Plants — Class 4 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 4 Science. How plants make their own food, the kinds of plants, and how they adapt to their surroundings.
1. Plants make their own food
Animals must find food. Plants make theirs, and this is the single most important fact about them.
The process is called photosynthesis, which means "putting together with light".
Carbon dioxide + Water + Sunlight energy gives Glucose + Oxygen
- Carbon dioxide comes from the air, entering through tiny pores in the leaves.
- Water comes from the soil, drawn up by the roots.
- Sunlight provides the energy, captured by chlorophyll, the green colouring in leaves.
- Glucose is the plant's food. It is used for energy and to build starch, cellulose and proteins.
- Oxygen is given off into the air — which is where the oxygen you are breathing right now came from.
Plants do not eat soil. This is worth being clear about. Roots take up water and minerals from the soil, but the plant's actual food is glucose, and the leaves make it. Soil is not swallowed.
Photosynthesis needs light, so it happens only during the day. But plants also respire — take in oxygen and release carbon dioxide — and that goes on day and night, just as it does in animals.
2. The five kinds of plants
| Kind | Description | Tamil Nadu examples |
|---|---|---|
| Herbs | Small, soft green stems | Tulsi, coriander, mint |
| Shrubs | Medium, bushy, hard stems branching near the ground | Hibiscus, jasmine, rose |
| Trees | Tall, one thick woody trunk | Neem, tamarind, coconut, banyan |
| Climbers | Weak stems that climb using support | Money plant, grape vine, betel |
| Creepers | Weak stems that spread along the ground | Pumpkin, watermelon, sweet potato |
The difference between a climber and a creeper is direction. Both have stems too weak to stand alone: a climber goes up something, a creeper spreads out along the ground.
3. Land plants and water plants
Terrestrial plants grow on land — neem, paddy, coconut.
Aquatic plants grow in water, and they come in three sorts:
- Floating on the surface, roots hanging free: duckweed, water hyacinth
- Fixed in the mud with leaves on the surface: lotus, water lily
- Underwater, wholly submerged: hydrilla, vallisneria
4. How plants adapt
An adaptation is a feature that suits a plant to where it lives.
Desert plants must save every drop of water. A cactus has leaves reduced to spines, so very little water escapes, and the spines also keep animals away. Its thick green stem does the photosynthesis instead of leaves, and stores water inside.
Aquatic plants have the opposite problem — too much water. A lotus has broad flat leaves that float, with a waxy waterproof upper surface so water rolls off, and its breathing pores on the upper side where the air is.
Mountain plants such as pine grow in a cone shape with sloping branches, so that snow slides off instead of breaking them.
5. Worked examples
Example 1. Write the word equation for photosynthesis.
Solution: Carbon dioxide + Water + Sunlight gives Glucose + Oxygen.
Example 2. What is the green pigment in leaves called, and what does it do?
Solution: Chlorophyll. It captures sunlight energy for photosynthesis.
Example 3. Do plants eat soil?
Solution: No. They absorb water and minerals from soil through their roots, but their food, glucose, is made in the leaves.
Example 4. Classify: tulsi, neem, pumpkin, hibiscus.
Solution: Tulsi is a herb, neem a tree, pumpkin a creeper, hibiscus a shrub.
Example 5. Why does a cactus have spines instead of leaves?
Solution: Spines lose very little water, which matters in a desert, and they also protect the plant from animals.
Example 6. Where are the breathing pores of a lotus leaf, and why?
Solution: On the upper surface, because the lower surface rests on water and only the top is in contact with air.
6. Practice
- What is photosynthesis?
- Name the four things a plant needs for photosynthesis.
- Which gas do plants release during photosynthesis?
- Name the five types of plants with one example each.
- What is the difference between a climber and a creeper?
- Give one example each of a floating, a fixed and an underwater plant.
- Name two adaptations of a cactus.
- Why do pine trees have sloping branches?
7. Answers
- The process by which plants make their own food using carbon dioxide, water and sunlight.
- Carbon dioxide, water, sunlight and chlorophyll.
- Oxygen.
- Herb (tulsi), shrub (hibiscus), tree (neem), climber (money plant), creeper (pumpkin).
- A climber grows upwards using support; a creeper spreads along the ground.
- Floating: duckweed. Fixed: lotus. Underwater: hydrilla.
- Leaves reduced to spines to cut water loss, and a thick green stem that stores water and does photosynthesis.
- So that snow slides off instead of collecting and breaking them.
8. Summary
- Plants make their own food by photosynthesis: carbon dioxide + water + sunlight gives glucose + oxygen.
- Chlorophyll, the green pigment, captures the sunlight.
- Plants do not eat soil; they take water and minerals from it and make food in their leaves.
- Photosynthesis happens only in light, but respiration continues day and night.
- The five kinds of plants are herbs, shrubs, trees, climbers and creepers.
- Climbers go up a support; creepers spread along the ground.
- Aquatic plants may float, be fixed in mud, or grow underwater.
- Cactus spines cut water loss; lotus leaves are waxy with pores on top; pines shed snow from sloping branches.
