4th Standard Science Term-II
Plants
Introduction
All living things need food. Food helps them grow and perform daily activities. We have seen animals eating their food. But, have you ever wondered how plants get their food? Plants produce their own food with the help of chlorophyll, a pigment present in leaves. Humans and animals depend on plants for their food either directly or indirectly. Let us learn more about plants in this lesson.
I. Parts of Leaf
Leaves are of different shapes and sizes and have different parts. However, there are some basic parts that are common in most of the leaves.
Blade : The broad flat part of the leaf(Lamina).
Apex : The tip of the leaf.
Midrib : The midrib runs along the centre of the leaf.
Veins : Veins branch out form the midrib. They are the framework of hollow tubes that carry water and minerals.
Petiole : This part joins the leaf to the main stem.
Stomata : Stomata are tiny openings or pores mostly found at the base of the leaves. Air enters and leaves the plant through these openings. Stomata helps the plants to breathe. Stomata are used to exchange gases.
1. Leaf as food factory
Plants need food but they never depend on people or animals to get their food. Most of the plants are able to make their own food through a process called photosynthesis.
Photosynthesis = Photo (light) + synthesis (make)
Photosynthesis is a process by which plants make their food using chlorophyll water and carbon dioxide in the presence of sunlight. Let us see how this process is organized within the plants.
Water : Water is absorbed by the roots and is transported to the leaves through the tubes.
Carbon dioxide : Carbon dioxide in the air passes through stomata in the leaves.
Sunlight : A green pigment in the leaves help them to trap sunlight. This pigment is called chlorophyll. Most leaves are green in colour because of this green pigment
Through photosynthesis plants produce the food and release oxygen into the air.
Sun light
Water + Carbon dioxide ➜ Food + Oxygen
Chlorophyll
As plants prepare food for themselves and also for other living things, they are called primary producers.
Without primary producers, living things are not capable of producing their own food and will not be able to live.
More to Know
In plants like cactus, leaves are modified into thorns. Their food is produced in the green stems.
II. Classification of Plants
Plants are classified in many ways based on stems, life span, seeds, flower and colour. In this section we will study about the classification of plants based on flower and colour (pigment).
1. Flowering and Non-flowering plants
Flower is the most important part of many plants, because it is involved in reproduction. But some of the plants are not having flower. These plants reproduce in different modes. Based on this, plants can be classified into two types.
❖ Flowering plants
❖ Non-flowering pants.
Flowering plants
Plants bearing flowers are called flowering plants. Some of them reproduce by sex cells or gametes and produce seeds. Seeds produce new plants. Eg - Mango, Neem, Groundnut, Paddy etc.
Non-flowering plants
Plants that can reproduce without flower are called non-flowering plants. These plants to not produce seeds. They reproduce by a special structure called spores. E.g. Algae, Fungi, Fern.
2. Green and Non-green plants
The most important pigment present in plants are called chlorophyll. Based on the colour present in the plant, they are divided into two groups. They are green and non-green plants.
Green Plants
Plants containing green pigments are called green plants. It looks green in colour. They prepare their own food with the help of them. It depends on atmosphere, light and pigment for food preparation. Green plants are commonly called autotrophs.
E.g. Grass, Paddy, Algae etc.
Non-green plants
Plants that do not contain chlorophyll pigment and do not look green and called non-green plants. They cannot prepare their food. These plants depend on other organism for their food and living place. These are commonly called heterotrophs.
Sepal : Sepals are leaves that protect the flower while it is still a bud. Sepals are usually green or brown.
Petal : Petals are often bright coloured. Their main job is to attract insects such as bees or butterflies, to the flower. The insects help the flowers in the transfer of pollen grains.
Stamen : Stamen can be seen at the centre of a flower. They contain pollen grains that help the plants to multiply. It is the male part of a flower.
Pistil : Pistil is also seen at the centre of the flower. The pistil uses the pollen to help the flower to become fruit. It is the female part of a flower.
More to Know
The largest flower in the world is Rafflesia. This rare flower is found in the rainforests of Indonesia.
Seasonal Flowers
The change in climate that occurs periodically is called seasons.
There are four general seasons - Spring, Summer, Autumn and Winter.
Most flowers bloom in a specific season. Hence, they are called seasonal flowers.
More to Know
Firecracker flowers bloom in all seasons
Kurinji flower blooms once in 12 years
IV. Exotic Plants
The plants that grow outside their native area either purposefully or accidentally are called exotic plants.
Most of these plants are brought to new areas for decoration purposes. Some of them are given below.
More to Know
Parthenium plant accidentally grow in a new native. This plant expands its range and disturbs the cultivation areas. The pollen of this plant is allergic in nature. So, do not touch this plant wherever you see.
V. Plants as Food
Humans and other animals often use plants as food. Plants which we eat are edible. Edible parts of some plants include leaves, stems and roots. We also eat fruits produced by plants.
Edible parts of plants
All the parts of different plants are edible, that is, we can eat them as food.
Roots as food
Many plants store excess food in their roots. They have thick and swollen roots. These roots are used as food. Some of them are given below.
Stems as food
In some plants the stem stores the excess food in it. Potato, onion and ginger are the underground stems that we eat. Some of them are given below.
Leaves as food
Leaves of some plants are used as food. In some plants extra food is stored in leaves. We eat the leaves of some plants like cabbage. Some of the leaves used as food are given below.
Flowers as food
Flowers are the part of a plant. Many flowers are used as food. Some of them are given below.
Fruits as food
Many fruits are used as food. Fruits are rich in vitamins and minerals. They keep us healthy. All fruits can be eaten raw.
Grains as food
Grains of pulses, cereals and pods are the commonly eaten seeds. They are the rich sources of carbohydrates and proteins.
More to Know
Trees are the longest living organism on earth. Bamboo plants can grow upto 90 cm in a day.
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