Transpiration Flashcards
What is transpiration?
loss of water by evaporation from the aerial parts of a plant
How does water get to the mesophyll cells?
water enters the leaves in the xylem and passes by osmosis into the mesophyll cells
What happens to the water in the mesophyll cells?
water evaporates from the surface of the cells to form water vapour
What happens to the water vapour?
Spongy mesophyll cells have large air spaces where the water vapour can diffuse through, as the vapour collects here the water vapour potential rises
What happens when the water vapour potential inside the leaf is higher than outside?
Water mols will diffuse out of leaf, open stomata are easy way to leave, open during day for gas exchange
What 3 processes does transpiration involve?
osmosis from xylem to mesophyll cells, evaporation from surface of mesophyll cells into intercellular spaces, diffusion of water from intercellular spaces through stomata
What are the 5 ways that water movement up the stem is useful?
water needed in leaves for photosynthesis, needed for cells to grow/elongate, keeps cells turgid, carries useful minerals up plant, evaporation keeps plant cool
How is the rate of transpiration measured?
potometer, measures rate of water uptake by a cut shoot, 99% water lost is transpiration so reasonable estimate,
How must the potometer be set up? How is the rate calculated?
no air bubbles, water lost by the leaf is replaced by water in the capillary tube, movement of meniscus measured
How does number of leaves affect rate of water loss?
More leaves = larger SA, more vapour can be lost
How does number, size and position of stomata affect rate of water loss?
many, large stomata = vapour lost quicker, on lower surface = vapour lost slower
How does the presence of cuticle affect the rate of water loss?
A waxy cuticle reduces evaporation from the leaf surface
How does light affect the rate of water loss?
In light, stomata open so more vapour is lost
What are the 3 ways that a higher temperature affect the rate of water loss?
increase evaporation so water vapour potential in leaf rises, water mols more kinetic energy so diffusion through stomata increases, decrease water vapour potential of air so more rapid diffusion out of leaf
How does relative humidity affect the rate of water loss?
Higher humidity decrease rate of water loss due to smaller water vapour potential gradient between air in leaf and outside
