The basic parts of almost all plants are roots, stems, leaves, flowers, fruits, and seeds. We'll look at the root, stem, leaves, fruits and seeds in this module.
Stems carry water and nutrients taken up by the roots to the leaves. Then the food produced by the leaves moves to other parts of the plant. Stems also provide support for the plant allowing the leaves to reach the sunlight that they need to produce food.
To understand the movement of water up the stem we can place a cut stem and place it in a glass of water that has red ink mixed with it. On observing the stem the next day we will notice that parts of the stem appears to have red colour. On cutting across the stem we can see a number of spots of red colour arranged in a ring inside the stem.
This indicates that water moves up the stem. In other words, stem conducts water. Just like the red ink, minerals dissolved in water also move up in the stem, along with the water.
Leaves are the food making factories of green plants. Leaves come in many different shapes and sizes. The part of a leaf by which it is attached to the stem is called petiole. The broad, green part of the leaf is called lamina.
If you put a leaf under a white sheet of paper and hold your pencil tip sideways and rub it on the portion of the paper having the leaf below it, you will get an impression with some lines in it. These lines on the leaf are called veins. A thick vein seen in the middle of the leaf is called the midrib. The design made by veins in a leaf is called the leaf venation. If this design is net-like on both sides of midrib, the venation is reticulate. In the leaves of grass you might have seen that the veins are parallel to one another. This is parallel venation.
Leaves perform various functions. Water comes out of leaves in the form of vapour by a process called transpiration. Plants release a lot of water into the air through this process.
We can study this using a healthy, well watered plant that has been growing in the sun. A leafy branch of the plant is enclosed in a polythene bag and the mouth of the bag is tied up. Then an empty polythene bag is also tied up and both these are kept in the sun. After a few hours, when we observe the inner surface of the bags we will notice droplets of water in the bag enclosing the leafy branch of the plant. This small experiment helps us see the process of transpiration of plants.
Leaves also prepare their food in the presence of sunlight using a green coloured substance present in them. For this, they use water and carbon dioxide from air. This process is called photosynthesis. Oxygen is given out in this process. The food prepared by leaves ultimately gets stored in different parts of plant as starch.
The roots help provide support by anchoring the plant and absorbing water and nutrients needed for growth. They can also store sugars and carbohydrates that the plant uses to carry out other functions.
Plants can have either a taproot system (such as carrots) or a fibrous root system (such as turf grass).
A taproot has a main root and the smaller roots are called lateral roots. Fibrous roots do not have any main root and all the roots seem similar. In both cases, the roots are what carry the water and nutrients needed for plants to grow.
We have learnt that roots absorb water and minerals from the soil and the stem conducts these to leaves and other parts of the plant. The leaves prepare food. This food travels through the stem and is stored in different parts of a plant. We eat some of these as roots— like carrot, radish, sweet potato, turnip and tapioca. We also eat many other parts of a plant where the food is stored.
If you look at plants, you will see that those with parallel leaf venation have fibrous roots and those with reticulate leaf ventilation have taproot, which is a very interesting observation.
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