Hands-On Science Textbook Primary 4 (Chapter 01)

Chapter

1

Life Cycles

All living things begin with birth and end with death.
Some animals have a short life cycle and some live
slightly longer. How are the life cycles of animals and
plants different?

What do I know about the life cycles of animals and plants?
1.
2.
3.

What do I want to know about the life cycles of animals and plants?
1. Recognize that all living things go through a life cycle and that life

cycles can be different for different living things.
2. Describe the life cycle of some animals.
3. Describe the life cycle of plants.

1.1 Life Cycles of Animals

All living things have life cycles. A life cycle shows the different stages through
which a living thing grows and changes. Different animals have different life
cycles. They undergo some changes in size and shape during different stages
in their life. Some young animals such as chickens and horses look like their
parents. However, there are some young animals that do not resemble their
parents.

Let’s Try! Do the baby animals look like their parents?

Things needed: • Sets of picture cards of baby animals
and their parents

1. Work in groups of five.
2. Give each group a set of picture cards of baby animals and their parents.
3. Mix up the picture cards.
4. Match the baby animals to their parents.
5. Does every baby animal look like its parents?

6. What are the differences between the baby animals and their parents?

7. What is your conclusion from this activity?

Let’s Find Out!

Look for pictures or photos of an example where:
• the baby animal looks like its parents
• the baby animal looks different from its parents
Show the photos and describe how the baby changes as it grows into an
adult. Share your findings with your friends in class.

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Some insects such as butterflies, beetles and mosquitoes undergo four different
stages in their life cycle. It is a complete metamorphosis. The stages are so
different that we might not recognize them as the same animal.

Life Cycle of a Butterfly

1 Egg

The eggs are laid on
a leaf by the adult
female butterfly.

4 Adult 2 Larva

The pupa emerges from the The larva of a butterfly, the
cocoon as an adult butterfly. caterpillar, eats a lot of leaves.
The adult butterfly is mature This is the feeding stage. As it
and can mate to produce eggs. grows, it molts a few times.
The adult female can fly from
place to place to look for the
right plant for its eggs.

3 Pupa

Later, it stops eating. It turns into a
pupa. This is the transition stage. The
pupa may hang under a branch or
hide in leaves. The pupa is protected
inside a cocoon.

Chapter 1 Life Cycles 3

Life Cycle of a Beetle

1 Egg

The eggs are laid on
a leaf by the adult

female beetle.

4 Adult 2 Larva

The pupa emerges The larva of the
from the cocoon as an beetle eats a lot of
adult ladybird beetle. It food and continues to
is mature and can mate grow. As it grows,
to produce eggs for the
beginning of another it molts a few
times.
generation.

3 Pupa

Later, it enters into
the ‘pupal stage’. It
attaches itself to the
stem of a plant. It

continues to
grow.

Molting is the shedding of the outer layer or covering to make
way for a new growth. Besides insects, mammals and birds
molt, too.

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Life Cycle of a Mosquito

1 Egg
The eggs are laid in
stagnant water.

4 Adult 2 Larva
The adult mosquito is The larva lives in the
mature and moves out water and comes to the
from the water surface. It surface to breathe. It
flies away and can mate eats a lot and molts a
to produce eggs. few times as it grows.

3 Pupa
The pupa does not eat
or move. It lives near
the water surface.

Mosquitoes breed in stagnant water. How do we reduce the
number of mosquitoes in our surroundings?
• Remove stagnant water in empty buckets or old tires to

prevent mosquitoes from laying eggs in them.
• Spray oil on the surface of water to choke the larvae and

pupae.
• Rear fish in stagnant water that will eat the larvae and pupae.

Chapter 1 Life Cycles 5

Life Cycle of a Grasshopper

The life cycle of a grasshopper is different from that of the mosquito. It has three
stages, namely, egg, nymph and adult. It is an incomplete metamorphosis.

1Egg

The eggs are laid in the soil.

Nymph 2

3Adult A nymph looks like an adult
grasshopper. It does not
An adult grasshopper has have wings. It molts a few
wings and it can fly. The times as it grows.
female grasshopper can lay
eggs when they are one or
two weeks old.

Let’s Think

What are the similarities and the differences in the life cycle of a mosquito
and a grasshopper?

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Life Cycle of a Cockroach

The life cycle of a cockroach is the same as that of a grasshopper. It has three
stages, namely, egg, nymph and adult.

1 Egg
The eggs are laid in
an egg case.

3 Adult 2 Nymph
An adult cockroach has A nymph looks like the
wings and it can fly. It is adult. It does not have
darker in color and larger wings and is smaller in
in size. It can lay eggs at size. It molts a few times
this stage. as it grows.

Cockroaches are one of Let’s Find Out!
the common pest problems.
They give off unpleasant Identify an insect that has the
odors and spread diseases. same three-stage life cycle as
Thus, we must get rid of a cockroach. Create a circular
them. Exposure to their diagram to represent the life cycle
feces over time can cause and share your findings with your
allergies. friends.

Chapter 1 Life Cycles 7

Life Cycle of a Chicken

Can you describe the life cycle of a chicken and a frog?

