transport of water in plants Flashcards
What is transpiration?
The loss of water vapour from the stem and leaves of a plant as a result of evaporation.
How does movement of the water through the roots occur?
- Mineral ions enter the root hair cell via active transport.
- This causes the cell to have a lower water potential than the soil.
- Water moves from a high water potential in the soil to a low water potential in the root hair down a water potential gradient by osmosis.
Explain apoplast pathway.
1) water molecules are pulled along by cohesive forces, which pulls all water molecules along cell wall.
2) Waterproof Casparian strips in endodermal cells prevent movement of water across the cell wall, so water will move through cytoplasm for a short while.
3) Water is forced into the endodermal cells.
4) Mineral ions are actively transported from the endodermal cells into the xylem vessel.
5)Xylem water potential decreases.
6) Higher water potential in endodermal cells.
7) Water moves into xylem by osmosis.
Explain symplast pathway.
1) Water moves through the cytoplasm of cells by osmosis.
2) Root hair cell has a higher water potential than the first cell in the cortex.
3) Water moves from the root hair cell to the first cell of the cortex by osmosis.
4) The water potential of the first cortex cell increases so it is now higher than the second one. So water will move by osmosis from the first cortex cell to the second cortex cell.
5)This will continue across all cells of the cortex.
6) The water potential behind is lowered as a result of water moving out of these cells. Water will continue to move into the cells from the soil increasing their water potential.
Explain how water enters a plant root from the soil and travels through to the endodermis.
Water enters root hair cells by osmosis because active uptake of mineral ions has created a water potential gradient. Water moves through the cortex by osmosis down a water potential gradient through cell vacuoles and cytoplasm/ symplastic pathway through cell walls/ apoplastic pathway.
Explain how the structure of the endodermis affects the passage of water by the apoplstic pathway.
Casparian strips which are impermeable.
There is a lower water potential in the cytoplasm of the endodermis cell. Water enters symplastic pathway / cytoplasm of cell by osmosis.
How are root hair cells adapted to take up water from surrounding soil?
- Long and narrow, which increases surface area to volume ratio.
- Able to penetrate between soil particles.
- Able to maintain a water potential gradient between the soil and the cell, due to solutes dissolved in the root.
