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Lesson 3 Parts of a Plant and their Functions We all know that plants are an important part of the living world. We also know that plants and animals are dependent on each other. There are many similarities between plants and animals, like: both need food, water and air to live; both have growth; both reproduce; both die. Animals have certain body systems which perform different functions. Plants also have systems. We have learnt about the functions of the human body. Let us find out the different parts of a plant and functions of each part. Look at the picture given below carefully. 26 What are the similarities among mango, sunflower, wheat and carrot plants? All have stems. All have leaves. The plants also have flowers and fruits. These are parts of the plant. There is another part of the plant which is usually under the ground and hence cannot be seen. This part is called the root. Each part of the plant has its own functions. Let us find out what are the different functions of each part of the plant. THE ROOT Roots absorb minerals and water from the soil. These are necessary for the growth of the plant. Roots help in holding the plant firmly on to the soil. Thus, roots also help in preventing blowing away soil from strong winds or flow of water. This is how plants help in holding the soil. Do you know that plants have two types of roots? One kind of roots grow vertically into the soil. These have many branches. This type of root is called taproot. The roots of sunflower, carrot and radish belong to this type of roots. The second type of roots are fibre-like which grow at the level of the ground and spread out in the soil. Such type of roots are called fibrous roots. Examples of such roots are wheat, maize, paddy, etc. 27 Write the names of any three plants which have taproot and three plants having fibrous roots. Plants with taproot Plants with fibrous root 1. __________________ 1. __________________ 2. __________________ 2. __________________ 3. __________________ 3. __________________ Some roots store food for the plant. Plants such as carrot and radish have this type of roots. We eat these roots as part of our food. Write the names of any three plants whose roots we eat. 1. ____________ 2. ____________ THE STEM Observe carefully the plant, given in this picture. The part of the plant above the soil which bears leaves, flowers and fruits is called the stem. You must have observe plants that have branches on their stems. 28 3. ____________ The stem bearing branches, leaves, flowers and fruits together make the shoot system of the plant. What is the function of the stem of a plant? Let us learn it by doing an activity. Let us take a plant which has a soft stem, e.g. balsam (gulmehndi) or vinca (sadabahar). Its stem should have leaves and flowers. Put this plant in a glass of water. Mix some red ink in the water. Observe the plant after two or three days. What difference do you observe in the plant? You will find some red stripes on the leaves and stem. (You can cut a part of the stem to confirm it.) Why does it happen? The stem carries water and minerals from the roots to different parts of the plant. The stem grows in the direction of light. We can understand this through an activity. 29 Take a potted plant. Put it in a cardboard box and close the box. Make a hole on one side of the cardboard box in such a way that light enters only through this hole. Take another potted plant and keep it in the open. Keep watering the plants regularly for a few days. > What do you find? You will find that the plant kept in the open, grow straight. The plant which was inside the box has bent towards the hole because it was getting light through this hole. Stems of some plants remain underground. Some of these stems also store food for the plant. These are called underground stems, e.g. potatoes, arbi, etc. Write the names of four plants which have underground stems and form part of our food. 1. _____________________________________________ 2. _____________________________________________ 3. _____________________________________________ 4. _____________________________________________ 30 THE LEAVES Leaves make food for the plant. There is a green pigment present in the leaves. It is called chlorophyll. Leaves of plants make food in the presence of sunlight with the help of chlorophyll. This process of making food by plants is called photosynthesis. Do leaves perform some other functions besides making food for the plant? Let us find out through an activity. Take two potted plants. In the first plant, apply some vaseline on both sides of the leaves and wrap it in a polythene bag (as shown on page 32). Wrap the other plant in a polythene bag without applying vaseline. 31 Keep both the plants in the sunlight. Observe the plants after four to five hours. Do you find any difference in the two plants? Yes! 1. No drops of water are visible in the polythene bag and on the leaves on which vaseline was applied. 