1 Egg

The eggs are laid in the nest. The eggs
have a hard shell to protect the young
inside. They use the egg yolk as a means
of nutrition as they grow.

3 Adult 2 Young

An adult chicken is A chick looks like
the adult. It will
able to reproduce by develop feathers.

laying eggs.

A hen lays a group of eggs
in a nest. The hen sits on
the eggs to incubate them.
The hen makes sure the
eggs get enough warmth
by incubating them for 21
days before they hatch.

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Life Cycle of a Frog

1 Egg

The eggs are laid in
water. The eggs have a

jelly-like covering.

3 Adult 2 Young

The adult frog does not The eggs will soon hatch
have a tail. It starts to eat into tadpoles. They look like
insects. It then lays eggs to fish and do not have legs.

begin the cycle again. They eat plants from the
water as they grow.

The life cycle of a frog is the same as that of a chicken. It has three stages in
its life cycle, namely, egg, young and adult.

Let’s Think

-Frogs lay eggs in water because their eggs do not have a hard shell

like birds. Their eggs are in the form of jelly like masses. Why are frog
eggs covered in jelly?

Chapter 1 Life Cycles 9

1.2 Life Cycles of Plants

The life cycle of most flowering plants consists of three main stages, namely,
seed, young plant and adult plant. The plant starts its life cycle as a seed. The
seed germinates and grows into a young plant. The young plant will increase
in size and height. The number of leaves and branches will also increase.

Life Cycle of a Pea Plant

1   Seed

With suitable conditions
such as air, water and warmth,
the seed will germinate into a
young plant. As a seed grows,
the roots grow first. Then, the shoot
appears. The leaves will grow later.

3   Adult plant 2   Young plant

When the plant has developed At first, the young
into an adult plant, it will plant gets its food
produce flowers. The flowers from the seed.
develop into fruits filled with When leaves are
seeds. The seeds will later grow formed, it starts
into new plants. making its own
food.
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Let’s Find Out!

Identify a flowering plant. Create
the life cycle of the plant with
pictures, and share it with your
friends.

Let’s Try! Which plant grows faster?

Things needed: • Tomato seeds • Green beans • Plastic cups

• Soil • Water • Ruler

1. Fill two plastic cups with soil. Spray some water onto the soil.

Tomato seed Plastic cups Green bean
Soil

AB

2. Place tomato seeds into cup A and green beans into cup B.
3. Spray water onto the soil in both cups every day.
4. Observe the growth of the seeds into seedlings.
5. Record your observations in the table below.

Seeds Date when seeds Date when seedlings The height of the
are planted start to appear seedlings on day

seven (cm)

Cup A

Cup B
6. Measure the height of the seedlings using a ruler on day seven.
7. Record your readings in the same table.
8. Which seeds grow first, the seeds in cup A or cup B?

9. Which plant grows taller and has more leaves?

10. What are the similarities or differences between the growth of both plants?

11. What is your conclusion from this activity?

Chapter 1 Life Cycles 11

Let’s Try! What do seeds need for germination?

Things needed: • Test tubes • Fresh mung beans
• Cotton • Oil
• Test tube rack • Water

1. Label four test tubes, A, B, C and D.
2. Put some moist cotton into test tubes A and B.

Beans Oil
Moist cotton
Cool boiled
water

Beans

ABCD

3. Put some mung beans into each test tube.
4. Pour some cool boiled water and some oil into test tube D.
5. Leave test tubes A, C and D near a window.
6. Put test tube B in a refrigerator.
7. Tick in the table below the availability of air, warmth and water to the mung

beans in the four test tubes.

Test tube Air Warmth Water Observation

A

B

C

D
8. Observe the beans after three days. Write your observations in the table

above.
9. What is your conclusion from this activity?

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Fill in the blanks. Some words can be used more than once.

pupa    adult    germinate    four    larva
    jelly-like    seed    nymph    three

1. There are stages in the life cycle of butterflies, beetles and
mosquitoes.

2. The stages in the life cycle of a beetle are egg, ,
and adult.

3. In the life cycle of a mosquito, the stage is where it molts a
few times.

4. The life cycle of grasshoppers and cockroaches has stages.

5. The stages in the life cycle of a grasshopper are egg, and
adult.

6. In the life cycle of a cockroach, the stage is where the
young looks like an adult.

7. The eggs of a chicken are different from the eggs of a frog which have a
covering.

8. In animal life cycles, the stage is where the animals are
ready to reproduce.

9. The basic stages of a plant’s life cycle are , young plant and
adult plant.

10. Seeds need water, air and warmth to .

Let’s Scan

Chapter 1 Life Cycles 13

Map It Out

Life cycles

Animals Plants

• Mosquito • Pea plant
Egg → larva → pupa →adult Seed → young plant
• Cockroach
Egg → nymph → adult → adult plant
• Frog
Egg →young →adult

Explain It Online

QuickQuiz

Cocoon

The soft covering that surrounds and protects particular insects
during the pupa stage as they develop into adult stage

Germinate

To start to grow and put out shoots

Incubate

When a hen incubates its eggs, it keeps them warm until the
young come out

Stagnant

Not moving or flowing

Transition

The process of changing from one state to another

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