Xylem and transpiration Flashcards
what are the functions of xylem vessels in plants
to transport water and dissolved minerals up the plant
strength and support
how is the xylem specialised for water transport
continuous hollow column
pits in the walls
lignin waterproofs the walls
cellulose and lignin in the walls
lignin is laid down in spirals or rings
xylem vessels have a wider diameter
how does the xylem being a continuous hollow column make it good at transporting water
made of dead cells with no end walls, no cytoplasm, no cell contents
has less resistance to movement of water up the plant
how does the xylem having pits in its walls make it good at transporting water
allows sideways movement of water (from one vessel to another)
how does the xylem having lignin waterproofing its walls make it good at transporting water
keeps water inside of the vessel (less water is lost)
how does the xylem having lignin and cellulose in its walls make it good at transporting water
provides strength and support to prevent vessels collapsing
how does the xylem having lignin laid down in rings or spirals in its walls make it good at transporting water
strength and support
how does the xylem having a wider diameter in its walls make it good at transporting water
allows transport of large volumes of water
what is transpiration
the loss of water vapour from the surface of the plant e.g. leaves
what is the process if water transport in a plant from the roots to the leaves
- water evaporates from the surface of the leaf cells into the air, leaving the plant by transpiration (water vapour diffusing out of the leaves through the stomata down a diffusion gradient)
- this creates a low hydrostatic pressure in the leaves, drawing water out of the xylem vessels by osmosis
- a continuous column of water molecules is pulled up the xylem by capillary action this is due to:
cohesion-hydrogen bonding between polar water molecules in xylem
adhesion-hydrogen bonding between water and cellulose in the xylem walls
-water moves into the roots by osmosis which creates a high hydrostatic pressure
-water moves along a hydrostatic pressure gradient from high to pressure in roots to low pressure in the leaves by mass flow
what is cohesion and what does it do in plants
the attraction between like molecules
hydrogen bonding results in strong cohesive forces that keep water together in a continuous column in the xylem
what is adhesion and what does it do in plants
the attraction between unlike molecules
hydrogen bonds between water molecules and the cell wall
what is capillary action in a leaf and what does it do
minute channels between cellulose microfibrils of cell walls and pores act as tiny capillaries
replaces water within the cell walls
how do capillaries have a tendency to draw up water
because of capillary action caused by surface tension
how is surface tension caused
by cohesive forces between water molecules causing the surface layer of water to contract
why is thermal energy from the sun a process that occurs during transpiration
thermal energy needs to heat the water in the leaf which forms water vapour which evaporates from the leaf cells into the substomatal cavity
how does water enter the root cells and what pressure does it create
by osmosis
creates high hydrostatic pressure
how does water move in a plant cell (pressure wise)
from high pressure (in the roots) to a low pressure into the leaves
down a pressure gradient
moves passively by mass flow