2. There are drops of water in the polythene bag and on the leaves on which vaseline was not applied. Why have drops of water appeared on the leaves? The Surface of the leaves have small pores called stomata . Water vapour has come out from the stomata and collected on the leaves without vaseline. Water drops are also found on the inner side of the polythene covering this plant. 32 stomata In the other plant, the stomata are blocked due to the application of vaseline on the surface. Therefore, water vapours could not come out of the leaves through the stomata. Plants give out the excess water through these stomata. Stomata also help the plants by giving out oxygen and taking in carbon dioxide from the environment for making food. THE FLOWER AND THE FRUIT Flowers help plants in the process of reproduction. Fruit is formed from the flower after the process of reproduction. We eat fruits of many plants. Write the names of the other parts of a plant that we eat, besides the fruit. __________________________________________________ __________________________________________________ We eat a variety of fruits. Most of these fruits have seeds inside them. Some fruits have only one seed, like mango, jamun, etc. Some fruits have many small seeds, like Pomegranate, guava, orange, etc. Seed is a very important part of the plant. A new plant grows from the seed. The seed has a cover around it. This is called the seed coat. 33 After germination of the seed, the root and the stem of the plant come out. To understand the structure of a seed, break open a soaked gram and look carefully. You will find two soft structures joined together inside the seed coat. These are called cotyledons. The function of the cotyledon is to provide food to the young plant. Are cotyledons of all seeds alike? There are some plants which have one cotyledon in seeds while others have two. Let us find out through an activity. Get some seeds of gram, peas and maize. Soak them in water for a few days. Remove their seed coats and observe. What do you find? There are two cotyledons in grams and peas seeds. The maize and wheat seeds have only one cotyledon. THERE ARE DIFFERENT TYPES OF PLANTS There are certain plants which have a life span of one season. These plants are called annual plants, e.g., wheat, gram, mustard, paddy, etc. 34 Plants whose life cycle requires two seasons for complete growth are called biennial plants, e.g., carrot, sugarcane, etc. Some plants which have a life span of many years are called perennial plants. Mango, neem, lemon, etc., are some of the perennial plants. You must have seen that there are some plants which are small and soft. They are called herbs, e.g., wheat, spinach, fenugreek plants, etc. 35 Some plants have very weak stems. Hence they need support. Such plants grow along the ground. These are called creepers, e.g., pumpkin, gourd, grapes, etc. Some plants have very hard stems. In such plants, branches may arise from the lower part of the stem, e.g. Karonda, henna, etc. These plants are called shrubs. Some plants have tall, strong and woody stems. These are called trees, e.g., mango, peepal, pine, deodar, etc. 36 In this lesson We Have Learnt The root absorbs water and minerals for the plant from the soil. The stem carries water and minerals to all parts of the plant. It supports the plant. The leaves of the plant make food. Leaves take in carbon dioxide from the air and give out oxygen. Leaves also give out water vapour. Flower is the reproductive part of a plant. What Have We Learnt ? I. ORAL WORK 1. Tell four similarities between plants and animals. 2. Which part of a plant do you find most beautiful and why? 3. Name three fruits which have only one seed. 4. What are the differences between the functions of a root and a stem? 5. Name some plants in your neighbourhood whose flowers you find beautiful. II. WRITTEN 1. What is the difference between trees and creepers? 2. Write one function of each part of a plant. 3. What is the difference between taproot and fibrous root? 4. What is the difference between annual, biennial and perennial plants? Give one example of each of these plants. 37 5. Write the difference between shrubs and herbs. 6. Fill in the blanks: (a) The seed lies in the _______________ of a plant. (b) The shoot system is the _______________ part of the plant. (c) The stem of a tree is ______________ than that of a shrub. (d) The stem of a shrub is ____________ than that of a herb. III. THINGS TO DO • Visit a nearby garden and observe different kinds of plants there. List the names of three plants each of shrubs, trees and herbs. • Draw a picture on a chart paper of different parts of a plant and display it at home. • Find the names of any five plants which have thorns. • Find out which parts of plants are eaten by animals. 38