Reproduction in Plants | ICSE Class 8 Biology Notes

This note covers how new plants form, the use of roots, stems and leaves, reproduction in simple organisms, growing plants from cells, flower parts, pollen transfer, the joining of reproductive cells, fruit and seed formation, and the spreading of seeds.

What is reproduction, and how do its two main modes differ?

Reproduction is the production of new individuals from their parents. The new individuals are called offspring. Reproduction allows a kind of organism to continue through successive generations, even though individual organisms eventually die.

Most plants have roots, stems and leaves. These are their vegetative parts. After a period of growth, most plants bear flowers, which perform the reproductive function. However, producing a new plant does not necessarily begin with a flower or a seed.

What distinguishes asexual from sexual reproduction?

Asexual reproduction produces new individuals from a single parent without the fusion of reproductive cells. In sexual reproduction, male and female reproductive cells, called gametes, fuse. A cell is a basic structural unit of a living organism. Their fusion is called fertilisation, and the resulting cell is a zygote.

In flowering plants, sexual reproduction leads to seed formation. New plants can also arise without seeds through asexual methods. A plant growing from a potato bud, an undeveloped shoot, and a plant developing from a seed therefore represent different reproductive routes.

Do not equate sexual reproduction with the compulsory involvement of two separate plants. Male and female reproductive structures can occur in the same flower. The essential distinction is whether gametes fuse, rather than whether two different plants are visible.

How do roots, stems and leaves produce new plants?

Vegetative propagation is asexual reproduction in which roots, stems, leaves or buds produce new plants. A bud on a plant contains a short stem surrounded by immature, overlapping leaves. Vegetative buds develop into shoots and can give rise to new plants.

How can a stem cutting grow?

A cutting is a piece removed from a plant, such as a branch of rose or champa, for growing another plant. A node is the region of a stem where a leaf arises. The leaf attachment region can contain a vegetative bud.

1. Take a branch of rose or champa that has a node, and prepare a cutting.
2. Bury the cutting in soil so that it can develop into a new plant.
3. Water the cutting every day and observe its growth.
4. Record the appearance of roots and new leaves, including the time taken for each.

Observe and record the number of days taken for roots and new leaves to appear. Money plant can also be grown in water and observed for new growth.

Which examples show propagation from different parts?

The potato's eyes are scars that may contain buds. To investigate their role, cut potato portions containing an eye, bury them in soil and water regularly. The eye is a bud-bearing region, not a seed.

The drawing shows a leaf bearing small new plants along its margin. The label points to the new plants, linking their position to the buds at the leaf edge.

See Fig. 8.4 in your NCERT textbook

In cacti, parts detached from the main plant body can grow into new plants. These examples show why the reproductive capacity of a plant cannot be judged simply by looking for seeds.

How do artificial propagation and tissue culture help growers?

People use artificial propagation, meaning propagation carried out by human intervention, to multiply plants. Preparing and planting cuttings is one example. A piece of the parent plant is used to establish another plant with its characteristics.

What is the basic tissue culture process?

Tissue culture grows new plants from tissue or cells removed from a plant. A tissue is an organised group of cells within the plant. An artificial medium is the prepared material in which these cells are grown.

1. Remove tissue or separate cells from the growing tip of a plant.
2. Place the cells in an artificial medium. They divide rapidly to form a small cell mass called a callus.
3. Transfer the callus to another medium containing hormones, chemical substances that regulate growth and development, for growth and differentiation.
4. Place the resulting plantlets, or small developing plants, in soil, where they can grow into mature plants.

Differentiation means that cells develop specialised forms and functions. Tissue culture allows many plants to be grown from one parent in disease-free conditions. It is commonly used for ornamental plants, which are grown for decoration.

What are the advantages and limitations?

Plants raised by vegetative propagation can bear flowers and fruits earlier than plants raised from seeds. The new plants are genetically similar enough to the parent to retain its characteristics. Here, genetically similar means similar in inherited information.

Propagation also helps multiply plants that have lost the capacity to produce seeds, such as the banana, orange, rose and jasmine examples. Retaining parental characteristics is useful when the grower wants the same features in the new plants.

