Objective of the chapter: How Plants Make Food - Class 4
You will learn:
- why plants are important for us
- about photosynthesis and the role of chlorophyll in it
- why plants and animals are dependent on each other
All green plants make their own food and the process by which plants make food is called photosynthesis.
We will learn more about photosynthesis later in this chapter.
Let's first learn why leaves of most the plants are green in colour.
Why Are Leaves Green In Colour?
Almost every plants look green because of their green leaves. Do you know what makes the leaves green?
Leaves have a green substance that gives them the green colour. This green substance is called Chlorophyll.
Chlorophyll is necessary for plants to make food for themselves.
Did you know that non-green living things cannot make their own food? Due to the absence of chlorophyll they are not able to make food. For example, mushrooms do not contain chlorophyll and that is why they cannot make food for themselves.
How Do Plants Make Their Own Food?
The process by which plants make their own food is called photosynthesis. 'Photo' means light and 'synthesis' means putting together.
Do you know what are required by plants to make food?
Leaves use water from the soil, carbon dioxide from the air and sunlight to make food.
The water needed to make food is taken up from the soil by the roots. It goes up the stem to the leaves.
If you observe a leaf carefully, you can see that it contains lines all over it. These lines are tubes that take water to all parts of the leaf. They are called veins.
Leaves contain very small openings called stomata. These openings are so small that it cannot be seen through your eyes.
Air enters the leaves through stomata. Leaves take in carbon dioxide from the air to make food.
Sunlight provides the energy needed to make food. Some part of the sunlight falling on a leaf is trapped by chlorophyll.
Using the energy of trapped sunlight, leaves change water and carbon dioxide into a kind of sugar which is the food of the plant. This food is taken through the veins and the stem to all parts of the plant.
A part of the food is changed into other substances and used up by the plant for:
- making flowers, fruits and seeds
- repairing damage
The rest is changed to a substance called starch and stored in fruits, seeds, leaves, roots or the stem.
When we eat food from plants, we actually eat the sugar, starch and other substances that the plants make for themselves.
How Plants And Animals Are Dependent On Each Other?
Living things cannot survive without oxygen. They use oxygen in the air to breathe.
When living things breathe, they take in oxygen and gives out carbon dioxide.
During photosynthesis, leaves take in carbon dioxide from the air and give out oxygen.
This shows that animals and human being are depend on plants for oxygen, and plants depend on animals for carbon dioxide.
Do you know why we should maintain the balance between the number of plants and animals in nature?
We know that:
- herbivores eat plants,
- carnivores eat herbivores and
- omnivores eat both plants and animals
This shows that all animals are dependent on plants for food.
In nature, we should maintain balance between the plants and animals. Because if there is no balance, plants will not get enough carbon dioxide to make food. And animals will not get food and oxygen from plants.
That is why we should protect nature to maintain the balance of plants and animals.