transpiration Flashcards
what is transpiration
the evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from the plant leaves, through the stomata
transpiration stream:
- the loss of water from the mesophyll cells sets up a water potential gradient
- this ‘draws’ water by osmosis from the surrounding mesophyll cells
- xylem vessels supply mesophyll tissues with water
- water enters root hair cell via osmosis
functions of the transpiration stream
- transporting mineral ions
- providing water to keep cells turgid to support the plant
- providing water to leaf cells for photosynthesis
- keep the leaves cool by evaporation
- providing water for the cytoplasm
what is the function of root hair cells?
absorb minerals and water from the soil
why do root hair cells contain no chloroplasts?
no photosynthesis is needed
why do root hair cells have a semi-permeable membrane
it will allow water and mineral ions into the cell
what’s the ‘finger-like’ projection for
increases surface area for absorption of water and mineral ions
list and explain 4 adaptations of root hair cells:
- finger-like extensions
-> increases SA:vol
-> to absorb water + mineral salts at a faster rate - low water potential/concentration
-> allows osmosis and diffusion of nitrates to take place - large vacuole
-> to absorb as much water as it can hold - is a living cell
-> carries out respiration
-> this provides energy for active transport to take place when the concentration gradient is reversed
role of roots in transpiration:
- water moves into the root hair cells by osmosis
-> high to low water potential
-> root hair cells have a large surface area to maximise water absorption
-> thin walls, decreases the distance of the pathway - water moves into the root cortex cells by osmosis
- water then moves into the xylem by osmosis
how do the transpiration stream help keep the water potential low?
the water is constantly moving from the root hair cells to the xylem. also, the high concentration of solute keeps the water potential low in the cell
why do plants need a transport system
to move nutrients and water within the plant
what does the xylem transport
water and dissolved minerals from the roots to other parts of the plant
what does the phloem transport
sucrose and amino acids between the leaves and other parts of the plant
the xylem contains……..
dead cells arranged end-to-end forming continuous vessels
what does the xylem begin life as?
living cells
as the xylem cells develop:
- become elongated
- original cell walls become impregnated with lignin (made by the cytoplasm)
what happens when xylem cells mature?
they contain no cytoplasm - instead they have a hollow central space (lumen) for water to pass through
what does the xylem transport and where does it transport it to?
- water and mineral salts
- from the roots up the shoot to the leaves in the transpiration stream
what are two roles of lignin?
- to transport liquids throughout the plant
- reinforces the cell walls and keeps them from collapsing
what is adhesion of water molecules
attraction to the cell wall
what is cohesion of water molecules
attraction to each other
what is a potometer
a simple piece of apparatus, which measures the rate of transpiration or the rate of water uptake by the plant
potometer practical method:
- apparatus is placed in sink of water
- cut stem of plant underwater
- stem is pushed into rubber tubing under water to stop any air entering
- vaseline is used to seal any joints
- if the water moves quickly, faster rate of transpiration
does high temp increase or decrease rate of transpiration and why
- increase
- increased kinetic energy of water molecules -> molecules move faster
- evaporation/diffusion faster
does high humidity increase or decrease rate of transpiration and why
- decrease
- air around plant is already saturated with water
- decrease gradient
does high light intensity increase or decrease rate of transpiration and why
- increase
- stomata open to all carbon dioxide to enter for photosynthesis
does wind speed increase or decrease rate of transpiration and why
- increase
- removes water vapour from leaf
