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Plant Reproduction
LOOK
1. Plants.
• How many different types of plants
can you see in the photograph?
Describe them.
• How are they different?
• Which of the plants have flowers?
2. This photograph was taken in spring.
Imagine the landscape in winter.
Draw it.
• Would you see the same plants in
winter? Would there be any flowers?
• What would the trees look like?
W H AT D O Y O U K N O W ?
1. Answer the questions.
• Why do we plant seeds?
• What part of a plant contains seeds?
• Is a potato a type of fruit? What
about a tomato?
2. Taking care of a plant.
Bring a geranium in a flowerpot to
class. Answer these questions.
• What do plants need to grow? How
should we take care of the
geranium?
Take care of the geranium for a year.
Check your answers to the questions.
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1. Types of Plant Reproduction
tuber
stolons
bulb
The bulb and leaves of an onion.
The tuber and flowers of a
potato plant.
The flowers and stolons of a
strawberry plant.
Types of Plant Reproduction
There are two kinds of plant reproduction: sexual
reproduction and asexual reproduction.
• The part of the plant responsible for sexual
reproduction is the flower.
• Asexual reproduction occurs when a new
plant grows from the stem or leaves of an
existing plant.
All plants can reproduce by sexual reproduction.
Some plants can reproduce by both methods.
Sexual Reproduction
Questions
1. How do plants reproduce?
2. How can a new plant grow
from an existing plant?
3. What do flowers do?
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Flowers are responsible for sexual reproduction in
plants. A male sex cell and a female sex cell unite
inside a flower. The fruit and seeds develop from
the flower. Later, a new plant develops from a seed.
When a plant reproduces by sexual reproduction,
there are differences between the parent plant
and the offspring plant. For example, the color
of their flowers might be different. The fruit of one
might be smaller than the fruit of the other.
One might be more resistant to certain illnesses
than the other.
Some plants, like ferns, do not have flowers.
However, these plants also produce sex cells and
are capable of sexual reproduction.
Compare and Analyze
Cuttings
Asexual Reproduction
The stem or leaves of a plant are involved in asexual
reproduction.
Tubers, bulbs and stolons are types of stem.
• Tubers are stems in the soil. Buds sprout from the
tubers. The buds produce new plants.
• Bulbs are also underground stems. Bulbs have a
bud inside them. The bud produces a new plant.
• Stolons are stems above the ground. New stolons
produce new plants.
When a plant reproduces by asexual reproduction,
the new plant is identical to the original plant.
Plants that reproduce by asexual reproduction can
also reproduce by sexual reproduction.
Cuttings allow us to grow new plants
from existing adult plants. To grow a
plant from a cutting, first take an
existing plant. Cut off a branch with
several leaves. When you plant the
branch, roots will grow out of it. The
roots take hold in the soil and the
branch begins to grow and develop.
This kind of asexual reproduction does
not happen naturally. It is a technique
we use to produce specific plants, like
geraniums and roses.
Geranium
• Explain what you must do to grow a
geranium from a cutting.
• Do plants reproduce from cuttings
naturally? Why or why not?
Tulips have flowers and bulbs.
Activities
1
Complete the sentences.
sexual reproduction
asexual reproduction
• Bulbs, tubers and stolons are involved in
• The potato plant can reproduce by
Flowers are responsible for in
2
•
involves the sex cells.
•
involves stems and leaves.
.
and by
.
.
Which of the following sentences is correct? Explain.
a) Some plants can reproduce sexually and asexually.
b) If a plant reproduces sexually, it cannot reproduce asexually.
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2. Flowers, Fruit and Seeds
The Parts of a Flower
Fleshy Fruits
corolla
pistil
stamen
stigma
anther
style
filament
ovary
sepal
petal
calyx
The fruit of a strawberry
plant.
The fruit of a blueberry
bush.
Nuts
Seeds
protective
casing
nut
Chickpeas
Almond nuts on an almond tree.
Chestnut
The Parts of a Flower
Questions
1. Describe flowers.
2. Describe seeds.
3. What kinds of fruit and nuts
are there?
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The flower is the reproductive unit of flowering
plants. The parts of a flower include the following:
corolla, calyx, pistil and stamen.
• The corolla is the colorful part of the plant. Petals
form the corolla.
• The calyx is at the bottom of the flower. Sepals
form the calyx. The sepals are small green leaves
that protect the flower before it opens.
• The pistil has three parts: a stigma, a style and
an ovary. The ovary produces the female sex
cells, called ovules. The style is usually shaped
like a bottle. The tip of the pistil is called the
stigma.
• The stamen has two parts: a filament and an
anther. The anthers produce pollen. The male sex
cells, or sperm, are in the pollen. Flowers usually
have several stamens.
Look
Seeds
The Sunflower Is Not a Flower
Seeds form inside fruit. Some fruit, like the peach,
only have one seed. Other fruit, like the apple,
have several.
