9.3 Flashcards
what is transpiration?
the loss of water vapour from leaves
how does a waxy cuticle help leaves?
they are waterproof so prevent water loss
what happens at the stomata?
CO2 moves in
O2 and water move out
why do some stomata always remain open at night?
plants cannot photosynthesise at night so need oxygen for respiration
what is the transpiration stream?
the movement of water from the roots to the leaves
how does water move from the xylem to the leaves for transpiration?
water travels through the symplast and apoplast pathways into mesophyll cells
at the mesophyll cells, water diffuses out and leaves the cell which creates a low water potential
the xylem has a high water potential so water moves down the water potential gradient into mesophyll cells
what is the transpiration pull?
water is cohesive and adhesive meaning molecules stick to the xylem walls as well as eachother
when water is drawn up the xylem to replace the water lost from transpiration, water moves up the xylem as one continuous stream
what evidence is there for the cohesion-tension theory?
when transpiration is at it’s highest, the trunk shrinks due to the tension
when xylem vessel is broken, water does not leak out and instead air is drawn in
what is a problem with transpiration?
it will always happen as long as the plant needs to do gas exchange for photosynthesis and respiration
therefore a plant cannot control how much water it loses
which wall of the guard cell is more flexible?
outer wall
how is the stomata opened?
when conditions are favourable, guard cells pump in ions bt active transport
this decreases the water potential so water moves into guard cell
causes guard cell to become bean shape and stomata is open
what factors affect transpiration?
light
humidity
temperature
air movement
how does light affect transpiration?
more light causes more of the stomata to open so more water being lost by transpiration from the leaves so a greater rate of transpiration
how does humidity affect transpiration?
if the humidity is very high, the water potential gradient is reduced which means the rate of transpiration decreases
how does temperature affect transpiration?
increasing the temperature increases the kinetic energy meaning evaporation is faster
