science biology
Different methods of transpiration…
Water uptake from the soil:
Plant roots are surrounded by soil particles. The outmost layer of cells (the epidermis) contains root hair cells that increase the surface area of the root
These cells absorb minerals from the soil by active transport using ATP for energy
The minerals reduced the water potential of the cell cytoplasm; this makes the water potential in the cell lower than that in the soil.
Movement across a root:
The movement of water across the root is driven by an active process that occurs at the endodermis; this is a layer of cells surrounding the xylem, it is also known as the starch sheath as it contains granules of starch – a sign that energy is being used
The endodermis consists of special cells that have a waterproof strip on some of their walls – this strip is known as the Casparian strip
This strip blocks the apoplast pathway forcing water into the symplast pathway
The endodermis cells move minerals by active transport from the cortex into the xylem; this decreases the water potential in the xylem. As a result, the water moves from the cortex through the endodermal cells to the xylem by osmosis.
This reduces the water potential in the cells just outside the endodermis. This, combined with water entering the root hair cells, creates a water potential gradient across the whole cortex. Therefore water is moved along the symplast pathway from the root hair cells, across the cortex and into the xylem.
At the same time water moves through the apoplast pathway across the cortex. This water moves into the cells to join the symplast pathway before passing through the endodermis
The role of the Casparian strip:
It blocks the apoplast pathway between the cortex and xylem
Ensuring that water/nitrate ions pass into the cell cytoplasm through the cell membrane
Nitrate ions are actively transported from the cytoplasm of the cortex cells into the xylem
This lowers the water potential in the xylem so
Water uptake from the soil:
Plant roots are surrounded by soil particles. The outmost layer of cells (the epidermis) contains root hair cells that increase the surface area of the root
These cells absorb minerals from the soil by active transport using ATP for energy
The minerals reduced the water potential of the cell cytoplasm; this makes the water potential in the cell lower than that in the soil.
Movement across a root:
The movement of water across the root is driven by an active process that occurs at the endodermis; this is a layer of cells surrounding the xylem, it is also known as the starch sheath as it contains granules of starch – a sign that energy is being used
The endodermis consists of special cells that have a waterproof strip on some of their walls – this strip is known as the Casparian strip
This strip blocks the apoplast pathway forcing water into the symplast pathway
The endodermis cells move minerals by active transport from the cortex into the xylem; this decreases the water potential in the xylem. As a result, the water moves from the cortex through the endodermal cells to the xylem by osmosis.
This reduces the water potential in the cells just outside the endodermis. This, combined with water entering the root hair cells, creates a water potential gradient across the whole cortex. Therefore water is moved along the symplast pathway from the root hair cells, across the cortex and into the xylem.
At the same time water moves through the apoplast pathway across the cortex. This water moves into the cells to join the symplast pathway before passing through the endodermis
The role of the Casparian strip:
It blocks the apoplast pathway between the cortex and xylem
Ensuring that water/nitrate ions pass into the cell cytoplasm through the cell membrane
Nitrate ions are actively transported from the cytoplasm of the cortex cells into the xylem
This lowers the water potential in the xylem so