8Plant Reproduction

1. Plants.

• How many different types of plantscan 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 inwinter? Would there be any flowers?

• What would the trees look like?

LOOK

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 toclass. Answer these questions.• What do plants need to grow? How

should we take care of thegeranium?

Take care of the geranium for a year.Check your answers to the questions.

WHAT DO YOU KNOW?

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1. Types of Plant Reproduction

Types of Plant ReproductionThere are two kinds of plant reproduction: sexualreproduction 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 anexisting plant.

All plants can reproduce by sexual reproduction.Some plants can reproduce by both methods.

Sexual ReproductionFlowers are responsible for sexual reproduction inplants. A male sex cell and a female sex cell uniteinside a flower. The fruit and seeds develop fromthe flower. Later, a new plant develops from a seed.When a plant reproduces by sexual reproduction,there are differences between the parent plantand the offspring plant. For example, the color of their flowers might be different. The fruit of onemight be smaller than the fruit of the other. One might be more resistant to certain illnessesthan the other. Some plants, like ferns, do not have flowers.However, these plants also produce sex cells andare capable of sexual reproduction.

1. How do plants reproduce?

2. How can a new plant growfrom an existing plant?

3. What do flowers do?

Questions

The tuber and flowers of a potato plant.

The bulb and leaves of an onion. The flowers and stolons of astrawberry plant.

stolons

bulb

tuber

Asexual Reproduction The stem or leaves of a plant are involved in asexualreproduction.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 canalso reproduce by sexual reproduction.

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CuttingsCuttings allow us to grow new plantsfrom existing adult plants. To grow aplant from a cutting, first take anexisting plant. Cut off a branch withseveral leaves. When you plant thebranch, roots will grow out of it. Theroots take hold in the soil and thebranch begins to grow and develop.This kind of asexual reproduction doesnot happen naturally. It is a techniquewe use to produce specific plants, likegeraniums and roses.

• Explain what you must do to grow ageranium from a cutting.

• Do plants reproduce from cuttings naturally? Why or why not?

Activities

Complete the sentences.

• Bulbs, tubers and stolons are involved in .

• The potato plant can reproduce by and by .

Flowers are responsible for in .

• involves the sex cells.

• involves stems and leaves.

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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Compare and Analyze

Tulips have flowers and bulbs.

Geranium

sexual reproduction asexual reproduction

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2. Flowers, Fruit and Seeds

The Parts of a FlowerThe flower is the reproductive unit of floweringplants. 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 leavesthat protect the flower before it opens.

• The pistil has three parts: a stigma, a style andan ovary. The ovary produces the female sexcells, called ovules. The style is usually shapedlike a bottle. The tip of the pistil is called thestigma.

• The stamen has two parts: a filament and ananther. The anthers produce pollen. The male sexcells, or sperm, are in the pollen. Flowers usuallyhave several stamens.

1. Describe flowers.

2. Describe seeds.

3. What kinds of fruit and nutsare there?

Questions

The fruit of a strawberryplant.

The fruit of a blueberrybush.

Fleshy Fruits

Nuts

Almond nuts on an almond tree. Chestnut

protectivecasing

nut

Chickpeas

pistil

corolla

stamen

sepalpetal

The Parts of a Flower

calyx

stigma

style

ovary

anther

filament

Seeds

Activities

Read the key words. Look at the pictures. Put the key words in the correct box. Explain what each part of the flower does.

Draw the following fruit with their seeds in your notebook. Complete the tables.

peach, melon, apricot, plum, tomato, cucumber, apple, pear, green pepper

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SeedsSeeds 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 ofsome seeds, such as peas, is very thin. Other seedsare harder, like watermelon seeds. The covering ofsome seeds is hard and thick, like the apricot seed.

FruitsAfter 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.

The Sunflower Is Not a FlowerAlthough the sunflower looks like aflower, it is not a single flower. Asunflower is a group of many flowers.

• Describe a sunflower.What are its flowers like?

• What other plant has flowers ingroups but looks like a singleflower?

Fruit with One Seed Fruit with Several Seeds Seeds with a Thin Covering Seeds with a Thick Covering

Look

special leaves that protect the flowers

flowerspetals

stigma

anthers

A Single Flower

stigma petal anther filament ovary

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3. From Flower to Fruit

PollinationPlants with flowers reproduce sexually. Thishappens when pollen from the stamen reaches thepistil. Pollination is the transfer of pollen from themale 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 stamenof another plant of the same species.The wind and certain animals can transfer pollenfrom one flower to another. • For example, the wind transports the pollen of

wheat flowers. The pollen can reach the flowersof many different wheat plants.

• Some animals and insects, like hummingbirdsand bees, also transport pollen. When bees landon flowers to feed, pollen sticks to their bodies.They then carry the pollen from one flower toanother. Bees pollinate rosemary flowers, for example.

Plants that rely on animals for pollination havebrightly-colored flowers or strong smells to attractthe animals. Other plants have small green flowers,so animals do not notice them. The wind transportsthe pollen of these plants.

1. What is pollination?

2. How are plants fertilized?

3. What do the seeds do?

Questions

The wind pollinates this bulrush.Fertilization of a Pea Plant

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stamenwith pollen

The pollen grains openand the male sex cellsappear.

pollengrains

stigma

stigma

fertilization

The fertilized cellswill turn into seeds.

Parts of theovary will turninto fruit.

petal

ovary

male sex cell

female sex cells

Activities

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 of the

plant.

d) In cross-pollination, the pollen from a flower's stamen falls on the

of a plant.

e) During fertilization, a sex cell and a sex cell unite.

f) Fertilization takes place in the of a flower.

