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Natural Science & Technology: Grade 5
Life and Living: Life Cycles
LIFE CYCLES
A life cycle is the sequence of changes or development that an animal or plant goes through
in its life. A life cycle describes the stages and processes that take place as a plant or animal
grows and develops. The main stages of development are birth, growth, reproduction and
death.
Plants and animals must reproduce so that their species survive and do not become extinct.
The new offspring grows and develops and in time will also reproduce, and so the cycle of
life continues.
The Plant Life Cycle
Plants go through a number of stages in their life cycle, i.e. pollination, fertilisation, dispersal,
germination, growth and maturity, as shown in the diagram below.
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Life and Living: Life Cycles
1. Pollination
Pollination is the transfer of pollen from the stamens (male parts) of a flower to the stigma
(female parts) of the same flower, or to another flower. The pollen must reach the female
parts, before a seed can grow.
Flowers are mainly pollinated by pollen from other flowers of the same species. The
colourful petals attract insects such as bees, flies, moths and butterflies. The pollen clings to
the fine hairs on the insect’s body. Pollen is then transferred from one flower to another, as
the insect moves.
Bee Pollinating a Flower
The wind also causes pollination to take place in certain plants, such as conifers. Some
flowers have their pollen on the outside of their petals, so that the wind can blow it to other
plants easily.
Wind Pollination
Other plants are pollinated with the aid of water.
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Water Pollination
2. Fertilisation
Fertilisation is the fusion of the pollen with an ovule to make a seed.
The ovules are found in the ovary of a plant. A seed develops only after an ovule has been
fertilised. The pollen grains (male reproduction cells) move to the ovary of the flower and
fertilisation takes place. After the ovules fuse with the pollen, they become bigger and form
seeds.
Inside of Flower Showing Ovules
Wikimedia Creative Commons
Attribution Share-Alike: Tameeria
3. Dispersal (Scattering of Seeds)
Seeds must be carried away before they can grow into new plants. Plants scatter or disperse
their seeds in the following ways:
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Dispersal by Wind
When seeds land on the ground, they are blown away by the wind. Once they settle in a
suitable place and the conditions are right, they will germinate.
Dispersal by Animals
Acorns that are buried by squirrels, can grow into oak trees. The hooks of the seed of the
grapple plant can catch onto an animal’s fur and are dispersed in this way.
Fruits and berries are eaten by birds and are excreted in the birds' droppings. The seeds in the
droppings, if pollinated, can grow where they are dropped.
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Dispersal by Water
Seeds can fall into water such as rivers and streams and be dispersed as it flows downstream.
Dispersal with an Explosion
Some seed-pods, like the pea and the wisteria, explode to release their seeds.
Some seeds, like the squirting cucumber, can squirt out fluid containing seeds, when pressed.
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4. Germination
The process that a plant goes through when it starts to grow from a seed is called
germination. Germination is only possible if the plant has air, light, warmth, water and
nutrients.
The seed swells up with the water and then splits open. The primary root starts to grow. A
shoot then appears and reaches up towards the light. Germination has taken place when the
root and stem start to grow into a young plant.
Eventually the shoot will grow leaves and then the plant can make its own food, if it has
sunlight and water.
Another way to grow plants, is to use the cuttings of stems or leaves that come from existing
plants. This is known as vegetative reproduction.
Making a Cutting
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Cutting in Plant Pot
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Plant Growing in Pot
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5. Growth and Maturity
The plant grows into a seedling over a period of time and continues to grow until it reaches
maturity. A mature plant may produce flowers or bear fruits.
Mature Plant
The Animal Life Cycle
All animals reproduce. This means that they produce offspring. Reproduction ensures the
survival of the species.
Baby Birds Being Fed by Mother
Baby and Adult Turtle
Some animals, such as birds, lay eggs. Others, such as mammals give birth to live babies.
Most animals reproduce when the male sperm joins with the female egg.
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Reproduction - Male Sperm
Joining Female Egg
Some baby animals look just like the parent when they are born, while others first need to
undergo a metamorphosis (change) before they look like the adults.
Mother and Baby Rabbit
Mare and Foal
Some insects undergo an incomplete metamorphosis, for example, the locust, while others
undergo a complete metamorphosis, like flies, butterflies and moths.
Locust – Incomplete Metamorphosis
Butterfly – Complete Metamorphosis
A complete metamorphosis consists of the following stages: eggs are laid; larvae hatch; then
they develop into pupae from which the adults finally develop.
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Animals grow until they become mature adults and then they are able to reproduce so that the
cycle starts again. Death can occur at any stage in the life cycle.
Different types of animals have different life cycles as described below.
Go to the Grade 4 module on Features of Animals for more information on the different
groups of animals:http://www.mycyberwall.co.za/get-smart/science/grade-4/features-animals
Mammals
Mammals grow in a special way called gestation in the female's body. In humans, the
gestation period is 9 months. The gestation period varies from animal to animal.
Mammals do not hatch from eggs, the babies are born live and look like the parent.
Many mammals have more than one baby. The mother produces milk to feed the baby/babies
and cares for them until they become adults.
Dog Giving Birth
Newly Born Puppy
Puppy Growing
The mammal then mates and the cycle starts again.
Example – The Life Cycle of a Dolphin
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Gestation in a dolphin is between eleven and twelve months.
When the female dolphin gives birth, a pack of female dolphins surround the mother and
protect her from predators.
A baby dolphin can swim and breathe within a few minutes of being born. It will follow its
mother closely and feed from her milk for eighteen months to two years. The dolphin will
stay with its mother for three to eight years.
Mother and Baby Dolphin
Birds
Birds develop inside an egg. The egg is incubated by the adult bird. This means that the
parent/s keep the egg safe and warm. Once hatched, birds develop from the egg, to a chick, to
an adult.
