unit 3, transpiration, cohesion and tension Flashcards
what is transpiration and where does it occur?
- the loss of water vapur from the stomata by evaporation
- occurs at the leaf due to the stomata being on the leaf
what are the 4 conditions that effect transpiration?
-light intenstiy
-temperature
- humidity
-wind
how does light intenstiy effect transpiration?
- positive correlation
-more light means the stomata are open wider - larger sufrace area for evaporation
how does temperature effect transpiration?
- positive correlation
- more kinetic energy so more molecules moving
-more evaporation
how does humidity effect transpiration?
- negative correlation
-more water vapour in the air compared to the leaf, so water potential more positive outside - reducing water potential gradient
how does wind effect transpiration?
- positive correlation
- more wind to blow away humidity
-maintaining water potential gradient
how does water move up the xylem, against gravity?
by: cohesion , adhesion and root pressure
what is cohesion?
- water molecules sticking together
-like molecules bonded together
how does cohesion happen?
- due to water being dipolar, o2- and h+, so hydrogen bonds form between water molecules and stick together
how does water move in the xylem?
a singular continuous column
what is adhesion?
-when water sticks to the walls of the xylem
- molecules sticking to unlike molecules
when is there bigger adhesion?
when the xylem is narrower
what is root pressure?
- water moves into the root by osmosis increasing the volume of liquid inside the root
- pressure increases in root
- this forces water upwards
what is capilarity?
upward motion against gravity
what increases capilarity?
when the xylem is narrower
what are features of the root hair cell?
- large surface area for maximal uptake of water
- creates a water potential gradient
- lots of mitochondira for active transport of minerals
what are the features of the xylem?
-elongated dead cells that are impermeable to water
-lignin strengthened walls that are waterproof
-dead cells, no cytoplasm or membrane make the transpiration more efficient
-continous tube no end plates
why is the strenghtneing of the xylem in spirals?
- to make the plant flexible so it doesnt snap
-less lignin which reduces the mass of the plant
-elongated
what do thick lignin walls prevent?
the xylem walls collapsing
describe the cohesion tension theory of water transport in the xylem
- water evaporates through leaf, creating a lower water potential in the mesophyll
- water is pulled up by cohesion, the water is a long continuous column due to the hydrogen bonds making them stick together
- there is adhesion of water to the walls of the xylem
- water is taken up through the roots
Explain how xylem tissue is adapted for its function
-long cells / tubes with no end walls;
continuous water columns;
-no cytoplasm / no organelles / named, made of dead cells
to impede / obstruct flow / allows easier water flow;
-thickening / lignin;
support / withstand tension / waterproof / keeps water in cells;
-pits in walls;
allow lateral movement / get round blocked vessels;
Describe and explain the effects of increasing light intensity on the tension in xylem vessels in leaves.
As light intensity is increased, tension in the xylem becomes greater.
> This causes the stomata to open more and increases the cohesion
> which increases the rate of transpiration
> Therefore the water potential of leaf cells become lower
> and more water moves out from xylem to surrounding cells down the water potential gradient.