The same similarity limits the range of inherited differences produced by the method. It is therefore useful for preserving an existing set of characteristics, rather than for combining characteristics through sexual reproduction.

How do binary fission and budding produce new individuals?

Asexual reproduction includes several different processes. Binary fission is division of one individual into two. In many bacteria and other single-celled organisms, the cell splits into two equal halves, each becoming a new individual.

Single-celled means that the whole organism consists of one cell. Bacteria provide examples of organisms reproducing by fission; they should not be confused with the flowering plants that reproduce using flowers and seeds.

How does a bud form in yeast?

Yeast is a single-celled organism that can be seen under a microscope. In budding, a small bulb-like outgrowth develops from the parent cell. This outgrowth is also called a bud, although it is different from a leafy bud on a plant stem.

1. A small projection appears on the yeast cell and forms a developing bud.
2. The bud gradually increases in size while attached to the parent cell.
3. The bud detaches and becomes a new yeast cell.
4. The new cell grows, matures and can produce further yeast cells by budding.

Sometimes a new bud arises from an existing bud, producing a chain. Yeast can grow and multiply every few hours if sufficient nutrients, the substances needed for growth, are available.

The sequence shows a yeast cell, a developing bud, a new bud and a chain of buds. Arrows connect the stages, and the attached outgrowths are visibly smaller than the parent cell.

See Fig. 8.5 in your NCERT textbook

The contrast is in how the new individual appears. Fission divides the existing individual into two, whereas budding begins with an outgrowth from it. Neither process requires the fusion of male and female gametes.

How do fragmentation and spore formation differ?

Fragmentation occurs when an organism breaks into pieces and the pieces grow into new individuals. Algae are simple organisms that contain the green pigment chlorophyll, used in making food with light, and are largely aquatic, meaning they live in water. Spirogyra is a thread-like alga, or single member of this group, that reproduces by fragmentation.

When water and nutrients are available, algae can grow and multiply rapidly. An alga breaks into two or more fragments, and the fragments grow into new individuals. This can allow the growth to cover a large area in a short time.

What is different about a spore?

A spore is a reproductive body that can develop into a new individual under favourable conditions. In bread mould, called Rhizopus, spores form within rounded structures called sporangia. The singular of sporangia is sporangium.

The thread-like structures forming the body of bread mould are called hyphae; one thread is a hypha. The sporangia contain the spores. Identifying a thread and identifying a spore-bearing structure therefore require different labels.

1. Spores form inside sporangia in the bread mould.
2. Released spores float in air and can travel long distances because they are very light.
3. A hard protective coat helps a spore withstand unfavourable conditions, including high temperature and low humidity, meaning little moisture in the air.
4. Under favourable conditions, a spore germinates, or begins to grow, and develops into a new individual.

The drawing shows upright stalks above a thread-like base. One rounded sporangium is intact and another releases spores. Labels identify the hypha, sporangium and spores.

See Fig. 8.7 in your NCERT textbook

Fragmentation uses pieces of the existing body, while spore formation produces reproductive bodies. Both belong to asexual reproduction in these examples. Mosses and ferns also reproduce by means of spores; spores should not be labelled as seeds.

What are the four whorls of a typical flower?

A whorl is a ring-like arrangement of floral parts. A typical flower has four whorls, arranged successively on the swollen end of its stalk. They are the calyx, corolla, androecium and gynoecium.

Which parts protect and attract?

The calyx is the outermost whorl, made of sepals. Generally, sepals are green and leaf-like and protect the flower in the bud stage. The corolla consists of petals, which are usually brightly coloured to attract insects for pollination.

Pollination transfers pollen grains, structures that produce male gametes, from an anther, the pollen-producing part, to a stigma, the surface that receives pollen. Calyx and corolla are accessory parts of the flower: they assist its functioning, while the two inner whorls contain its reproductive organs.

Which parts produce and receive reproductive cells?

The androecium consists of stamens, the male reproductive parts. Each stamen has a stalk called a filament and an anther, where pollen grains are produced. Pollen grains are structures that produce male gametes.