Seeds have a protective covering. The covering of
some seeds, such as peas, is very thin. Other seeds
are harder, like watermelon seeds. The covering of
some seeds is hard and thick, like the apricot seed.
Although the sunflower looks like a
flower, it is not a single flower. A
sunflower is a group of many flowers.
special leaves that
protect the flowers
Fruits
stigma
After fertilization, part of a flower develops into
a fruit.
• Fleshy fruits accumulate water. Grapes,
cucumbers, apples, oranges, strawberries,
peppers, etc. are all fleshy fruits.
• Nuts do not accumulate water. Acorns,
chestnuts, almonds, peanuts, etc. are all nuts.
anthers
flowers
petals
A Single Flower
• Describe a sunflower.
What are its flowers like?
• What other plant has flowers in
groups but looks like a single
flower?
Activities
1
Read the key words. Look at the pictures. Put the key words in the correct box.
Explain what each part of the flower does.
stigma
2
petal
anther
filament
ovary
Draw the following fruit with their seeds in your notebook.
Complete the tables.
peach, melon, apricot, plum, tomato, cucumber, apple, pear, green pepper
Fruit with One Seed
Fruit with Several Seeds
Seeds with a Thin Covering Seeds with a Thick Covering
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3. From Flower to Fruit
stigma
1
2
petal
pollen
grains
stamen
with pollen
stigma
ovary
The pollen grains open
and the male sex cells
appear.
3
4
fertilization
male sex cell
female sex cells
The wind pollinates this bulrush.
The fertilized cells
will turn into seeds.
Parts of the
ovary will turn
into fruit.
Fertilization of a Pea Plant
Pollination
Questions
1. What is pollination?
2. How are plants fertilized?
3. What do the seeds do?
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Plants with flowers reproduce sexually. This
happens when pollen from the stamen reaches the
pistil. Pollination is the transfer of pollen from the
male part to the female part of flowers.
Some plants self-pollinate. The pollen comes
from the stamens of the same plant. Other plants
cross-pollinate. The pollen comes from the stamen
of another plant of the same species.
The wind and certain animals can transfer pollen
from one flower to another.
• For example, the wind transports the pollen of
wheat flowers. The pollen can reach the flowers
of many different wheat plants.
• Some animals and insects, like hummingbirds
and bees, also transport pollen. When bees land
on flowers to feed, pollen sticks to their bodies.
They then carry the pollen from one flower to
another. Bees pollinate rosemary flowers,
for example.
Plants that rely on animals for pollination have
brightly-colored flowers or strong smells to attract
the animals. Other plants have small green flowers,
so animals do not notice them. The wind transports
the pollen of these plants.
Look
Traveling Fruit
Fertilization
Most plants do not have flowers throughout the
year. They flower during their reproductive season,
usually in spring. A mature flower produces sex
cells: male sex cells, or sperm, in the anthers and
female sex cells, or ovules, in the ovary.
During reproduction, a female cell unites with a
male cell. The reproductive process is as follows:
1. The anther produces a lot of pollen grains.
The pollen grains contain the male sex cells.
2. The pollen grains fall on the stigma.
3. The pollen grains open and the male sex
cells come out. The male sex cells penetrate
the pistil.
4. Fertilization occurs inside the ovary. That is where
the male and female sex cells unite.
After fertilization, the fertilized cells become seeds
and part of the ovary turns into a fruit.
The seeds fall to the ground and germinate. This
produces new plants. Some seeds germinate a long
way from the plants they come from. This happens
because the wind or animals transport the seeds.
The fruit of a dandelion is very light.
Its seed is very small. The seed is
attached to a stem with a blossom at
the top. When the wind blows, it
carries the fruit with it. For this reason,
dandelion seeds can germinate a long
way from the plants they come from.
a lot of fruit
a single fruit
blossom
seed
stem
• Could the fruit be transported by
the wind without its blossom?
• Could it be transported by the wind
if the seeds were big and heavy?
Activities
1
Complete the sentences.
a) Pollination is
b) The
.
and
are involved in pollination.
c) In self-pollination, the pollen from a flower's stamen falls on the
plant.
of the
d) In cross-pollination, the pollen from a flower's stamen falls on the
of a
plant.
e) During fertilization, a
f) Fertilization takes place in the
2
sex cell unite.
of a flower.
Explain the differences between:
a) pollination and fertilization.
b) female sex cells and male sex cells.
3
sex cell and a
c) pollen and male sex cells.
d) seeds and female sex cells.
Which parts of a flower are involved in fertilization?
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4. Germination and Growth
Bean Germination
1. The root comes out.
2. The root and the stem
grow.
3. The leaves form.
4. The root and the stem
continue growing. The
existing leaves grow.
New leaves come out.
Germination
A seed produces a new plant through the process of
germination. A seed must fall to the ground and
have water to germinate.
A bean germinates in various stages. First, the
bean becomes buried in the soil. Later, a small root
grows downward. Then the stem starts to grow.
