1. GENERAL CHARACTERISTICS OF PLANTS
- Plants have roots that fix them in the soil. They mostly lie below the ground and absorb water and minerals from the soil.
- The stem grows above the ground and helps to carry water, minerals and food to all the parts of the plant.
- Branches bear leaves, flowers and fruits.
- Leaves help the plant to prepare food with the help of water, carbon dioxide in the presence of sunlight and chlorophyll.
- Many plants bear flowers that change into fruits.
- Fruits have seeds inside them. Some fruits are fleshy and sweet.
- Seeds give rise to new plants.
- Plants cannot move from one place to another on their own but show movements of their body parts.
- Plants breathe through stomata which are tiny pores present mostly on the lower surface of the Leaves.
- Plants either grow from seeds or from other parts of the plants.
2. PREPARATION AND STORAGE OF FOOD IN PLANTS
A plant prepares food not only for itself, but for the whole of the living world. All plants depend on their leaves to make food. Since, leaf is the place where food is prepared, it is called the kitchen or food factory of the plant.
Parts of a Leaf
The flat part of a leaf is called the leaf blade. Running through the middle of the leaf is the main vein called midrib. There are number of side veins coming out of the main vein.
The main vein and side veins have tiny tubes inside them. Some help to carry water and minerals to all parts of the leaf and others carry food prepared by the leaf to other parts of the plant.
The tip of the leaf is called the leaf apex. The leaf is attached to the stem by means of a stalk. The petiole is a stalk that connects the blade with the leaf base. Mostly the underside of the leaf has many small pores, called stomata (singular : stoma) which help the plant in exchange of gases during breathing and photosynthesis. We cannot see these pores with the naked eye.
The process by which green plants make their own food using carbon dioxide and water in the presence of sunlight is known as photosynthesis. ‘Photo’ means ‘light’ and ‘synthesis’ means combining. Leaves combine carbon dioxide from air and water from the soil in the presence of sunlight which is trapped by the green pigment chlorophyll present in the leaves.
|Photosynthesis in a plant|
Leaves is also called the Kitchen of Plants
The process of photosynthesis takes place in leaves. They require following materials carry out the process.
- Sunlight : As it falls on the leaves it to absorbed by chlorophyll.
- Water : Water and minerals are absorbed by the roots and carried by the stem to the leaves.
- Carbon dioxide : The tiny pores caller stomata on the under surface of the leaf take in carbon dioxide from the air Stomata also help to remove extra water.
The food is prepared in the form of glucose which is a kind of sugar. Oxygen is released during this process which is essential for the survival of all living beings,
|Carbon dioxide + Water||————>||Glucose + Oxygen|
The glucose so formed is taken to all parts of the plant by the stem. The plant uses this food for :
- getting energy
- producing more branches and leaves,
- making flowers, fruits and seeds,
- repairing damaged parts.
Extra glucose is stored in the form of starch in different parts of the plant like root, leaf, stem, etc. Animals including humans eat these plant parts.
Different parts of the plants used as food
|Part of plant||Examples|
To test the presence of starch in leaves:
Starch is colourless, but it turns blue-black in presence of iodine. To test for the presence of starch, a leaf is bleached by first boiling it in water and then in alcohol. The bleached leaf is washed in cold water and a few drops of iodine are added over it. If the leaf turns blue black, it confirms the presence of starch in the leaf.
To test the need of sunlight for photosynthesis:
To test the need of sunlight for photosynthesis, a plant is kept in a dark room for a day or two so that it does not make food for some time. Then, its leaf is covered partly with black paper and the plant is kept in sunlight for a few hours. Then the leaf which was partly covered is plucked, black paper is removed from the leaf and the leaf is bleached. The bleached leaf when tested with iodine solution will show blue black colour except for the covered part. This is because the part which was covered with black paper could not trap sunlight and could not produce starch.
To test the need of chlorophyll for photosynthesis:
To test the need of chlorophyll for photosynthesis, a coleus leaf is taken which is green and yellow in colour. It is bleached and washed in cold water. Then, a few drops of iodine are added to it. Only the green portion of the leaf turns blue-black.
3. INTERDEPENDENCE OF PLANTS AND ANIMALS
Energy is something which we need for doing any activity. This energy comes from food that is prepared by the green plants. Sunlight is the main source of energy on Earth. Green plants can trap this energy and convert it into food. Plants also give out oxygen during photosynthesis which is used by animals to breathe. Thus, animals depend on plants for food and oxygen. Animals breathe out carbon dioxide which is used by plants to make food. Thus, plants and animals are interdependent on each other.