The gynoecium is the female reproductive whorl, made of one or more carpels. The female structure studied as the pistil has a stigma, the surface receiving pollen; a style, the connecting portion; and an ovary, the enlarged base.

The ovary contains one or more ovules, the structures in which female gametes form and which later develop into seeds. The female gamete is also called the egg cell or ovum.

The stamen drawing labels the anther and filament. The pistil drawings label stigma, style, ovary and ovule, with a cut-open view showing ovules inside the ovary.

See Fig. 8.9 in your NCERT textbook

A unisexual flower has either stamens or pistil, as in corn, papaya and cucumber. A bisexual flower has both, as in mustard, rose and petunia. Male and female unisexual flowers may occur on the same plant or on different plants.

How do self-pollination and cross-pollination differ?

Pollination moves pollen to the surface where the next stages of sexual reproduction can begin. Generally, pollen grains have a tough protective coat that prevents them from drying up. Wind, water and visiting insects can help move pollen between reproductive structures.

Does the pollen remain on the same plant?

In self-pollination, pollen reaches the stigma of the same flower or another flower on the same plant. In cross-pollination, it reaches a flower on a different plant of the same kind.

Check both the flower and the plant when identifying the type. Transfer between two flowers is not enough information by itself: the flowers may belong to one plant or to two separate plants.

A bisexual flower contains both reproductive parts, but that description alone does not identify the actual route taken by its pollen. Flower type describes the structures present; pollination type describes the transfer that occurs.

Note: Pollination is pollen transfer, not fusion of gametes. The pollen grain reaches the stigma, whereas fertilisation involves the male and female gametes and occurs later in the ovule.

How are flowers suited to insect, wind and water pollination?

An agent of pollination is something that carries pollen to a stigma. Flower and pollen features help explain how an agent works. Wind and water are non-living agents; insects are living agents.

Which features help insect pollination?

The majority of insect-pollinated flowers are large, colourful, fragrant and rich in nectar, a floral food reward. Colour and fragrance attract visitors. Small flowers may be clustered into an inflorescence, a group of flowers, to make them conspicuous.

Pollen grains are generally sticky in animal-pollinated flowers. When a visiting insect touches anthers, pollen coats its body. Contact with a stigma can then transfer pollen. Bees and butterflies are familiar pollinating agents; Yucca provides an example of a plant pollinated by a moth.

The useful features to connect are attraction by colour or fragrance, provision of nectar or pollen as rewards, and pollen that adheres to the visitor. A visit alone does not establish pollination unless the visitor makes the relevant contact.

Which features help wind pollination?

Wind-pollinated plants have light, non-sticky pollen that wind currents can carry. They often possess well-exposed stamens and large, often-feathery stigmas. Exposed stamens help release pollen, while the stigma's form helps trap airborne pollen.

Wind pollination is quite common in grasses. Corn is a familiar example. Wind-pollinated flowers produce enormous amounts of pollen relative to the number of ovules, compensating for the chance nature of pollen reaching a stigma.

Which features help water pollination?

Water pollination is quite rare in flowering plants. Examples include Vallisneria and Hydrilla in fresh water and Zostera among marine seagrasses. Water currents transport the pollen.

Wind- and water-pollinated flowers are not very colourful and do not produce nectar. In most water-pollinated species, a mucilaginous covering, a slimy protective layer, prevents pollen from becoming wet. These features distinguish them from flowers that attract insects with conspicuous displays and rewards.

In Vallisneria, female flowers reach the water surface on long stalks. Male flowers or pollen are released at the surface and carried by currents. In seagrasses, female flowers remain submerged; pollen grains in many such species are long and ribbon-like.

Do not assume that every aquatic plant uses water for pollination. In a majority of aquatic plants, such as water hyacinth and water lily, flowers emerge above water and are pollinated by insects or wind.

How is artificial pollination carried out?

Artificial pollination is pollen transfer deliberately carried out by people. A grower can use pollen from a selected parent and protect the receiving flower from unwanted pollen. This helps control which pollen reaches the stigma.

Why are emasculation and bagging used?

Emasculation means removing anthers from a flower bud before they release pollen. It is used when the chosen female parent has bisexual flowers. Bagging means covering the flower to prevent unwanted pollen from reaching its stigma.