Finally, the leaves grow.
Some seeds need special conditions to germinate.
For example, some need to spend the cold
months of winter in the soil to be able to
germinate in spring.
Growth
Questions
1. What is germination?
2. How does germination
happen?
3. How long do plants live?
4. How do trees change during
the year?
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A plant grows gradually after germinating. It keeps
growing until it becomes an adult plant. Some
plants, like trees, keep growing throughout their lives.
The life span of plants varies a lot. In general, trees
can live for many years. Other plants, like poppies,
live for only one year.
The seasons of the year affect the life of plants.
Plants flower in spring. Their fruit and seeds grow
and mature in summer. Some plants lose their
leaves in autumn. Their branches are bare
during winter.
Look and Compare
How Can We Measure
the Age of a Tree?
Trees throughout the Year
Trees change throughout the year. For example,
trees flower in spring. Reproduction also takes place
in spring.
The leaves on trees also change. Evergreen trees
have leaves all year long. For example, pine trees
are evergreen. Deciduous trees lose their leaves in
autumn. For example, apple trees are deciduous.
We can calculate how old a tree is by
counting the rings on a cross section of
its trunk. Each ring represents one year
of growth. The rings generally vary in
color and thickness because tree
growth varies from year to year.
The longest-living plant is believed to
be a species of pine tree called the
bristlecone pine. Some bristlecone
pines are 4,850 years old. This means
that they were alive when the
Egyptians were building the pyramids.
A lot of plants have lost
their leaves by winter.
Growth Rings of a Tree
• Why does the number of rings on a
trunk tell us how old the tree is?
• Which live longest, plants or
animals? Discuss.
These plants
grow new leaves
in spring.
Activities
1
Complete the sentences.
Stages of Germination
1. A
2. The
2
is buried in the soil.
grows
3. Then, the
.
4. Finally, the
grows.
grow.
Explain how plants change throughout the year. Give examples.
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SOCIETY
Greenhouses
What Are Greenhouses?
Greenhouses are enclosed areas where we
grow plants. We grow plants for food in
many greenhouses. We also grow plants to
decorate the streets and our homes. A lot
of the peppers, green beans, tomatoes,
roses and tulips that we see in markets
grow in greenhouses.
We grow decorative plants
like geraniums in greenhouses.
Cultivating Plants
In greenhouses, we can control everything that
affects plant reproduction and growth. We can
keep the temperature and humidity at optimum
levels. We can give each plant the water and
fertilizer it needs. We can also give the plants
substances to keep them healthy.
Consequently, the plants grow quickly. They
produce fruit several times a year.
Monitoring plants in a greenhouse.
The Advantages
Growing plants in greenhouses gives us a
lot of fruit all year long. Not long ago,
each fruit had its season. For example, you
could only buy cucumbers in summer.
Now you can buy cucumbers at any time
of the year. This is because we grow them
in greenhouses.
We also grow fruit in greenhouses,
like these peppers.
1
Describe the greenhouses in the photographs.
• How big are they?
• What materials are they made of?
• What plants do we grow in them?
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2
What are the advantages of growing plants in greenhouses?
3
Find out about the greenhouses in your community.
What plants grow in them?
INVESTIGATE
Animal Pollination
1
Look at the pictures.
1
2
2
3
Put the sentences in the correct order. Write
them in the table.
The pollen from the stamen sticks to the
bat’s face.
The bat drinks the nectar of the cactus
flower.
The pollen on the bat’s face comes
into contact with the stigma of another
cactus flower.
The bat flies away from the flower
with a lot of pollen on its face.
HEALTH EDUCATION
4
Pollination of a Cactus Flower
1.
2.
3.
4.
Wash Fruit before
You Eat It
You can eat some fruit, like apples, with
the skin still on. The skin contains
nutrients too and is good for your teeth.
Before you eat fruit, wash it well to
remove dirt and other substances. These
substances can get on the skin of the
fruit while the plant is growing. It can
also get on the skin when the fruit is
transported or sold.
Grapevine
• Why should we wash fruit before eating it?
• Make a list of fruits that we can eat with the skin still on. How do you normally eat fruit?
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Test Your Knowledge
1
Copy and complete the diagram.
Plant Reproduction
involves
involves
leaves
these produce
for example
sex cells
bulbs
2
female
Complete and answer.
a) Copy the pictures. Label the parts.
b) Write these sentences in the correct boxes:
• The pollen grains in the stamen fall on the stigma of the pistil.
• The female sex cells and the male sex cells unite inside the pistil.
• The pollen grains open. The male sex cells appear and move to the inside
of the pistil.
c) What is this process called? What is the result?
1
3
2
Put these stages in the correct order. Complete the diagram.
• Formation of the fruit and seeds.
• Fertilization.
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3
• Development of the plant.
• Appearance of the flowers.
1.
2. Pollination.
3.
6.
5. Germination.
4.