Chapter 6 life process class 10th

     Transportation in plants 

Plants require a number of substances such as nitrogen, phosphorus, iron, calcium, magnesium, etc. for building their bodies. These substances are present in soil and are required even by parts situated at the top of plants.

Transportation in plants is carried out by two complex tissues - xylem and phloem. 

Xylem transports water and minerals from root to the aerial parts while phloem transports prepared food from leaves to the other parts of the plant. 

1. Transport of water

Water with its dissolved inorganic mineral nutrients is called sap the upward transport of water from the root to the aerial parts of the plants like branches, leaves, flowers, etc. is known as ascent of sap.

The ascent of sap takes place through xylem, a complex tissue. Xylem vessels, xylem tracheids, xylem parenchyma and xylem fibres are the various elements of xylem. 

The ascent of sap takes place through xylem vessels and xylem tracheids in flowering plants.

The land plants absorb water and minerals through the roots. These are absorbed by a large number of unicellular, tubular, hair like extensions present on root. These extensions are known as root hairs.

The water and minerals absorbed by root hairs passes from cell to cell through root cortex, endodermis and finally reaches the root xylem by osmosis.

Water is drawn into the xylem with a pressure equalling the difference between the osmotic pressure of xylem sap and soil solution. This pressure developed in roots is called root pressure.

The leaves possess stomata on their surface. A lot of water from the mesophyll cells of leaves keeps on evaporating into the air through the stomata. This loss of water from the leaves of plant is called Transpiration.

2. Transport of food and other substances

The food made by leaves is in the form of simple sugar. Every part of the plant needs food. The food manufactured by the leaves is transported to all parts of the plant through phloem.

The transport of food from the part where it is formed, leaves to all the other parts of plants is called Translocation.

The translocation of food takes place in both the directions, upwards as well as downwards. Sieve tubes and companion cells of phloem take active part in translocation of food.

The phloem transports not only the photosynthesis products but also some other substances like hormones, amino acids, etc.

Hormones are produced in root and shoot tips. From here they are transported to other pa rts where they affect growth, flowering and various other processes. Amino acids and a number of other substances are transported to storage and growing organs.

In living plants, food is continuously synthesized in the mesophyll cells of leaves by the process of photosynthesis. The food thus prepared is transferred to the seive tube of phloem. This is done by utilising energy from ATP. Dur to the increase in concentration of food material in sieve tube, its osmotic pressure increases. As a consequence water from the xylem enters the sieve tube by osmosis.

In the cells which continuously remove or use food or sugar e.g. root cells, the concentration of food decreases. The food present in sieve tube is transferred to the sink utilising ATP. As a result, the osmotic pressure of sieve tube decreases and water now leaves the sieve tube by osmosis.