1. For a bisexual flower chosen as the female parent, remove its anthers before they release pollen.
2. Cover the flower with a suitable bag to protect the stigma from unwanted pollen.
3. When the stigma is receptive, meaning ready to receive suitable pollen, dust it with mature pollen collected from the chosen male parent.
4. Cover the flower again and allow the fruit to develop.

If the chosen female flower is unisexual, it has no anthers to remove. It is bagged before opening, pollinated when its stigma is receptive, and covered again afterwards.

Artificial pollination remains part of sexual reproduction because it transfers pollen for the later fusion of gametes. It is different from artificial vegetative propagation, which multiplies plants using their vegetative parts.

What happens between pollination and fertilisation?

After a pollen grain reaches a suitable stigma, a tube grows out from it. This pollen tube grows through the style towards the ovary and carries the male gamete towards the female gamete in the ovule.

What is the correct sequence?

1. Pollination places a pollen grain on a suitable stigma.
2. The pollen grain germinates, producing a pollen tube that grows through the style.
3. The male gamete reaches the female gamete in the ovule.
4. The two gametes fuse during fertilisation and form a zygote.
5. The zygote divides and develops into an embryo, the developing young plant within the seed.

Two drawings show a germinating pollen grain and a pollen tube extending into the pistil. Labels identify the ovum and the site of zygote formation in the enlarged lower region.

See Fig. 8.11 in your NCERT textbook

Keep the structures and cells separate in an explanation. The pollen grain produces the male gamete; it is not itself the male gamete. Similarly, the ovule contains the female gamete, rather than being another name for that cell.

The stigma receives pollen, the style provides the route for tube growth, and the ovary contains the ovules. These connected roles explain why pollen landing on a stigma and gametes fusing in an ovule are distinct stages.

Fertilisation produces a cell, the zygote. The embryo develops from that cell through division. Neither the whole ovary nor the whole ovule should be called the zygote.

How do the flower's parts change into fruits and seeds?

Following fertilisation, several linked changes take place. The zygote develops into an embryo, the ovule develops into a seed, and the ovary grows into a fruit. These are three different relationships, involving structures at different levels.

What develops from each structure?

The seed has a protective seed coat surrounding the embryo. The ovule develops a tough coat as it becomes a seed. The petals, sepals, stamens, style and stigma may shrivel and fall off as the fruit develops.

Fruits differ in their texture. Some, such as mango and orange, are fleshy and juicy. A fruit's role in the reproductive sequence is not determined by whether people treat it as a sweet food.

How does a seed begin the next generation?

Seed germination is the development of the embryo into a seedling under appropriate conditions. A seedling is a young plant growing from a seed. The embryo's root and shoot develop as germination begins.

Thus, fertilisation, seed formation and germination are connected but distinct processes. Fertilisation forms the zygote; seed formation encloses the developing embryo; germination begins the growth of that embryo into a new plant.

Why are seeds dispersed, and how are they carried away?

Seed dispersal is the spreading of seeds to different places. If all seeds fell and grew at the same place, they would face severe competition for sunlight, water, minerals and space. Dispersal also enables plants to reach new habitats, or places where they can live.

Which features match each method?

Seeds or fruits dispersed by water usually develop floating ability through a spongy or fibrous outer coat. Seeds dispersed on animal bodies can have spines and hooks that help them attach and travel to distant places.

Some fruits burst with sudden jerks, scattering their seeds away from the parent. This differs from wind or water dispersal because the fruit's bursting provides the immediate movement.

Note: Pollination transfers pollen to a stigma before fertilisation. Seed dispersal moves seeds or seed-bearing fruits to new places after seeds have formed. Wind and water may help both processes, but they carry different material.

When identifying a dispersal method, connect the visible feature to its function: wings or hairs assist wind transport, floating structures assist water transport, and hooks assist attachment to animals. Keep the seed or fruit distinct from the pollen grain.

