Question 1 What is a tissue?
Question 2 What are vascular tissues? Name two types of vascular tissues present in plants?
Question 3 What are xylem and phloem? State the functions of xylem and phloem in plants?
Question 4 Define the term transpiration?
Question 5 How does movement of water in a plant differ from the movement of food in it?
Question 6 What are stomata?
Question 7 Give few functions of stomata?
Question 8 Why transpiration is important in plants?
Question 9 How do water and minerals move from the roots of a plant to the leaves?
Question 10 How does food move from leaves to all other parts of a plant?
Question 11 Why do plants need a transport system?
Transport in Plants
A tissue is a group of similar cells which work together to perform a particular function. The arrangement of cells in a tissue depends on the function to be performed by the tissue.
Those tissues which transport water, minerals and food to different parts of a plant, are called vascular tissues.
There are two types of vascular tissues in a plant: xylem and phloem
(1) The tissue which carries water and minerals from the roots to the leaves of a plant is called xylem.
(2) The tissue which carries food from the leaves to other parts of the plant is called phloem.
All the parts of a plant like roots, stems, branches and leaves contain vascular tissues called xylem and phloem.
The xylem and phloem tissues are a kind of tubes made of tubular cells arranged end to end.
The Xylem tissue is made of dead Xylem cells whereas phloem tissue is made of living phloem cells arranged one over the other.
The plants take up water (and dissolved minerals) from the soil through their roots and transport it to their leaves for the preparation of food. The leaves of plants prepare food by water brought in from soil and carbon dioxide taken from air during photosynthesis. And this food has to be transported from the leaves to all other parts of the plant (which cannot make food themselves)
Plants need a transport system
(1) to carry water (and dissolved minerals) absorbed by the roots up to the leaves.
(2) to carry the food made in the leaves to all the parts of the plant (including roots).
The transport system in plants consists of long tubes (or vessels) called xylem and phloem.
(1) The vascular tissue called xylem carries water (and minerals dissolved in it) from the roots upwards through the stem and branches up to the leaves . The xylem tissue forms continuous network of vessels (or channels) that connect the roots to the leaves through the stem and branches, and thus transports water (and dissolved minerals) to the leaves of the entire plant. In a plant, water evaporates continuously from the leaves through the pores called stomata. The continuous evaporation of water from the leaves (or transpiration) produces a suction force which pulls the water from roots upwards through the stem and branches up to the leaves.
(2) The vascular tissue called phloem carries the food from the leaves to all other parts of the plants(including roots). The phloem tissue forms a network of vessels (or channels) that connect the leaves to all the parts of the plant including roots, and thus transports food to the entire plant. The food which is made in the leaves during photosynthesis consists of glucose (sugar) and it is transported within the plant in the form of solution.The force needed to push the dissolved food (glucose solution) in phloem vessels is generated by the living phloem cells present in the phloem tissue of the plant.
The process of transpiration (evaporation of water from leaves) serves a very useful function in the plants because
1) it generates a suction force in xylem which can pull water from the roots up to great height in the tall trees.
2) It cools the plant in hot weather. The rate of transpiration increases in moving air. This is because moving air carries away water vapour from leaves as fast as it comes out of stomata. And when the rate of transpiration increases, then the rate of absorption of water through the roots also increases.
Stomata are the tiny pores found on the surface of leaves of plants. The opening and closing of the stomata controls the passage of gases and water vapour into and out of the leaf.
(1) Carbon dioxide gas enters in and oxygen gas ‘goes out’ through stomata during photosynthesis.
(2) Water vapour passes out through stomata during transpiration.
Water reaches from soil to Xylem vessels in roots
(1) Movement of Water From Soil to Root Hair
The roots have large number of root hair. The root hair are in contact with the water present between the soil particles. Water from the soil enters the root through root hair The large number of fine root hair increase the surface area of the root in contact with the soil water due to to which more water can be absorbed by the root at a rapid rate.
(2) Movement of Water From Root Hair to Xylem Vessel in Root
The root hair are on the outer surface of the root, xylem vessel is in the centre of the root, and there are many cells of the root in-between the root hair and xylem vessel. Water absorbed by the root hair from the soil moves from cell to cell in the root and ultimately enters the xylem vessel which is located in the centre of the root. Once the water reaches the xylem vessel of root, it moves upwards and goes into interconnected Xylem vessels of stem, branches and leaves of the plant.
Water (containing dissolved minerals) from the soil enters a plant through its root hair. From root hair, water moves from cell to cell in the root till it reaches xylem vessel in the centre of the root. From the xylem vessel in root, water moves upward to the xylem vessels in stem, branches and leaves.
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