BASIC SCIENCE II: Reproduction in Plants

Reproduction is the process by which mature individuals produce offspring. It is an essential characteristic of all living organisms.

Importance of reproduction

1. Procreation – reproduction sustains the species so that it does not become extinct.
2. Quality improvement- it allows for the mixing of genetic materials leading to variation among individuals in a species. This is seen in sexual reproduction. The variations form basis of adaptability in their habitats.

Modes of Reproduction in Plants

Reproduction in plants can be categorized into two types:

• Asexual Reproduction – The new plants are produced without using the seeds. In this process, generally, the leaves, stems and roots participate in reproduction.
• Sexual Reproduction – The new plants are produced with the help of the seeds of a plant. In this process, the flowers of the plants participate in reproduction.

In higher plants, offspring are packaged in a protective seed, which can be long lived and can disperse the offspring some distance from the parents. In flowering plants (angiosperms), the seed itself is contained inside a fruit, which may protect the developing seeds and aid in their dispersal.

Plants have two kinds of parts:

• Vegetative Parts – These are the parts of the plant that plays a major role in the life cycle of a plant such as preparation of food, transportation of food, water and nutrients etc. For Example, roots, stems and leaves.
• Reproductive Parts – These are the parts of a plant that play a major role in the reproduction process in plants, For Example, flowers, fruits

Shoot – A young plant is often termed as a shoot. Generally, a shoot is regarded as a part of the plant which has stems, leaves and flowers.

Node – It is a part of the stem or branch of a plant from where the leaf arises.

Vegetative Buds – Sometimes buds are present in the leaves that are capable of developing into shoots. These are called Vegetative Buds.

Asexual reproduction in plants

1. Vegetative Propagation

As the name suggests this type of reproduction takes place with the help of the vegetative parts of the plant. Only one parent can produce the identical offspring in vegetative propagation.

Natural means of Vegetative Propagation:

Vegetative Propagation by Roots

• Plants that have tuberous roots, that is, roots which are used as a storage organ in plants participate in vegetative propagation.
• In order to grow new plants, these tuberous roots are sown in the soil.
• There are buds present on the fruits that grow above the ground and a new plant is formed.
• Example: Sweet potato and Irish potato

Runners: Some plants grow along the ground and contain modified stems called Runners. These runners contain buds that can produce roots and stems. Example:  Strawberries

Vegetative Propagation by Leaves

• Some plants have leaves that contain buds that can develop into a new plant. Example: Bryophyllum

Artificial means of Vegetative Propagation

• Cutting – It is a method in which a cutting from a plant is taken and planted. This cutting is a part of the stem or the branch of the plant. Example: Roses, cassava

Grafting – Sometimes two plants are joined together so that both of them can provide the desired characteristics to the new plant. One plant remains rooted in the ground, which is called the Stock, and provides the essential nutrients and water while the other plants’ stem is attached to it. In this way, a new plant develops. Example: Apples

Advantages of Vegetative Propagation

• The plants that are produced with vegetative propagation grow faster than those that are produced with sexual reproduction.
• The plants that reproduce with vegetative reproduction have fruits and flowers ahead of time.
• The plants that are produced have exactly the same characteristics as that of their parents.

2. Budding

• Yeast is an organism that contains a single cell. It is a fungi not a plant.
• It can propagate every few hours if the proper amount of nutrients are available to it.
• As the yeast finds favourable conditions, a small bulb-like projection produces from the yeast called Bud.
• The bud grows gradually and then gets detached from the parent yeast.
• This new cell then grows measures and produces more cells.

Sometimes a chain of buds is formed which leads to the production of a large number of yeasts altogether.

3. Fragmentation

• Algae like Spirogyra generally reproduce by the process of fragmentation in which they divide themselves into multiple parts.
• As soon as the algae find enough water and nutrients, it fragments and grows into new individuals.
• This process continues and algae multiply quickly in a short period of time.

4. Spore Formation

• Some plants contain spores that float in the air and cause asexual reproduction.
• A spore has a hard protective cover which protects it from the unfavourable environmental conditions like temperature and humidity.
• As a result, the spores can travel long distances and survive for a long duration of time.
• As soon as they find favourable conditions such as moisture and nutrients, they germinate and form new plants.
• For Example, Moss and ferns propagate in this way.