Glossary

• Reproduction — The production of new individuals from parents, allowing their kind to continue through successive generations.
• Asexual reproduction — Reproduction from a single parent without the fusion of male and female reproductive cells.
• Vegetative propagation — Asexual reproduction in which new plants arise from roots, stems, leaves or buds of the parent.
• Binary fission — Division of a single parent organism into two individuals, as in many bacteria.
• Budding — Formation of a new individual from an outgrowth that develops on the parent organism.
• Fragmentation — Reproduction in which the body breaks into pieces that grow into new individuals.
• Spore — A reproductive body that can develop into a new individual when conditions are favourable.
• Tissue culture — A method of growing new plants from plant tissue or cells in an artificial medium.
• Pollination — Transfer of pollen grains from an anther to the stigma of a flower.
• Self-pollination — Pollen transfer to the stigma of the same flower or another flower on the same plant.
• Cross-pollination — Pollen transfer to a flower on a different plant of the same kind.
• Fertilisation — Fusion of the male and female gametes to form a cell called the zygote.
• Ovule — A structure within the ovary containing the female gamete and developing into a seed after fertilisation.
• Embryo — The developing young plant formed from the zygote and enclosed within the seed.
• Seed dispersal — The movement of seeds to different places, helping reduce competition and extend plant distribution.

Common errors and misconceptions

• Misconception: Every new plant must grow from a seed. Correct: Vegetative propagation produces new plants from roots, stems, leaves or buds without seed formation.
• Misconception: A potato eye is a seed. Correct: An eye is a scar that may contain a bud capable of developing into a new plant.
• Misconception: Pollination and fertilisation name the same event. Correct: Pollination transfers pollen to a stigma; fertilisation fuses male and female gametes to form a zygote.
• Misconception: Pollen transfer between any two flowers is cross-pollination. Correct: Transfer between flowers on the same plant is self-pollination; cross-pollination involves different plants of the same kind.
• Misconception: The pollen grain is the male gamete and the ovule is the female gamete. Correct: Pollen produces male gametes, while the female gamete forms inside an ovule.
• Misconception: Every plant living in water is pollinated by water. Correct: Water hyacinth and water lily have flowers above water and are pollinated by insects or wind.
• Misconception: The ovary becomes a seed and the ovule becomes a fruit. Correct: The ovary develops into the fruit, while the ovule develops into the seed.
• Misconception: Artificial pollination is a form of vegetative propagation. Correct: It transfers pollen for sexual reproduction; vegetative propagation uses vegetative plant parts.

Exam-style questions with model answers

Q1. A Bryophyllum leaf has buds along its margin. After the leaf falls on moist soil, its buds develop into new plants. Name the reproductive method and explain why this is asexual reproduction. [2 marks]

1. The method is vegetative propagation through buds at the leaf margin.
2. It is asexual reproduction because one parent produces the new plants from a vegetative part without the fusion of gametes.

Q2. In yeast, a small outgrowth appears on the parent cell, enlarges, detaches and becomes a new cell that can reproduce again. Name this method and explain its development in three points. [3 marks]

1. The method is budding. It begins when a small bulb-like outgrowth, called a bud, appears on the parent yeast cell.
2. The developing bud gradually grows in size while attached to the parent and then detaches to form a separate yeast cell.
3. The new yeast cell grows and matures. It can then produce further yeast cells through the same process of budding.

Q3. Compare self-pollination and cross-pollination. Include their shared transfer route, the same-flower case, the same-plant case and the different-plant case. [4 marks]

1. Both processes transfer pollen grains from an anther to a stigma. Neither term describes the fusion of male and female gametes.
2. When pollen reaches the stigma of the same flower, the transfer is self-pollination.
3. When pollen reaches another flower on the same plant, the transfer is also self-pollination.
4. When pollen reaches a flower on a different plant of the same kind, the transfer is cross-pollination.

Q4. Explain the sequence from a pollen grain arriving on a suitable stigma to the development of an embryo. Give five separate stages, identifying the structures involved. [5 marks]

1. Pollination places the pollen grain on a suitable stigma, the pollen-receiving part of the pistil.
2. The pollen grain germinates and produces a pollen tube, which grows down through the style towards the ovary.
3. The male gamete reaches the female gamete, or egg cell, inside an ovule contained in the ovary.
4. The male and female gametes fuse. This event is fertilisation, and the cell it produces is called the zygote.
5. The zygote divides several times and develops into an embryo within the ovule. The embryo is the developing young plant.

