Transportation in plants
Investigate, using a suitable stain, the pathway of water through the above- ground parts of a plant.
Cut the base, non-leafy end, of a fresh stalk of celery under water. Place the cut end into a beaker of water stained with red food dye. Leave the celery stalk in bright light at room temperature in a breeze. Note the red lines moving up the stalk and then along the veins of the leafy parts. Cut across the stalk and note the curve of red dots close to the outer edge. If a thin section is examined under the microscope it is the xylem which has been stained red in colour.
Describe how water vapour loss is related to cell surfaces, air spaces and stomata.
In general, plants must close their stomata in order to conserve water, usually during a period of drought. However, this prevents the release of oxygen which would become toxic if concentrated highly enough.
State the pathway taken by water through root, stem and leaf (root hair, root cortex cells, xylem, mesophyll cells).
There is a high water potential in the soil and not-so-high water potential in the root hair cell, as the root hair cell has a very concentrated cell-sap. Because of this, osmosis occurs and water and inorganic ions move from the soil to the root hair cells, down a concentration gradient. The inorganic ions and water travel to the xylem tube, which is responsible for traveling the products up to the leaves. The xylem vessel transports the water and inorganic ions (minerals) up the xylem tube from the root to stem through a process called Capillary Action , against gravity. The water and inorganic ions leave the xylem and is absorbed by the cells in the leaves.
Explain the mechanism of water uptake and movement in terms of transpiration producing a tension ('pull') from above, creating a water potential gradient in the xylem, drawing cohesive water molecules up the plant.
Water transport up the plant, requires something that will allow it to work against gravity. For example, in the xylem tube, he water is flowing upwards right, from the soil to the tube. In order to work against gravity, water travels via this process called Capillary Action, which allows liquids to flow liquids to flow through narrow spaces such as the xylem tube without the assistance of gravity.
State the functions of xylem and phloem.
Xylem vessels transport water and dissolved minerals from the root up to all the other parts of the plant. Phloem vessels transports food nutrients such as glucose from the leaves to other parts of the plant.
