P3 Life Cycle of Animals 🐣
Created by Miss Clarissa Ng | www.clartutors.com
1 What is a Life Cycle?
- For most animals, the females reproduce by laying eggs. The different stages, from egg to adult, make up the life cycle of an animal.
- Animals have life cycles as it ensures the continuity of their own kind.
- A life cycle has no starting or ending point.
🔄 Fun Fact: A life cycle has no starting or ending point — it's like a circle that goes on forever! That's why we call it a "cycle".
🕑 Development Time
- The time it takes for the young of an animal to develop into an adult can vary for different animals.
🥚 Eggs
- Different animals lay different numbers of eggs.
- Animals that do not care for their young, like most fish, insects and amphibians, may lay large numbers of eggs at one time.
- This increases the chances of the eggs hatching and the young surviving to adulthood to reproduce and continue the life cycle.
🐟 Fun Fact: A single codfish can lay up to 9 million eggs! Since they don't take care of their babies, they need lots of eggs so some survive.
🏠 Habitat
- Some animals spend their life cycle entirely on land while others spend it partly in water.
🐸 Fun Fact: Frogs are amphibians — they start life in water as tadpoles, then grow legs and move to land as adults. They literally live two lives!
👁 Appearance
- The young of some animals look like or resemble the adult.
- Other animals have young that do not look like or do not resemble the adult.
🐣 Fun Fact: Baby chicks look just like tiny versions of their parents — they hatch with feathers and can walk right away! That's called resembling the adult.
🎯 Number of Stages
- Animals can have a different number of stages in their life cycles.
- Most animals have three stages in their life cycles, while others have four stages in their life cycles.
📌 Exam Tip! Use HAS when comparing life cycles of animals — Habitat, Appearance, Stages!
2 Three-Staged Life Cycles
🥚
Egg
→
Egg
🐣
Young
(Nymph)
→
Young
(Nymph)
🐥
Adult
Adult
| 🐤 Chicken | 🐸 Frog | 🐜 Cockroach | 🦗 Grasshopper |
|---|---|---|---|
| Life cycle takes place entirely on land | Life cycle takes place partly in water | Life cycle takes place entirely on land | Life cycle takes place entirely on land |
| Young resembles the adult | Young does not resemble the adult | Young resembles the adult | Young resembles the adult |
🦋 Fun Fact: A butterfly's life cycle takes place entirely on land — from egg to adult, it never enters water!
🦗 Insects with Three Stages
- The young of an insect with a three-staged life cycle is known as a nymph.
- To develop from a nymph to an adult, an insect undergoes moulting.
- An insect moults to shed its hard outer covering in order to grow bigger.
🦗 Fun Fact: Grasshoppers moult about 5 times before becoming adults — each time they shed their old skin and grow a new, bigger one!
| Nymph | Adult |
|---|---|
| Does not have wings | Has wings |
| Cannot fly | Can fly |
| Undergoes moulting | Does not moult |
| Cannot reproduce | Can reproduce |
3 Four-Staged Life Cycles
🥚
Egg
→
Egg
🐛
Larva
→
Larva
Pupa
→
🦋
Adult
Adult
- Animals such as the mosquito, mealworm beetle and the butterfly have life cycles that consist of four basic stages — egg, larva, pupa and adult.
- Insects with four-staged life cycles undergo moulting in the larval stage.
🦋 Fun Fact: A butterfly caterpillar can eat up to 2,000 times its body weight before turning into a pupa -- that is like a human eating an elephant!
- In the larval stage, the animal feeds the most as it grows in size.
- Once the larva has grown fully, it enters the pupal stage, in which the animal does not feed.
🐛 Fun Fact: Mealworms are actually beetle larvae! They transform from wriggly worms into tough, armored beetles -- a complete makeover!
- During the pupal stage, the insect undergoes a drastic change in its appearance to become an adult.
- All animals with four-staged life cycles have young that do not resemble the adult.
🦋 Butterfly vs. Mosquito
| 🦋 Butterfly | 🦟 Mosquito |
|---|---|
| Life cycle takes place entirely on land | Life cycle takes place partly in water |
| Young does not resemble the adult | Young does not resemble the adult |
| Considered a pest in larval stage as it feeds on large amounts of leaves, causing damage to plants. | Considered a pest in adult stage as female mosquitoes feed on human blood and can spread diseases such as dengue. |
🦟 Fun Fact: Only female mosquitoes bite -- they need blood from humans and animals to develop their eggs. Males just drink nectar!
🛠 Mosquito Control
- The female mosquitoes lay their eggs in stagnant water.
- Mosquitoes are the easiest to eliminate in the egg, larval and pupal stages as they cannot fly.
🏠 Fun Fact: The WSG (Weekly Source Inspection) campaign in Singapore gets everyone to check for stagnant water every week -- because even a bottle cap full of water can breed mosquitoes!
- Spraying oil on the surface of the water blocks the breathing tubes of the larva and pupa of the mosquito and prevents them from taking in oxygen.
- It is most difficult to kill mosquitoes in the adult stage as they can fly and escape easily.
4 Comparing Life Cycles
🦋 Butterfly vs. Grasshopper Comparison
| 🦋 Butterfly (4 stages) | 🦗 Grasshopper (3 stages) |
|---|---|
| Egg → Larva → Pupa → Adult | Egg → Nymph → Adult |
| Life cycle takes place entirely on land | Life cycle takes place entirely on land |
| Young does not resemble the adult | Young resembles the adult |
📊 Fun Fact: The main difference between a 3-stage and 4-stage life cycle is the pupa stage -- in 3 stages, the young (nymph) looks like the adult; in 4 stages, it goes through a total transformation!
📊 Reading Life Cycle Graphs
When you see a bar graph showing days at each stage, remember these key calculations:
Egg
Larva
Pupa
Adult
Insect X (Total: 31 days)
Insect Y (Total: 31 days)
- If an insect has egg, larva, pupa and adult stages — it has a four-staged life cycle.
- Time from egg to adult: Add days spent as egg + larva + pupa. (e.g., Insect X: 5 + 12 + 8 = 25 days)
- Time after hatching to adult: Add days spent as larva + pupa (exclude egg). (e.g., Insect Y: 14 + 6 = 20 days)
- Total life cycle duration: Add all four stages together. (e.g., Insect X: 5 + 12 + 8 + 6 = 31 days)
📈 Fun Fact: When comparing life cycle graphs, always check which stage takes the longest -- it is usually the larval or nymph stage because that is when the animal grows the most!