9.5 Flashcards
What are xerophytes?
Plants living where there is short water supply, we need adaptations to enable plants to survive and reproduce.
Many plants live in dry habitats where water evaporates from leaf surfaces very rapidly.
Plants living in cold and icy conditions are also xerophytes as the water in the ground is not freely available to them because its frozen.
Xerophytes aim to conserve water.
How do xerophtes conserve water?
Thick waxy cuticle- minimise water loss by evaporation like cacti and marram grass
Sunken stomata- stomata located in pits reduce air movement producing a microclimate of still, humid, moist air which reduces the water potential gradient so therefore reduces transpiration.
Reduced number of stomata- many xerophytes have a reduced number of stomata which reduces water loss by transpiration by reducing their gas exchange capabilities.
What are the adaptations of leaves in xerophytes?
Spines- xerophytes like cacti have spines instead of leaves which reduce surface area for water loss by transpiration
Hairy leaves- some xerophytes have hairy leaves which trap water vapour near the surface of stomata hence reduces the water vapour potential gradient and minimises water loss by transpiration.
Curled leaves- reduces air flow near the surface of leaves which helps trap water vapour near the surface of the stomata which reduces the water vapour potential gradient and minimises water loss by transpiration. (E.g marram grass)
What are other adpatations of xerophytes?
- succulents store water in plentiful supply in specialised parenchyma tissue
Leaf loss- no water loss as transpiration cannot happen
Root adaptations- long roots which can penetrate water deep underground and also widespread shallow roots with a large surface area to absorb available water after a rain shower.
Dormant
What are hydrophytes?
Not all plants need to conserve water. Hydrophyes live in water need specialised adaptations to cope with growibng in water or permenantly saturated soil.
E.g water lillies live near the surface of leaves in order to capture as much light as possible for photosynthesis.
What is a major problem for hydrophytes?
Water logging- air spaces of a plant need to be full of AIR not water in order to survive
What are the adaptations of hydrophytes?
Thin or non waxy cuticle- hydrophtes do not need to conserve water so water loss by transpiration is not an issue
Open stomata on upper surfaces- maximising stomata maximises gaseous exchange.
Reduced structure to the plant- water supports leaves and flowers so no need for strong supporting structures.
What are the adaptations of hydrophytes?
Wide, flat leaves spread across the surface of water to capture as much light as possible.
Small roots- water diffuses directly into stem and leaf tissue so there is less need for uptake by roots.
Large SA of stems and roots under water- maximises area for photosynthesis and oxygen to diffuse into submerged plants
Air sacs- enables leaves and flowers to float to the surface of the water to get the light need for photosynthesis.
What is aerenchyma?
- makes leaves and stem more buoyant
- forms low resistance internal pathway for themovement of substances like oxygen to tissues below water (copes with anoxic- extremely low oxygen conditions)
