Life of Animals — Class 4 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 4 Science. Life cycles, how animals are born, what they eat, and which of them are in danger.
1. Life cycle of a butterfly
Some animals change shape completely as they grow. This is called metamorphosis, and the butterfly is the classic example.
| Stage | What happens |
|---|---|
| Egg | Tiny, laid on a leaf |
| Caterpillar (larva) | Eats leaves constantly, grows fast, sheds its skin four or five times |
| Pupa (chrysalis) | Forms a hard case; inside, the body is completely rebuilt |
| Adult butterfly | Emerges with wings, flies, and drinks nectar |
The caterpillar and the butterfly look nothing alike, yet they are the same animal at two stages of one life.
2. Life cycle of a frog
| Stage | What happens |
|---|---|
| Egg | Laid in water in a jelly-like mass |
| Tadpole | Has gills and a tail, swims, lives entirely in water |
| Froglet | Grows legs, the tail shrinks, lungs develop |
| Adult frog | Breathes with lungs, lives on land and in water |
A tadpole is not a fish. It looks like one at first, with gills and a tail, but it gradually grows legs, loses its tail and develops lungs. A fish never does.
3. How animals are born
| Type | Meaning | Examples |
|---|---|---|
| Oviparous | Lay eggs; the young develop outside the mother's body | Hen, crow, sparrow, most fish, frog, turtle, crocodile, insects |
| Viviparous | Give birth to live young that develop inside the mother | Dog, cat, cow, human, whale |
A useful check: a whale lives in water and looks like a fish, but it gives birth to live young and feeds them milk, so it is viviparous — a mammal. And a few fish, such as guppies, give birth to live young too, so "lays eggs" is about the animal, not about where it lives.
4. What animals eat
| Group | Diet | Examples |
|---|---|---|
| Herbivores | Plants only | Cow, goat, deer, elephant, rabbit |
| Carnivores | Other animals | Tiger, lion, eagle, snake |
| Omnivores | Both plants and animals | Crow, bear, human |
5. Food chains
A food chain shows who eats whom, and so how energy passes along.
Grass gives energy to the deer, and the deer gives energy to the tiger.
Every food chain begins with a plant, because only plants make their own food. Remove the grass and the deer starves; remove the deer and the tiger has nothing to hunt. Each link depends on the one before it.
6. Endangered animals
An endangered species is one whose numbers have fallen so low that it is at risk of dying out completely.
The causes are almost always human: loss of habitat through deforestation, hunting and poaching, pollution, and climate change.
Endangered animals with a Tamil Nadu connection:
- Bengal tiger — protected in the Mudumalai and Anamalai reserves
- Asian elephant — found in the Nilgiris and the Western Ghats
- Asiatic lion — now only in Gir, Gujarat
- Nilgiri tahr — the state animal of Tamil Nadu, a wild goat of the high hills
- Great Indian bustard and the olive ridley turtle, which nests on the Tamil Nadu coast
Protecting them means protecting where they live. National parks, wildlife sanctuaries and tiger reserves exist for exactly that.
7. Worked examples
Example 1. Name the four stages of a butterfly's life cycle in order.
Solution: Egg, caterpillar (larva), pupa (chrysalis), adult butterfly.
Example 2. What is a tadpole?
Solution: The young stage of a frog. It lives in water and breathes with gills.
Example 3. Classify as oviparous or viviparous: hen, cow, frog, whale.
Solution: Oviparous — hen, frog. Viviparous — cow, whale.
Example 4. Why is a whale not a fish?
Solution: It gives birth to live young and feeds them milk, so it is a mammal, even though it lives in water.
Example 5. Complete the food chain: grass, ___, tiger.
Solution: Deer.
Example 6. Why must every food chain begin with a plant?
Solution: Because only plants make their own food. Every animal depends, directly or indirectly, on that food.
Example 7. Name the state animal of Tamil Nadu.
Solution: The Nilgiri tahr.
8. Practice
- What is metamorphosis?
- Name the stage between caterpillar and adult butterfly.
- Give two differences between a tadpole and an adult frog.
- What does oviparous mean? Give two examples.
- Give two examples of viviparous animals.
- Classify a crow by its food habit.
- Write a food chain of three living things.
- Name three endangered animals found in India.
- Give two causes of animals becoming endangered.
9. Answers
- A complete change of body form as an animal grows, as in a butterfly or frog.
- The pupa or chrysalis.
- A tadpole has gills and a tail and lives in water; an adult frog has lungs and legs and lives on land and in water.
- Laying eggs, so the young develop outside the mother's body. Hen and frog.
- Cow and dog (also cat, human, whale).
- Omnivore — it eats both plants and animals.
- Grass gives energy to deer, and deer to tiger.
- Bengal tiger, Asian elephant and Nilgiri tahr (also Asiatic lion, great Indian bustard).
- Loss of habitat through deforestation, and hunting or poaching.
10. Summary
- Metamorphosis is a complete change of body form during growth.
- Butterfly: egg, caterpillar, pupa, adult. Frog: egg, tadpole, froglet, adult.
- A tadpole is a young frog, not a fish; it swaps gills and tail for lungs and legs.
- Oviparous animals lay eggs; viviparous animals give birth to live young.
- Herbivores eat plants, carnivores eat animals, omnivores eat both.
- Every food chain starts with a plant, because only plants make their own food.
- Endangered species are at risk of dying out, mainly from habitat loss, poaching, pollution and climate change.
- The Nilgiri tahr is the state animal of Tamil Nadu.
