Plants uptake of water and climate conditions as factor


Under the leaves of most plants, stomata are found which are left open in order to exchange gases taking up carbon dioxide as well as getting rid of oxygen. However, once the stomata is left open, water vapour is lost from the leaves. This process is called Transpiration and it activated the following process called Transpirational pull. When water vapour is lost at the tip of the Xylem, a negative pressure is induced in that area causing the water in the stem to flow upwards, which occurs smoothly thanks to the cohesive and adhesive characteristics of water molecules. Waters cohesive characteristic, comes from the water molecules being polar and this sticking together because of the dipole bonds leading to them being capable of moving upwards on long distances with ease. Adhesion is another characteristic of water molecules which is also due to their Polarity interacting with he hydrophilic parts of the Xylem vessels helping them flow better upwards.

Note to remember is that Transpiration is indeed crucial for several reasons. One bing to provide raw material for photosynthesis, transport minerals to leaved for synthesis of molecules and to cool the leaves in hot conditions.

Epidermal roots are all located around the roots of the plants to increase intake to surface area and so Transpirational pull helps sucking up eater from the roots to the Xylems. The uptake from the roots to the Xylem can occur either through Apoplast (through the cell walls of the epidermal cell to the root) or Symplast ( through the cytoplasm of epidermal cells to the Xylem).

However, if Casparian strip present (a band of Suberin waxy substance impermeable to water found in cell wall of the endodermis of plant roots) makes the water from the endodermis onwards to flow through the symplast pathway to reach the Xylem vessels. Endodermis is the inner layer of cells surrounding the core of the root and the vascular tissue.

Moving on to the minerals, considering the concentration of the minerals are higher in the root hairs than the soil, active transport is needed with protein pumps in the plasma membrane of the root hair cells to move minerals against the concentration gradient into the cytoplasm. Whilst minerals are absorbed, water is also absorbed by osmosis leading to the minerals being dissolved in water by the time they reach Xylem vessels.

Depending on climate, plants have through evolution managed to cope with low rain fall called Xerophytes or high salt levels called Halophytes. Xerophytes such as Marram Grass, have managed to adapt in low water conditions by:

  1. Reducing the size of their leaves as well as make stems and leaves succulent to store water.

  2. Stomata are instead few and located on the stem of the plant for low water vapour loss and the stomata is only open during the night because of the cool environment in order to lose as little water as possible.

  3. Leaf epidermal cells are coated with waxy cuticles to also reduce water loss.

  4. Their leaves roll up in order to increase humidity around the stomata to in turn have little loss of water vapour.

  5. Increased surface area uptake by the roots, covering more ground.

One of the points mentioned stomata being open only during night of which makes carbon dioxide more important to have stored. Cacti have a system called Carssulacean acid metabolism CAS which converts the carbon dioxide absorbed by the night to magic acid which can be used for cabin dioxide in the light independent reactions.

Halophytes have managed to adapt to their salty conditions by:

  1. Also reducing their leave size and have their water storage structures develop in the leaves.

  2. Have thick cuticles and epidermis and their stomata are sunk into pits.

  3. Some plants have systems for removing salt build up by for example, actively pumping excess sodium and chloride ions into the surrounding water and soil.

#Stomata #Yas #YasAsghari #Plant #Xylem #Biology

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