Advantages of asexual reproduction
• Retention of useful characteristics/genes/traits
• Offspring establish faster/shorter life cycle
• Better chances of survival because of suitable environment

Disadvantages of asexual reproduction
• Lack of genetic variation
• Lowered resistance to disease
• Loss of hybrid vigor
• Competition for resources due to overcrowding

Sexual Reproduction in Plants

The flowers of a plant are its reproductive organs that participate in the sexual reproduction process.

The pistil consists of three parts:

• Stigma – It is a sticky surface where pollen grains get attached.
• Style – It is a tube-like structure which connects the stigma and the ovary.
• Ovary – It contains eggs in which the female gametes or eggs are formed.

The meaning of the following terms which describe flowers
Hermaphrodite (Bisexual)
• One with both stamen and carpel eg Hibiscus
• Most flowers are hermaphrodite/bisexual

Unisexual

• Have only one of the reproductive organ: carpel or stamen i.e. either male or female flower.

Carpelate

• Also called pistilate
• Contains only carpels hence a female flower

Staminate

• Also called a male flower.
• Contains stamens only.

Dioecious plants

• Have pistilate and staminate flowers on different plants e.g. pawpaw
• The plants are also known as male or female plant.

Monoecius plants

• Have pistilate and staminate on one plant
• However, pistilate and staminate occur at different parts of the plants e.g. maize

Complete flower

• Has all four parts i.e. Calyx, corolla, androecium and gynoecium

Incomplete flower

• Do not have all four parts
• At least one part is missing.

Regular flower: Those that can be divided into two similar halves by any vertical section passing through the centre. this types of flowers are radially symmetrical.

Irregular flower: Can be divided into two equal halves in one particular plane only. such flowers are bilaterrally symmetrical.

Pedicillate flower: Flower with a stalk.

Solitary flower: Those that occur singly while those that grow in cluster make an inflorescence.

Types of ovary

Superior
Ovary occurs above other floral parts on the receptacle.

Inferior (epigynous) ovary
Other floral parts arise above ovary on the receptacle.

How the male gametes reach the female gametes in plants.

• The male and female gametes fuse and form a zygote.
• The male gametes reach the female gametes by the process of pollination.

Pollination is the movement of pollen from the stamens to the stigma, where germination and growth of the pollen tube occur. Most (approximately 96 percent) of all flowering plant species are hermaphroditic (possess both sexual functions within a plant, usually within every flower), and thus an individual can be pollinated by its own pollen or by pollen from another individual.

• The pollen grains have a tough covering which allows them in surviving the different climatic conditions.
• Due to their lightweight, winds and water often carry them away to different plants. Sometimes the pollen grains also get attached to insects which carry them to different flowers.
• This process of transfer of pollen grains from one stigma to another is called Pollination.

Types of pollination

There are two types of pollination:

• Cross-pollination/ Xenogamy: When the pollen grains land on the stigma of a different flower, whether of similar kind or different kind.
• Self-pollination/ Autogamy: When the pollen grains land on the stigma of the same flower.

There are two types of self pollination:

1. Geitonogamy is when pollen is exported using a vector (pollinator or wind) out of one flower but only to another flower on the same plant
2. Autogamy is self-fertilization, especially the self pollination of a flower.

The Fertilization Process

• A zygote is formed as the fusion between the male and female gametes occurs.
• This process of formation of the zygote is called Fertilization.
• Then the zygote develops and turns in an embryo.

How fruits and seeds are formed?

• After the fertilization process, the ovary of the flowers grows and develops into a fruit.
• The remaining parts of the flower fall off.
• The ovules develop and form the seeds of the fruits.
• The embryo is enclosed inside the seeds.
• Some fruits are fleshy and juicy such as mango, apple and orange. Some fruits are hard like almonds and walnuts

Seed dispersal

• The transportation of seeds from the parent plant to different places is called seed dispersal.
• Seed dispersal allows growth of the same kind of plants in different regions.
• This is helpful because it minimizes the competition for food, sunlight, water and minerals among the plants of the same kind in the same area.
• It also allows them to grow in different habitats.

How the dispersal of seeds occurs?

You can ask our super AI Agriculture Teacher below any question of s5 and s6 agriculture and get answers