Transpiration :
Transpiration TRANSPIRATION is the evaporation of water from the leave of plants through the stomata TRANSIRATION STREAM is an unbroken column of water from the root, through the xylem, to the leaves, and then into the atmosphere.
Root pressure pushes water upwards due to the flow of water by osmosis.
Water is pulled up, as water evaporates from the leaves.
Transpiration pull is due to ADHESION and COHESION. The transpiration stream is important:
It provides transportation of water and minerals
Water is required for photosynthesis
Evaporation of water has a cooling effect on leaves.
Transpiration Stream :
Transpiration Stream by osmosis by osmosis and diffusion Osmosis It moves up xylem by transpiration pull Enters by Osmosis Moves into air spaces by evaporation Leaves by diffusion Factors affecting Transpiration rate:
INCREASES
High temperature
windy
dry
Stomatal Mechanisms :
Stomatal Mechanisms Photosynthesis occurs in the guard cells.
Guard cells absorb water from epidermal cell.
Turgid guard cells curve outward- opening. No photosynthesis occurs in guard cells.
Water lost to epidermal cells.
Flaccid guard cells straighten- closing.
Xerophytes :
Xerophytes XEROPYTES:
Live in dry, arid, or windy areas.
Have problems with
water shortages
High rate of water evaporation Sunken Stomata Thick cuticle Rolled leaf ADAPTIONS:
Thick waxy leaves & waxy coat is a barrier to diffusion which reduces evaporation.
Few leaves, needle leaves, few stomata reduces the surface area which reduces evaporation.
Reversed Stomata which makes the stomata closed during the day and open during the night this reduces evaporation.
Hairy leaves, rolled leaves, sunken stomata this traps the moist air around the stoma which reduces transpiration
Succulent tissue stores water which allows water to be available during a drought.
Superficial roots, long tap roots these increase the surface area of the roots which increases water uptake.
Hydrophytes :
Hydrophytes HYDROPHYTES:
live in water
Have problems with
Changing water levels
support Reduced xylem Large air spaces Stomata on upper surface Reduced cuticle ADAPTIONS:
Long leaf stalks that float on water makes sure leaves are always on the surface which allows gas exchange through Stoma.
Stomata on upper surface so that Stomata is in contact with the air which allows gas exchange through the stoma.
No cuticle on submerged leaf removes barriers to diffusion which allow gas exchange.
Air spaces in stem give the leaf buoyancy which holds the stem upright.
Xylem is reduced and in centre which makes the stem more flexile so it is less likely to be damaged