Science: Grade 5
Life and Living: The Life Cycle of Plants
THE LIFE CYCLE OF PLANTS
Plants depend on food, water, nutrients and oxygen in order to survive. They get these from
the Sun, the soil and the air.
Plants Make Food from Sunshine
Plants need Water
Sunlight
We saw in Grade 4 that plants can manufacture their own food. This process takes place in
the leaves and is known as photosynthesis.
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Life and Living: The Life Cycle of Plants
Plants take up the gas, carbon dioxide, from the air. They also absorb water from the soil,
capture the light energy from the Sun in their leaves (chlorophyll) and change the water and
carbon dioxide into energy-rich food.
Plants need Sunshine
In this way, the plant is able to grow and also serves as food for animals. This process takes
place only during the day.
Water and Nutrients
Apart from sunlight, plants need good soil in which to grow. No plant could grow without
soil. People and animals would have no food to eat if there was no soil.
The soil provides the plant with nutrients and water. It also anchors the plant into the ground
by its roots, so that it does not get blown or washed away.
Soil
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Soil Anchors Plants by their Roots
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The topsoil contains the nutrients that the plant needs. The plant takes the nutrients, along
with water, from the soil, through its roots. The nutrients dissolve in the water.
Fertilisers and Nutrients
Added to the Soil
Plants Absorb Nutrients and Water
from the Soil
The soil needs to be rich in nutrients for the plant to grow. This is why farmers sometimes
need to add fertiliser to the soil, which contains nutrients that the plants need.
Different parts of the plant are involved in transporting the water and nutrients throughout the
plant. These are the roots, the stem and the leaves. The nutrients are needed for the plant to
grow and the water is needed to transport the nutrients to the leaves. The water is also needed
to help with photosynthesis. It is difficult for plants to grow without water.
Nutrients and Water are Transported
through the Plant
Soil is made of organic (living) and inorganic (non living) matter.
Soil is formed very slowly over thousands of years through a process known as weathering.
Go to the module on Surface of The Earth for more information:
http://www.mycyberwall.co.za/get-smart/science/grade-5/surface-earth
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Life and Living: The Life Cycle of Plants
Soil erosion is when the top soil is blown or washed away. Small particles of sediment are
taken away as the Earth’s surface becomes worn down.
Plants cannot grow in areas where there is no topsoil and animals cannot live there. In areas
where the soil has become eroded, the soil is less fertile.
Soil Erosion
Infertile Soil
Water is lost from the plant in a process called transpiration, which is similar to evaporation.
Transpiration or water loss allows carbon dioxide to get into the leaves from the air and to be
used in the photosynthesis process.
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Life and Living: The Life Cycle of Plants
Carbon Dioxide
Carbon dioxide from the air is needed by plants for the process of photosynthesis.
Plants take the carbon dioxide from the air. Carbon dioxide and water combine with light
from the Sun to create oxygen and glucose. The glucose is used by the plant as energy.
Carbon dioxide is a greenhouse gas that causes global warming, so plants play an essential
role in removing carbon dioxide from the atmosphere and adding oxygen back into the air we
breathe.
Plants take Carbon Dioxide
out of the Air
Plants are Important to Humans and Animals
Most living things breathe in oxygen and breathe out carbon dioxide, however plants do the
opposite. When photosynthesis occurs, the process releases oxygen into the atmosphere. So
plants breathe in carbon dioxide and breathe out oxygen.
Therefore plants are extremely important to humans and animals as they provide oxygen
as well as get rid of the carbon dioxide in the air.
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Life and Living: The Life Cycle of Plants
The Plant Life Cycle
Plants go through a number of stages in their life cycle, i.e. pollination, fertilisation,
germination and growth, as shown in the diagram below.
Pollination
Flowers have both male and female parts on the same flower. The female parts are the
stigma, style and ovary. These parts are known as the pistil.
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Life and Living: The Life Cycle of Plants
The male parts are the anther and the filament. These parts are known as the stamen.
Pollination is the transfer of pollen from the stamens of a flower to the stigma of the same
flower or to another flower. The pollen needs to reach the ovules, before a seed can grow.
Flowers are mainly pollinated by pollen from other flowers of the same kind. 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 along.
Bee Pollinating a Flower
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Life and Living: The Life Cycle of Plants
The wind also causes pollination to take place in certain plants, such as conifers. Some
flowers have their stamens on the outside of their petals, so that the wind can blow their
pollen to other plants move easily.
Wind Pollination
Other plants are pollinated with the aid of water.
Water Pollination
Fertilisation
Fertilisation is the fusion of the pollen with the ovule to make a seed.
The ovules are in the ovary before they are reached by the pollen. After the ovules fuse with
the pollen, they becomes bigger and form seeds.
Inside of Flower Showing Ovules
Wikimedia Creative Commons
Attribution Share-Alike: Tameeria
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Life and Living: The Life Cycle of Plants
A seed develops only after an ovule has been fertilised. The pollen grains (male reproduction
cells) move from the stamens and fall onto the stigma (pollination), from where they move
down the style to the ovary of the flower. The pollen tube grows into the ovule and
fertilisation takes place. Now it is possible for the ovules to develop into seeds.
Dispersal (scattering of seeds)
Seeds need to be carried away before they can grow into a new plant. Plants scatter or
disperse their seeds in the following ways:
Dispersal by Wind
Whenever 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.
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Life and Living: The Life Cycle of Plants
Dispersal by Animals
Forgotten acorns buried by squirrels can grown into oak trees. The hooks of the seed of the
grapple plant can catch onto an animals’ fur and are dispersed in this way.
Fruits and berries are eaten by birds and then are excreted in the birds' droppings. The seeds
in the droppings, if pollinated, can grow where it is dropped.
Dispersal by Water
Seeds can also fall into water such as rivers and streams and be dispersed in this way.
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Life and Living: The Life Cycle of Plants
Dispersal with an Explosion
Some seed-pods, like the pea, explode to release their seeds.
Some seeds, like the squirting cucumber, can squirt out fluid containing seeds, when pressed.
Germination
The process that a plant goes through when it starts to grow from a seed is called
germination. Germination will only occur 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.
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Life and Living: The Life Cycle of Plants
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 old
plants. This is known as vegetative reproduction.
Making a Cutting
Cutting in Plant Pot
Plant Growing in Pot
Growth and Maturity
The seedling will grow over a period of time until it reaches maturity. A mature plant may
produce flowers or bear fruits.
Mature Plant
Sources:
Original Creation: Uploader, Siyavula: Connections web site: Continued Existence of
Plants: http://cnx.org/content/m19953/latest/?collection=col10981/latest
Reproduction by Means of Seeds:
http://cnx.org/content/m19956/latest/?collection=col10981/latest
How Seed is Distributed:
http://cnx.org/content/m19957/latest/?collection=col10981/latest
Germination of Seeds: http://cnx.org/content/m19958/latest/?collection=col10981/latest
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