Category : 4th Class
We often see beautiful trees, plants full of green leaves, around us. But do we ever think why the leaves of trees are green? Have you ever seen plants having coloured leaves? The leaves of most of the plants are green because their leaves contain a green coloured pigment called chlorophyll. Green leaves are responsible for making food. Thus, they are also known as food factories of the plants. Plants uses carbon dioxide, sunlight and water for making food. Upper surface of a leaf has more chlorophyll for trapping the sunlight. On the undersurface of the leaf, there are tiny pores known as stomata which can only be seen through microscope. The stomata are responsible for exchange of gases in plants. Water and essential minerals are absorbed by the roots of the plant from soil and then It is transported to leaves through Stem. On the undersurface of leaves, there are fine network of lines called veins. Main vein is located at the centre of the leaf called midrib. Main vein has two tubes. One tube carries water and minerals from the stem to the leaf. The other one takes food from the leaf to other parts of the plant. A leaf is attached to the stem by a stalk.
The process of making food by plants in the presence of sunlight, water, carbon dioxide and chlorophyll is called photosynthesis. During photosynthesis, plants take carbon dioxide and release oxygen. Food is prepared by plants in the form of glucose. Plants store extra food in fruits and seeds as starch. Trees store food in their trunks in the form of cellulose. Cactus do not have leaves. Photosynthesis occurs in their stems.
Some plants are not green. For example, mushroom. Another plant like croton plant has red coloured leaves. The red colour of the leaves is due to the presence of anthocyanin. But they have chlorophyll also. Photosynthesis takes place in these plants also.
Mushrooms do not have chlorophyll. They cannot make their food from photosynthesis. They get food from dead plants and animals.
Classification of Plants
Plants are of various types classified on the basis of where they grow.
Plant that grows on land are called terrestrial plants. They are further divided into various types such as:
Plants in hilly areas
In hilly areas, plants can make food easily as there is sufficient sunlight and rainfall in these places. Coniferous tree grows on hills and mountains.
They have standing branches so that snow which falls on them gets down. Conifers are generally evergreen as they do not shed their leaves. They do not produce flowers. Their leaves have few stomata only.
Plants that grow in hot places like deserts are called desert plants. Their leaves are modified into spines. Instead of leaves, food is prepared in stems.
Plants in plain areas
Plants or trees in plain areas have flat leaves that are useful for keeping them cool in hot conditions by evaporating water. Trees like gulmohar, peepal lose their leaves in winters and grow new ones in warm times.
Plants in marshy land
Marshy land has sticky soil with lots of water. We call them mangroves. Examples are ceriops and cattails. Roots of mangrove tree do not get air from soil. Thus, they have breathing roots out of the soil.
Plants which grow in water are called aquatic plants. They are of three types which are as follows:
Plants which float freely in water are floating plants. They have spongy, air filled parts to help them float. Their roots are not well developed. Their leaves have waxy coating to prevent blockage of stomata. Duckweed, water lettuce are some floating plants.
Duckweed Water lettuce
Plants which have their roots fixed in mud at the bottom are called fixed plants. They have light and hollow stems which helps the leaves and flowers to float. They have flat and big leaves to have enough stomata on the upper side. Lotus and water lily are the examples of fixed plants.
Lotus Water lily
The plants which grow under the water are called underwater plants. Hydrilla and tape grass are some underwater plants.
Hydrilla Tape grass
Their narrow leaves do not have stomata. These plants use carbon dioxide dissolved in water to prepare their food.
The plants which trap insects to get essential minerals required for making food are called insectivorous plants. Venus flytrap, pitcher plant are some insectivorous plants.
These have long hairs along the edges of the leaves so that when an insect touches the hair, the leaf shuts and insect got trapped inside it.
Venus flytrap Pitcher plant
Grasses are very small plants which grow in mil conditions that is neither too dry nor too wet. Grasses need a little amount of water only. Rice, wheat, maize and bamboo belong to this family.
Use of grasses
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