Module 3 : Section 3 - Water Transport Flashcards
(30 cards)
How does water enter a plant
- Through the root hair cells
- passes the root cortex (including endodermis)
- then reaches the xylem
How is water drawn into the roots
Water is drawn into the roots via osmosis. Meaning it travels down a water potential gradient
How does water move
From areas of higher water potential to areas of lower water potential - goes down the water potential gradient
What is the water potential of roots
Generally roots have a high water potential
What is the water potential of leaves
- Leaves have a lower water potential than roots (because water constantly evaporated from them)
- creates a water potential gradient that keeps water moving through the plant in the right direction, from roots (high) to leaves (low)
What is osmosis
The diffusion of water molecules across a partially permeable membrane from an area of higher water potential to lower water potential
What are the pathways in which water can move into the xylem
- Symplast pathway
- Apoplast pathway
What is the Symplast pathway
- Goes through the living parts of the cell, the cytoplasm
- the cytoplasms of neighbouring cells connect through the plasmodesmata
- water moves through the Symplast pathway via osmosis
What is the Apoplast pathway
- goes through the non-living parts of the cell, cell walls
- the walls are very absorbent and water can simply diffuse through them as well as pass through the spaces between them
- the water carry solutes and move from areas of high hydrostatic pressure to areas of low hydrostatic pressure (along pressure gradient)
- this is an example of mass flow
What happens to the water in the Apoplast pathway when it gets to the endodermis
When the water in the Apoplast pathway gets to the endodermis cells in the root it’s path is blocked by a waxy strip called the Casparian strip
What does the Casparian strip force the water to do
It forces the water to take the Symplast pathway
Why is the capsarian strip forcing the water to take the Symplast pathway useful
- It is useful because it means the water has to go through a cell membrane. Cell membranes are partially permeable and are able to control whether or not substances in the through
- once past this barrier, the water moves into the xylem
What pathway is mainly used
- both pathways are used
- but the main one is the Apoplast pathway because it provides the least resistance
Xylem vessels transport….
Water all around the plant
How does the water leave the xylem into the cells at the leaves
Mainly by the Apoplast pathway
Water evaporates from the cell wall into…
The spaces between cells in the leaf
What are the stomata
Tiny pores in the surface of the leaf
What happens the the stomata open
Water diffuses out of the leaf (down water potential gradient) into the surrounding air
What is transpiration
The loss of water from a plants surface
Water moves up a plant against….
The force of gravity
What is the transpiration stream
The movement of water from the roots to leaves
What mechanisms move the water
- cohesion
- tension
- adhesion
What helps water move up the plant
Cohesion and tension
What is and how is tension created
- Tension is created when water evaporates from the leaves at the ‘top’ of the xylem
- tension (suction) which pulls more water into the leaf
