Asexual Reproduction in Plants - Class 7 Notes & Olympiad Questions

Reproduction

a) Reproduction in plants refers to the process through which plants create new individuals, or offspring, to ensure the survival and continuation of their species. It is similar to how humans and animals have babies or give birth.
b) Plants have two main ways of reproducing: sexual reproduction and asexual reproduction.

Asexual Reproduction

a) Asexual reproduction in plants involves only one parent, and it creates new individuals of the same kind.
b) Unlike sexual reproduction, asexual reproduction doesn't require seeds or spores.
c) The offspring produced through asexual reproduction are exact copies, or clones, of the parent plant.
d) No special reproductive cells, called gametes, are involved in this process.

Sexual Reproduction

a) Sexual reproduction in plants involves two parents, a male parent, and a female parent.
b) The male parent produces male reproductive cells called gametes, and the female parent produces female gametes.
c) These gametes join together in a process called fertilisation, resulting in the formation of a zygote.
d) The offspring produced through sexual reproduction are genetically different from both parents. In plants, the flowers play a crucial role as the main reproductive organs involved in sexual reproduction.

In simple terms, asexual reproduction creates identical copies of the parent plant without the involvement of special cells, while sexual reproduction involves the fusion of male and female reproductive cells to create genetically diverse offspring.

Asexual Reproduction in Plants

Modes of Asexual Reproduction

Asexual reproduction in plants occurs through various methods, including fragmentation, spore formation, budding, and vegetative reproduction: 

Fragmentation

a) Fragmentation is a method of asexual reproduction in which the body of the parent plant breaks into distinct pieces, and each of these pieces has the ability to grow into a new offspring or individual plant.
b) An example of a plant that undergoes fragmentation is Spirogyra, which is a type of green algae commonly found in freshwater environments.

Spore Formation

a) Spore formation is a method of asexual reproduction that is observed in plants such as mosses and ferns.
b) Spores are structures covered by a hard protective coat, which helps them withstand unfavourable conditions like extreme temperatures or lack of water. The protective coat allows the spores to remain dormant until they encounter suitable conditions for growth.
c) When the environmental conditions become favourable, such as the presence of moisture and nutrients, the spores germinate. This means they start to grow and develop into new plants.
d) The spores can be dispersed through various means like wind, water, or even by animals. Once they reach a suitable environment they form new plants.

Budding

a) Budding is a method of asexual reproduction in which a bud, along with a portion of the stem from a desired plant, is taken.
b) This bud is then inserted into a small slit made on the bark of another plant. The two plants are tied together. This method is used for reproduction in certain plants like the plum rose.

Vegetative Propagation

a) Vegetative propagation is a type of asexual reproduction in which new plants are formed from vegetative parts of a plant, such as roots, stems, leaves, or buds.
b) These plant parts can detach from the parent plant and give rise to new plants, and they are referred to as vegetative propagules.
c) Vegetative propagation can occur naturally, such as when a plant's stem touches the ground and develops roots, or it can be artificially induced by humans for plant propagation purposes.

1. Natural Vegetative Propagation

In nature, some plants can reproduce without any help from humans, and this is called natural vegetative propagation. Let's look at some examples:

Reproduction From Roots

a) Plants like sweet potatoes have a special part that we eat, called the root or tuber. These tubers have buds called "eyes."
b) When we cut a sweet potato into pieces and plant them in the soil, each piece can grow into a new plant.
c) The buds, or "eyes," on the tuber have the ability to develop into shoots and roots, giving rise to new sweet potato plants. It's like the tuber is a little piece of the parent plant that can grow into a whole new plant.

Reproduction From Stems

a) Reproduction from stems is a method of vegetative propagation found in plants like potatoes, onions, ginger, and turmeric.
b) These plants have underground stems called stem tubers. The stem tubers are swollen and contain nodes or "eyes" with buds.
c) These buds have the ability to grow into new shoots and roots, resulting in the formation of new plants.

Reproduction Through Leaves

a) Some plants, such as bryophyllum and begonia, can reproduce through their leaves.
b) In bryophyllum, notches on the leaves contain buds that have the ability to grow into new plants. When these notched leaves come in contact with the soil, the buds can take root and develop into independent plants.
c) Similarly, fallen leaves of begonia plants also have buds that can grow into new plants when they touch the soil. These buds on the leaves have the potential to sprout roots and shoots, giving rise to new begonia plants.
d) In both cases, leaves play a role in vegetative propagation, allowing these plants to reproduce and produce new offspring without the need for seeds.

2. Artificial vegetative propagation

Artificial vegetative propagation refers to the intentional methods used by humans to create new plants. These techniques involve separating and growing specific parts of a plant to generate new individuals. Here are some common methods:

Reproduction Through Cuttings

a) In this method, a portion of a mature stem from a parent plant is carefully cut and placed in a suitable environment, such as soil or water.
b) Over time, the cut stem develops roots from its lower end and new shoots and leaves from its upper end.
c) The stem essentially transforms into a new plant. This method is commonly used for plants like roses, sugarcane, and many houseplants.

Reproduction by Layering

a) Layering is a method where a branch of a parent plant is bent and partially buried in the soil.
b) Roots develop from the buried portion of the branch, and once a strong root system forms, the branch is separated from the parent and grows into an independent plant.
c) Plants like grapevines, jasmine, lemon, cherry, and croton can be propagated using this technique.

Reproduction by Grafting

a) Grafting involves joining a piece of one plant, called the scion, with the stem of another plant, called the stock.
b) The scion contains desirable traits or characteristics that we want to preserve, while the stock provides a strong and well-established root system.
c) The two parts are carefully connected, allowing them to grow together as a new plant.
d) This method is commonly used in propagating fruit trees, like apples and oranges, and also roses.

Tissue Culture

a) Tissue culture, also known as micropropagation, is a method of artificial vegetative propagation. It involves taking a small piece of plant tissue, such as a leaf or a stem, and growing it in a nutrient-rich medium under controlled environmental conditions.
b) By providing an environment optimized for growth and reproduction, tissue culture provides a reliable and efficient method to produce large numbers of identical plants from a small piece of plant tissue.

Advantages of Vegetative Propagation

a) Preserving Desirable Traits: When we use vegetative propagation, we can make new plants that have the exact same traits as the parent plant.

b) Quick and Reliable: Vegetative propagation is a fast and reliable way to grow new plants. It doesn't rely on seeds, which can take a long time to grow and have uncertain outcomes

c) Early Maturity and Productivity: Plants that are propagated vegetatively often grow and start producing fruits or flowers earlier than plants grown from seeds.

d) Saving Rare and Endangered Plants: Vegetative propagation is also helpful for saving rare or endangered plants. By making new plants that are exactly the same as the rare ones, we can protect and increase their numbers. This is important for preserving biodiversity and ensuring that special plant species don't disappear.