants can be vented into the atmosphere. Methane contributes to the greenhouse effect.
