Exercise 2.2 Biology Questions And Answers
9.2.6
Explain how water moves from the soil to the leaves of a plant.
At first water enters the root by osmosis because the soil water has a lower solute concentration of minerals than the epidermal cell cytoplasm (there is a water potential gradient).
Water movement across the cortex cell is by two pathways both involving a water potential gradient. The cortex cell cytoplasm has a solute concentration gradient. This moves water symplastically from cell to cell by osmosis. The Apoplastic pathway moves water by capillary action of mass flow through the connecting cellulose cell wall.
The endodermis marks the beginning of the central stele of vascular tissue. Both minerals and water must pass through the plasma membrane of the endodermis. …show more content…
However, some plants live in very humid environments where evaporation rates may not be that great. Xylem vessels form a continuous pipe from the root up through the stem. along petioles to the leaf.
Xylem cells are produced from the division of the cambium and then differentiation into xylem
The cytoplasm full breaks down and the end wall break down to form the pipeline
To support the cell wall extra thickening take place. This often has characteristic patterns. Some spiral some annular (as here). This extra thickening resists the 'tension' created by the rate of evaporation Water molecules are attracted to each other by Cohesion. This action extends down the xylem creating a 'suction' effect.
There is also adhesion between water molecules and the xylem vessels
The cohesion and adhesion act together to maintain the water column all the way up from the root to the stomata.
The rapid loss of water from the leaf pulls the water column stressing the cohesion and adhesion between water molecules. The movement of water is an example of mass flow due to a negative pressure
Explain how water moves from the soil to the leaves of a plant.
At first water enters the root by osmosis because the soil water has a lower solute concentration of minerals than the epidermal cell cytoplasm (there is a water potential gradient).
Water movement across the cortex cell is by two pathways both involving a water potential gradient. The cortex cell cytoplasm has a solute concentration gradient. This moves water symplastically from cell to cell by osmosis. The Apoplastic pathway moves water by capillary action of mass flow through the connecting cellulose cell wall.
The endodermis marks the beginning of the central stele of vascular tissue. Both minerals and water must pass through the plasma membrane of the endodermis. …show more content…
However, some plants live in very humid environments where evaporation rates may not be that great. Xylem vessels form a continuous pipe from the root up through the stem. along petioles to the leaf.
Xylem cells are produced from the division of the cambium and then differentiation into xylem
The cytoplasm full breaks down and the end wall break down to form the pipeline
To support the cell wall extra thickening take place. This often has characteristic patterns. Some spiral some annular (as here). This extra thickening resists the 'tension' created by the rate of evaporation Water molecules are attracted to each other by Cohesion. This action extends down the xylem creating a 'suction' effect.
There is also adhesion between water molecules and the xylem vessels
The cohesion and adhesion act together to maintain the water column all the way up from the root to the stomata.
The rapid loss of water from the leaf pulls the water column stressing the cohesion and adhesion between water molecules. The movement of water is an example of mass flow due to a negative pressure