Grade 7 | Science | Transportation in plants (water and food), Transportation in animals and plants, Olympiad, CBSE, ICSE, SOF, ITO
Transportation in plants
There are two main tissues which help in the transportation of food and water in the plants. These are narrow tube-like structures. Xylem is responsible for the transport of water, while phloem is responsible for the transport of food.
Transport of water
Water is absorbed from the soil by the roots with the help of root hairs in plants. Water enters the root hairs because of osmosis. As water enters the root hairs it enters further by the root pressure.
In stem, various factors play a key role in the transportation of water. The process of transportation through the xylem is called 'Ascent of sap'.
1. Capillary action pushes the water upwards as we know that in a very narrow tube liquid rise up by itself. This happens due to the very small diameter of the tube.
2. Adhesion Cohesion - This force comes into play when the water molecules stick to each other and make a continuous column inside the xylem tubes.
3. Transpirational pull- As we know leaves have small pores on its surface which are called stomata. When the water vaporizes from these pores during daytime (transpiration) then pressure builds up which we refer to as transportation pull. This provides a suction effect on the water column inside the xylem.
Xylem vessels are dead hollow tubes. These cell pathways are made from a substance called lignin which makes them waterproof. They also contain bordered pits. This allows water to move into them from the roots. They resemble the long drain pipes which are joined from end to end without any gap between them forming a long open tube.
Xylem vessels extend from the roots of a plant, passing through the stem and spread out in every leaf.
Xylem transports water and minerals from the roots, up to the leaves.
Transport of food
As we know leaf is the kitchen of the plant. The food made is needed to be transported in all the parts of the plant for use and storage. To facilitate the transport of food, the plants have phloem. It carries substances around the plant in a process called translocation. These are made from living cells, joined end to end, with punctured end plates to facilitate the flow of materials. Phloem tubes are bi-directional which means they can transport food in all the direction unlike xylem tissues.