Water transport Flashcards
How and where does the water enter the plant?
Through the root into xylem
Water enters through the root hair cells and then passes through the root cortex, including the endodermis, to reach the xylem
Water is drawn into the roots via osmosis - travels down the water potential gradient.
- water always moves from high water potential to areas of low (down the gradient)
- The soil around the roots generally has a high water potential and leaves have low
- This creates a water potential gradient that keeps water moving through the plant in the right direction from roots (high) to leaves(Low)
How does the water move through the symplast way?
goes through the living parts (cytoplasm). The cytoplasm of neighbouring cells connect through plasmodesmata. Water moves through the symplast pathway via osmosis.
How does the water move through the apoplast way?
goes through the nonliving parts of the cells (the cell walls). The walls are v absorbent + water can simply diffuse through them, as well as pass through the spaces between them. The water can carry solutes and move from areas of high hydrostatic pressure to low (along the gradient).
What is the mass flow example?
- When water in the AW gets to the endodermis cells, its path is blocked by a waxy strip in the wall (casparian strip) now the water has to take the symplast pathway.
- Useful because it means the water has to go through the membrane. The membranes are partially permeable + able to control whether or not substances in the water get through
- Once past this barrier, the water moves into the xylem.
Which way is the main pathway?
Both ways are used but the main one is the AW because it provides the least resistance.
How does it go up the xylem and out the leaves?
Xylem vessels transport the water all around the plant
At the leaves, water leaves the xylem and moves into the cells mainly by the AW.
Water evaporates from walls into the spaces between cells in the leaf
When the stomata opens, the water diffuses out of the lead into the surrounding air.
The loss of water from a plant’s surface is called transpiration
How does water move up the plant against the force of gravity?
The movement of water from root to leaves - transpiration stream. The mechanisms that move the water include cohesion, tension and adhesion
Cohesion and tension help water move up plants from roots to leaves, against the force of gravity
Water evaporates from the leaves at the top of xylem (transpiration)
Created tension which pulls more water into leaf
Water molecules are cohesion so when some are pulled others follow. This means the whole column of water in the xylem from the leaves down to the roots, moves upwards.
Water enters the stream through the root cortex cells
How is adhesion responsible for the movement of water?
As well as being attracted to each other, water molecules are attracted to the walls of the xylem vessels.
This helps water to rise up through the xylem vessels.