Goose Incubating Eggs
Ostrich with Eggs
The baby bird (chick) hatches from the egg.
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Duckling Hatching
Chick
The chick is fed by its parent/s and once its feathers have developed, it will learn to fly. It
will leave the nest when it becomes an adult bird.
Young Bird Ready to Fly
After one year, the bird mates and has young of its own. The cycle begins again.
Example – The Life Cycle of a Penguin
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The mother penguin lays one or two eggs in a nest, which can be a circle of stones, grass or
an underground burrow.
Both penguin parents take turns to help the egg incubate. The male places the egg/s on his
feet to incubate it. Incubation takes around one to two months.
When the chick has hatched, both parents care for it. It has fur, not feathers when it is born.
When the penguin matures, it mates with one penguin for life.
Mother Penguin with Chicks
Fish
The life cycle of a fish varies, depending on the species, but generally progresses through the
following stages; egg, larval fish, fry, young fish to adult.
The female fish releases her eggs into the water and these are fertilised by male fish. This
process is called spawning. Usually thousands of eggs are released, so that some will survive,
as many are eaten by bigger fish.
Salmon Spawning
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Salmon Spawn
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When the eggs hatch, they are known as larval fish, as they have an egg sac attached to their
bodies, from which they feed. When this sac disappears, they are known as fry and they are
ready to start eating on their own.
The fry develop into young fish. Many fish do not survive long enough to become adults. The
fish is considered to be an adult when it is ready to reproduce. Fish with shorter life spans
reach maturity faster.
Some fish spawn every year after reaching maturity and others only spawn once and then die.
Example – Life Cycle of a Salmon
Salmon live in the sea but move to freshwater to reproduce.The female makes a nest and lays
the eggs in it. The male salmon then fertilises the eggs.
When the salmon hatch, they are known as alevins. They stay in the nest and have a food sac
attached to their bodies. Once the food sac is used up, the alevin becomes a fry and it leaves
the nest to search for insects to eat.
The fry matures and becomes camouflaged. It is then known as a parr. When its colour
changes to silver-grey, it is called a smolt. This usually takes six months to three years. Only
about 10% of salmon eggs survive to develop to this stage.
Once the salmon has grown, it swims back to saltwater. It returns to the place where it was
born in order to spawn. Most salmon die soon after spawning.
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Male and Female Salmon
Reptiles
The lizard, crocodile, tortoise and snake are examples of reptiles.
Lizard
Crocodile
Tortoise
Rattle Snake
Most, but not all reptiles, lay eggs. The incubation period varies between species. The eggs
have shells which are not hard, but feel more like leather. The shells are generally strong and
tough. The eggs are left in a warm, sunny place to hatch. Young reptiles look like their
parents when they are born.
Some snakes, like constrictors, give birth to live babies. They grow from eggs inside the
female’s body, then hatch inside her body and are born alive.
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Most baby reptiles are independent from the moment they hatch and can care for themselves.
Turtle Eggs
Baby Crocodiles Hatching
Example – The Life Cycle of a Python
The female python lays her eggs in shallow holes or under rocks. She will curl herself over
the eggs and protect them until they hatch, usually within two to three months. The young
snake leaves the nest soon after hatching.
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Baby Python
Young snakes reach maturity within two to four years. They shed their skin up to four times a
year, whilst mature snakes will only shed their skin once a year.
Adult Python
Amphibians
Amphibians, such as frogs, toads and newts have a more complicated life cycle than most
animals as they undergo a metamorphosis.
They are born live or from an egg, and spend their early days in the water, breathing through
their gills.
When they grow into an adult, they develop lungs and then live on land and water.
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Example - The Life Cycle of a Frog
The female frog lays thousands of eggs in the water.
Frog Spawn (Eggs)
After about ten days, the eggs hatch into tadpoles. The tadpole first breathes by means of gills
and lives only in the water. It uses its tail to swim.
Tadpoles
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The tadpole grows and becomes a froglet. Its back legs develop first. The froglet continues to
grow and its front legs develop. Then its lungs develop, its tail shrinks and its eyes and mouth
get bigger.
Froglet
The tail then disappears and the froglet becomes a frog. The adult frog breathes by means of
lungs and can live on land or in the water.
Adult Frog
Insects
Insects develop from an egg to a larva, to a pupa, then to the adult insect. We say that
metamorphosis is complete because there are four stages of development.
Beetle Laying Eggs
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Butterfly Laying Eggs
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Butterfly Eggs
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The larva looks a bit like a worm and this is when most of the feeding is done.
Larva
Pupa
The pupa stage is between larva and an adult. At this stage, the pupa is inactive and does not
feed.
Caterpillar Emerging from Larva
Once the insect becomes an adult, it often has wings.
Adult Butterfly
Some insects go through an incomplete metamorphosis. This is when they do not have a
pupa form. They change overnight from a larva to an adult.
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Insects such as grasshoppers, cockroaches and dragonflies only have the three stages and go
through incomplete metamorphosis.
Incomplete Metamorphosis – Cockroach
Incomplete Metamorphosis – Dragonfly
Example – The Life Cycle of a Fruit Fly
Each female fruit fly can lay fifteen to fifty eggs per day and up to nine hundred eggs in a
lifetime. She lays her eggs in the skin of fruit, which then quickly rots and falls from the
trees. The rotting fruit pulp is the source of food for the larvae that hatch.
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After a few days, the larvae will crawl into the ground and change into pupae. The mature fly
appears from the pupa after about two to three weeks.The entire life cycle of the fruit fly lasts
about two weeks.
Adult Fruit Fly
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