Transport in plants Flashcards
Function of xylem is to
transport water and mineral ions and provide support.
Function of phloem is to
transport sucrose and amino acid
Xylem have:
thick walls with lignin
no cell contents
cells joined end to end with no cross walls to form a long continuous tube.
The large surface area of root hairs increases
the uptake of water and mineral ions.
Pathway of water from soil:
root hair cells, root cortex cells, xylem, mesophyll cells.
Transpiration is the
loss of water vapour from leaves.
Water evaporates from the surfaces of the
mesophyll cells into the air spaces and then diffuses out of the leaves through the stomata as water vapor
Water vapour evaporates from the surface
of the mesophyll cell out of the leaf. This
reduces the pressure in the vessels. The pressure of the at the top of the Xylem Vessel is therefore less than the pressure at the bottom in the roots. Due to this pressure difference, water flows upwards. It is called transpiration pull. Because it is caused by loss of water vapour by transpiration.
At higher temperature rate of transpiration increases because
at a higher temperature,Molecules have greater kinetic energy, which means the rate of evaporation is higher from the surface of the mass of cells.
On a windy day, the air around the leaf – which contains a lot of water vapour that
has just diffused out of the leaf – is quickly moved away
This means that there is
always a diffusion gradient for the water vapour, because there is less of it outsidethe leaf than in the air spaces inside the leaf. So, water vapour
diffuses out of the leaf faster on a windy day than on a day when the air is still.
As humidity increase
rate of transpiration decrease because there is a smaller
diffusion gradient for the water between the air and inside leaf.
Cells loose water by
transpiration down the water potential gradient by osmosis. The
pressure of water on the cell wall decreases. The turgor pressure decreases. The
leaf become soft and fluffy. This is called wilting.
Translocation
movement of sucrose and amino acids in phloem from sources to sinks.
Sinks
parts of plants that use or store sucrose or amino acids
Sources
parts of plants that release sucrose or amino acids.