Transport In Plants Flashcards
The roles of water in a plant?
Maintaining cell turgidity for structure and growth
Transporting nutrients and organic compounds throughout the plant
Comprising much of the living protoplasm in the cells
Serving as a raw material for various chemical processes inc photosynthesis
Through transpiration, helping the plant cope with with temperature fluctuations
How is water absorbed in a root?
The water in the soil has solutes dissolved in it (mineral ions).
Their concentrations are much lower than the concentration of solutes inside the root hair cell.
The soil water therefore has a higher water potential than the inside of the cell.
This allows water to enter the root hair cell by osmosis
This water movement dilutes the contents of the cell, increasing its water potential
Water then moves out of the root hair cell into the outer tissue of the root (the root cortex)
Continuing in this way, a gradient of water potential is set up across the root cortex, kept going by water being taken up by the xylem in the middle of the root
How is water lost from a leaf?
Water leaves the cells of the leaf mesophyll cells
It evaporates into the air spaces between the spongy mesophyll cells
The water vapour then diffuses out through the stomatal pores
Which environmental factors affect transpiration?
Humidity
Wind speed
Temperature
Light intensity
How does humidity affect transpiration?
When the air around a plant is humid, this reduces the diffusion gradient between the airspaces in the leaf and the external air
The rate of transpiration therefore decreases in humid air and speeds up in dry air
How does wind speed affect transpiration?
The rate of transpiration increases with faster air movements across the surface of the leaf
The moving air removes any water vapour which might remain near the stomata
The moist air would otherwise reduce the diffusion gradient and slow down diffusion
How does temperature affect transpiration?
Higher temperatures increase the rate of transpiration by increasing the rate of evaporation of water from the mesophyll cells.
How does light intensity affect the rate of transpiration?
The rate of transpiration increases in the light because of the opening of the stomata in the leaves
How is a potometer used to measure water uptake by a shoot?
The whole apparatus is placed in a sink of water and any air in the tubing removed
A shoot is taken from a plant and the end of the stem cut at an angle
The shoot is put in under water and Vaseline is used to seal any joints
The movement of the water column in the capillary tube can be timed
If the water moves more quickly this shows a faster rate of transpiration
Describe the role of the phloem in transporting sucrose and amino acids between the leaves and other parts of the plant
The phloem supplies parts of the plant with the products of photosynthesis
So that tissues and organs that can’t make their own food receive products of photosynthesis