Q5. A grower wants to pollinate a bisexual flower with pollen from a selected male parent while excluding unwanted pollen. Describe the use of anther removal, protection, timing, pollen transfer and protection afterwards. [5 marks]

1. Remove the anthers from the selected bisexual flower bud before they release pollen. This step is called emasculation.
2. Cover the flower with a suitable bag. Bagging protects its stigma from contamination by unwanted pollen grains.
3. Wait until the stigma is receptive, meaning that it is ready to receive suitable pollen for the next reproductive stages.
4. Collect mature pollen from the anthers of the selected male parent and dust that pollen onto the receptive stigma.
5. Cover the pollinated flower again and allow the fruit to develop. Rebagging maintains protection after the chosen pollen has been applied.

Q6. Describe four stages of tissue culture, beginning with cells from a growing plant tip and ending with plants growing in soil. Include the terms callus and differentiation. [4 marks]

1. Remove tissue or separate cells from the growing tip of the chosen parent plant.
2. Place the cells in an artificial medium, where rapid division produces a small group of cells called a callus.
3. Transfer the callus to another medium containing hormones for growth and differentiation, the development of specialised cells and structures.
4. Place the resulting plantlets in soil so that they can grow into mature plants.

Q7. A wind-pollinated flower has light, non-sticky pollen, well-exposed stamens and a large feathery stigma. Explain how each of these three stated features helps pollination. [3 marks]

1. The light, non-sticky pollen can be transported by wind currents, allowing it to move away from the flower that produced it.
2. The well-exposed stamens place the pollen where it can be dispersed readily into the moving air.
3. The large feathery stigma helps trap airborne pollen grains, allowing pollen carried by wind to reach the receiving surface.

Q8. A coconut has a fibrous outer coat that helps it float. Xanthium has hooked structures that attach to animal bodies. Identify the dispersal agent in each case and relate it to the stated feature. [2 marks]

1. Water disperses coconut because its fibrous outer coat helps it float and be carried away.
2. Animals disperse Xanthium because its hooked structures attach to their bodies and travel with them.

Key takeaways

• Asexual reproduction produces new individuals from one parent, while sexual reproduction involves the fusion of male and female gametes.
• Vegetative propagation uses roots, stems, leaves or buds; potato eyes and Bryophyllum leaf buds are important examples.
• Fission, budding, fragmentation and spore formation are different reproductive methods, identified by how new individuals arise.
• Tissue culture grows new plants from cells or tissue through artificial media, callus formation and plantlet development.
• A typical flower has calyx, corolla, androecium and gynoecium; stamens produce pollen and the stigma receives it.
• Self-pollination stays within the same plant, whereas cross-pollination transfers pollen between different plants of the same kind.
• Pollination precedes fertilisation: a pollen tube grows, male and female gametes fuse, and the zygote develops into an embryo.
• The ovule develops into a seed and the ovary into a fruit; dispersal helps plants reach new places.

Test yourself

What makes a stem region a node?

A node is the region of the stem or branch at which a leaf arises.

How is fragmentation different from budding?

Fragmentation produces new individuals from pieces of an existing body. Budding begins with a small outgrowth from the parent.

What protects a spore during unfavourable conditions?

A hard protective coat helps a spore withstand conditions such as high temperature and low humidity.

Which floral whorls contain the reproductive organs?

The androecium contains the stamens, and the gynoecium forms the female reproductive whorl of the flower.

Is pollen transfer between flowers of the same plant self-pollination or cross-pollination?

It is self-pollination because the pollen remains within the same plant, even though two flowers are involved.

Why does a unisexual female flower not need emasculation?

It has no stamens or anthers, so there are no anthers to remove before applying selected pollen.

What is the difference between an ovule and an ovary?

An ovule lies inside the ovary and develops into a seed. The ovary contains ovules and develops into a fruit.

How does seed dispersal differ from pollination?

Seed dispersal moves seeds or seed-bearing fruits to new places. Pollination transfers pollen grains from anthers to stigmas.