Monday, August 13, 2007

Transport of materials in plants

TRANSPORT OF FOOD AND OTHER SUBSTANCES IN PLANTS




1.Leaves make food by the process pf photosynthesis. The food made by leaves is in the form of simple sugar (glucose). Other types of substances are called plant hormones are released from the tips of roots and shoots. Now every part of the plant needs food and other substances. So these substances are to be transported to all the parts of the plants like roots, stems, growing

regions etc. The movement of food from leaves to other parts of the plant is called Trans location. In plants, phloem Trans locates the food and other substances.

2.Phloem consists of sieve tubes and companion cells. Sieve tubes are living cells which contain cytoplasm but do not have nucleus. So its function is supported by companion cell. Each sieve tube has a companion cell next to it.

3.Food is prepared in the Mesophyll cells of a leaf. Food is trans located in the form of sucrose. The movement of water and dissolved minerals in xylem is always upward (from soil to leaves). The movement of food can be upward as well as down ward depending upon the needs of the plants.




The mechanism of transport of food in a plant.:-




1.The movement of food in the phloem takes place by utilizing energy. The areas where the nutrients are stored known as sink (e.g. root) and where they originate as source ( leaf). The movement of food is always from the source to the sink.

2.At source, leaves food is prepared in the form of glucose. Glucose is converted into sucrose. Sucrose enters into the phloem at the expense of energy from ATP.

3.The osmotic concentration of phloem will increase. Water now enters into sieve tubes by the ocess of osmoses due to which the hydrostatic pressure in the phloem tissue rises.

4.This high pressure produce in the phloem tissues allow the movement of food to all parts of the plants having low pressure in their tissues. At sink, sucrose move from the phloem into the storage site or growing parts of the plants. Water will also move out from phloem. Hydro static pressure will decrease in phloem at sink.




5.A pressure gradient is set up in the phloem with high pressure at source and low pressure at sink. So the phloem sap with food will move from source to the sink. The phloem transports food according to the need of the plant e.g., in spring even the sugar stored in the roots or stem tissue of a plant would be transported through phloem to the buds which need energy to grow.

Transport of water in plants

Plants need raw materials like CO2, water and minerals for photosynthesis and for various other purposes such as making of proteins. For plants soil is the richest source of water and minerals. Roots absorb these substances and transport to the various parts of the plant. The water and minerals dissolved in it move through special tissue present in plants called xylem. Xylem consists of two kinds of elements called tracheids and vessels. Vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water conducting channels reaching all parts of the plant.

1. The cells of root actively take up ions from the soil. This creates a difference in the concentration of these ions between the root and soil. Inside the root the concentration of ions is more than the soil. Cell of the root is hypertonic in nature. So water moves cosmetically into the root from the soil. Water reaches then to the xylem this result in hydrostatic pressure in the xylem. This pressure is known as root pressure that forces the water up in the plant.

2. However, this pressure is not enough to move water in tall plants. To move water in tall plants, plants use another process known as transpiration pull.





3. According to transpiration pull, water is lost in the form of water vapours through the stomata. Stomata take water from the deeper cells. Finally the water is taken from the xylem vessels of the leaf.


4. The water is in the xylem behaves like a solid column because of strong force of attraction between water molecules.


5. The evaporation of water molecules from the cell of the leaf creates a suction which pulls water from the xylem cells of root. The lose of water in the form of vapour from the aerial parts of the plant is known as transpiration.

SIGNIFICANCE OF TRANSPRATION

1 It helps in the absorption and upward movement of water and minerals from roots to the leaves.
2 It also helps in the temperature regulation. It protects the plant from heat injury.

How water is transported at night in plants.?

Ans:- During the day, when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem. During night, when stomata are closed, the transport of water is through root pressure.

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