Transportation in Plants

Objective

This topic gives an overview of; 

  • Transport of Substances in Plants
  • Transport of water and minerals
  • Transpiration

Transport of Substances in Plants

You learnt that plants take water and mineral nutrients from the soil through the roots and transport it to the leaves. The leaves prepare food for the plant, using water and carbon dioxide during photosynthesis. You also learnt  that food is the source of energy and every cell of an organism gets energy by the breakdown of glucose. The cells use this energy to carry out vital activities of life. Therefore food must be made available to every cell of an organism. Have you ever wondered how water and nutrients absorbed by the root are transported to the leaves? How is the food prepared by the leaves carried to the parts which cannot make food?

Transport of water and minerals

Plants absorb water and minerals by the roots. The roots have root hair.The root hair increase the surface area of the root for the absorption of water and mineral nutrients dissolved in water. The root hair is in contact with the water present between the soil particles.Can you guess how water moves from the root to the leaves? What kind of transport system is present in plants?Plants have pipe-like vessels to transport water and nutrients from the soil. The vessels are made of special cells, forming the vascular tissue. A tissue is a group of cells that perform specialised function in an organism. The vascular tissue for the transport of water and nutrients in the plant is called the xylem.

The xylem forms a continuous network of channels that connects roots to the leaves through the stem and branches and thus transports water to the entire plant .

You know that leaves synthesise food. The food has to be transported to all parts of the plant. This is done by the vascular tissue called the phloem. Thus, xylem and phloem transport substances in plants.

Activity 

Take a large potato and peel off its outer skin. Cut one of its ends to make the base flat. Now make a deep and hollow cavity on the opposite side. Fill half of the cavity with sugar solution and mark the level by inserting a pin in the wall of the potato (Fig. 11.8). Put the potato into a dish containing a small amount of water. Make sure that the level of water is below the level of the pin. Allow the apparatus to stand for a few hours.You would find an increase in the level of sugar solution. How did water get inside the potato? For very short distances water can move from one cell to another. In the same way water reaches xylem vessels of the root from the soil.

Transpiration

In Class VI you learnt that plants release a lot of water by the process of transpiration.

Plants absorb mineral nutrients and water from the soil. Not all the water absorbed is utilised by the plant. The water evaporates through the stomata present on the surface of the leaves by the process of transpiration. The evaporation of water from leaves generates a suction pull (the same that you produce when you suck water through a straw) which can pull water to great heights in the tall trees. T ranspiration also cools the plant.

Summary

  • Birds, insects and lizard excrete uric acid in semi-solid form.
  • Water and mineral nutrients are absorbed by roots from the soil.
  • Nutrients are transported along with water to the entire plant via the vascular tissue called xylem.
  • The vascular tissue for the transport of food to the various parts of the plant is phloem.
  • A lot of water is lost by plants in the form of vapour through stomata during transpiration.
  • Transpiration generates a force which pulls up water absorbed by the roots from the soil, to reach the stem and leaves.
          

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