Explain the differences between:

a) pollination and fertilization. c) pollen and male sex cells.b) female sex cells and male sex cells. d) seeds and female sex cells.

Which parts of a flower are involved in fertilization?3

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FertilizationMost plants do not have flowers throughout theyear. They flower during their reproductive season,usually in spring. A mature flower produces sex cells: male sex cells, or sperm, in the anthers andfemale sex cells, or ovules, in the ovary. During reproduction, a female cell unites with amale 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 wherethe male and female sex cells unite.

After fertilization, the fertilized cells become seedsand part of the ovary turns into a fruit.The seeds fall to the ground and germinate. Thisproduces new plants. Some seeds germinate a longway from the plants they come from. This happensbecause the wind or animals transport the seeds.

Traveling FruitThe fruit of a dandelion is very light.Its seed is very small. The seed isattached to a stem with a blossom atthe top. When the wind blows, itcarries the fruit with it. For this reason,dandelion seeds can germinate a longway from the plants they come from.

• Could the fruit be transported bythe wind without its blossom?

• Could it be transported by the windif the seeds were big and heavy?

Look

a lot of fruit

a single fruit

blossom

seedstem

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4. Germination and Growth

GerminationA seed produces a new plant through the process ofgermination. A seed must fall to the ground andhave water to germinate. A bean germinates in various stages. First, the bean becomes buried in the soil. Later, a small rootgrows 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 coldmonths of winter in the soil to be able togerminate in spring.

GrowthA plant grows gradually after germinating. It keepsgrowing until it becomes an adult plant. Someplants, like trees, keep growing throughout their lives.The life span of plants varies a lot. In general, treescan 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 growand mature in summer. Some plants lose theirleaves in autumn. Their branches are bare during winter.

1. What is germination?

2. How does germinationhappen?

3. How long do plants live?

4. How do trees change duringthe year?

Questions

1. The root comes out. 2. The root and the stemgrow.

3. The leaves form. 4. The root and the stemcontinue growing. Theexisting leaves grow.New leaves come out.

Bean Germination

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Trees throughout the YearTrees change throughout the year. For example,trees flower in spring. Reproduction also takes placein spring.The leaves on trees also change. Evergreen treeshave leaves all year long. For example, pine treesare evergreen. Deciduous trees lose their leaves inautumn. For example, apple trees are deciduous.

How Can We Measure the Age of a Tree?

We can calculate how old a tree is bycounting the rings on a cross section ofits trunk. Each ring represents one yearof growth. The rings generally vary incolor and thickness because treegrowth varies from year to year. The longest-living plant is believed tobe a species of pine tree called thebristlecone pine. Some bristleconepines are 4,850 years old. This meansthat they were alive when theEgyptians were building the pyramids.

• Why does the number of rings on atrunk tell us how old the tree is?

• Which live longest, plants oranimals? Discuss.

These plants grow new leaves

in spring.

A lot of plants have lost their leaves by winter.

Activities

Complete the sentences.

Explain how plants change throughout the year. Give examples. 2

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Look and Compare

Growth Rings of a Tree

Stages of Germination

1. A is buried in the soil.

2. The grows .

3. Then, the grows.

4. Finally, the grow.

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GreenhousesWhat Are Greenhouses?

Greenhouses are enclosed areas where wegrow plants. We grow plants for food inmany greenhouses. We also grow plants todecorate the streets and our homes. A lotof the peppers, green beans, tomatoes,roses and tulips that we see in marketsgrow in greenhouses.

Cultivating Plants

In greenhouses, we can control everything thataffects plant reproduction and growth. We cankeep the temperature and humidity at optimumlevels. We can give each plant the water andfertilizer it needs. We can also give the plantssubstances to keep them healthy.Consequently, the plants grow quickly. Theyproduce fruit several times a year.

The Advantages

Growing plants in greenhouses gives us alot of fruit all year long. Not long ago,each fruit had its season. For example, youcould only buy cucumbers in summer.Now you can buy cucumbers at any timeof the year. This is because we grow themin greenhouses.

Describe the greenhouses in the photographs.

• How big are they?• What materials are they made of?• What plants do we grow in them?

What are the advantages of growing plants in greenhouses?

Find out about the greenhouses in your community. What plants grow in them?

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SOCIETY

Monitoring plants in a greenhouse.

We also grow fruit in greenhouses, like these peppers.

We grow decorative plants like geraniums in greenhouses.

Put the sentences in the correct order. Writethem in the table.

The pollen from the stamen sticks to thebat’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 anothercactus flower.The bat flies away from the flower with a lot of pollen on its face.

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Pollination of a Cactus Flower

1.

2.

3.

4.

Animal Pollination

INVESTIGATE

HEALTH EDUCATIONWash Fruit before

You Eat ItYou can eat some fruit, like apples, withthe skin still on. The skin containsnutrients too and is good for your teeth. Before you eat fruit, wash it well toremove dirt and other substances. Thesesubstances can get on the skin of thefruit while the plant is growing. It canalso get on the skin when the fruit istransported or sold.

• 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?

Grapevine

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Look at the pictures. 1

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Test Your Knowledge

Copy and complete the diagram.

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?

Put these stages in the correct order. Complete the diagram.

• Formation of the fruit and seeds. • Development of the plant.• Fertilization. • Appearance of the flowers.

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involves

leaves

for example

involves

these produce

sex cells

Plant Reproduction

2. Pollination.1. 3.

4. 6. 5. Germination.

bulbsfemale

1 2 3