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…
Water enters epidermal cell cytoplasm by osmosis. The solute concentration is lower than that of soil water due to the active transport of minerals from the soil water to the cytoplasm.
Apoplastic: water moves by capillarity through the cellulose cell walls. Hydrogen bonding maintains a cohesion between water molecules which also adhere to the cellulose fibres.
The endodermis is the outer tissue of the vascular root tissue. The casparian strip of the endodermis is a barrier to the movement of water of minerals by the apoplastic pathway. All solute and water must move through the plasma membrane of the endodermal cells before entering the stele.
The cellulose cell wall contains a strip (casparian strip) of a waxy water repellant substance called suberin.
The suberin prevents water and dissolved minerals from passing into the xylem by the apoplastic pathway.
Therefore water solution must pass through the plasma membrane of the endodermis. The endodermis plasma membrane can then selectively control mineral uptake and rate of uptake.
Minerals are actively loaded into the xylem which in turn causes water to enter the xylem vessel. Pressure within the xylem increases forcing water upward (Root Pressure). This is probably not a major factor in transpiration of large plants. To get the water into the xylem, minerals are actively loaded into the xylem which in turn causes water to enter the xylem vessel.
This creates a water potential gradient that moves water passively into the xylem.
Pressure within the xylem increases forcing water upward (Root Pressure). This is probably not a major factor in transpiration
Rather the pressure potential gradient (hydrostatic pressure) based on evaporation (tension) form the leaf is responsible for the upward movement of water in the xylem.
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
potential. Water movement through the leaf:
The heat raises the temperature of the leaf and water in the spongy mesophyll tissue is changed into water vapour.
With the stomatal pore open this gradient operates only over one cell thickness.
Water evaporates into the air
The water loss from the leaf draws new water vapour from the spongy mesophyll (symplastic & apoplastic movement) into stomatal air space.
In turn the water molecules of the mesophyll space draw water molecules from the end of the xylem
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…
Water enters epidermal cell cytoplasm by osmosis. The solute concentration is lower than that of soil water due to the active transport of minerals from the soil water to the cytoplasm.
Apoplastic: water moves by capillarity through the cellulose cell walls. Hydrogen bonding maintains a cohesion between water molecules which also adhere to the cellulose fibres.
The endodermis is the outer tissue of the vascular root tissue. The casparian strip of the endodermis is a barrier to the movement of water of minerals by the apoplastic pathway. All solute and water must move through the plasma membrane of the endodermal cells before entering the stele.
The cellulose cell wall contains a strip (casparian strip) of a waxy water repellant substance called suberin.
The suberin prevents water and dissolved minerals from passing into the xylem by the apoplastic pathway.
Therefore water solution must pass through the plasma membrane of the endodermis. The endodermis plasma membrane can then selectively control mineral uptake and rate of uptake.
Minerals are actively loaded into the xylem which in turn causes water to enter the xylem vessel. Pressure within the xylem increases forcing water upward (Root Pressure). This is probably not a major factor in transpiration of large plants. To get the water into the xylem, minerals are actively loaded into the xylem which in turn causes water to enter the xylem vessel.
This creates a water potential gradient that moves water passively into the xylem.
Pressure within the xylem increases forcing water upward (Root Pressure). This is probably not a major factor in transpiration
Rather the pressure potential gradient (hydrostatic pressure) based on evaporation (tension) form the leaf is responsible for the upward movement of water in the xylem.
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
potential. Water movement through the leaf:
The heat raises the temperature of the leaf and water in the spongy mesophyll tissue is changed into water vapour.
With the stomatal pore open this gradient operates only over one cell thickness.
Water evaporates into the air
The water loss from the leaf draws new water vapour from the spongy mesophyll (symplastic & apoplastic movement) into stomatal air space.
In turn the water molecules of the mesophyll space draw water molecules from the end of the xylem