transport in plants Flashcards
define transpiration
the process where evaporation of water from the leaves pulls a stream of water through the xylem vessels in the stem
explain how water is lost from a leaf
diffusion from an area of higher water vapour potential in an air space to an area of lower water vapour potential in the atmosphere through the stomata
explain how water is lost from mesophyll cells
evaporation from mesophyll cells into the air space
describe the two ways that water can replace that loss from mesophyll cells
movement of xylem through cytoplasm of cells by osmosis or movement from xylem through cell walls
define cohesion
attraction of water molecules to each other due to their polar nature, forming hydrogen bonds
define transpiration pull
the continuous column of water is pulled up the xylem due to transpiration
explain why there is a negative pressure in the xylem during transpiration
transpiration causing the movement of the water column puts the xylem under pressure
where does the energy needed for transpiration come from?
its a passive process but needs energy from the sun
where does the energy needed for transpiration come from?
it’s a passive process but needs energy from the sun
explain how water moves up the leaf
water evaporates from the cell walls of the mesophyll cells into the air spaces in the leaf. this lowers the water potential in mesophyll cells and water moves into them via osmosis from neighbouring cells.
the process is repeated through the cells.
replaced by water in the xylem
explain how water moves up the xylem
cohesion tension theory- water evaporates from the mesophyll cells, water molecules form hydrogen bonds between each other (cohesion). water forms a continuous, unbroken column through mesophyll cells and xylem creates a transpiration pull. this causes negative pressure in the xylem. its a passive process so no energy needed except light from the sun
