Classification and Modes of Plant Reproduction
The process by which the production of new individuals occurs from its parents is termed reproduction. In the case of plants, they undergo the same reproduction process to produce new individuals and it is inherited features that are present in all living organisms. By this process, organisms are able to maintain their races. There are different modes of reproduction that are seen in different animals and the same is with plants also.
Mode of Reproduction in Plants
For determining the genetic constitution of a plant and finding out its characteristic features, knowing the mode of reproduction is necessary. If we carefully see plants we will notice that they consist of different parts where each part performs its specific function. These parts may be categorized into two types one is the vegetative part: leaves, roots and stem and the other is reproductive, which include flowers. So, the major part of plants that perform the reproduction process is flowers. During the process of reproduction in plants, the male parts and the female parts are brought in contact and then fusion of gametes takes place which further produces food that bears seeds. Further these seeds undergo a germination process to give birth to new plants. Along with that some plants also have the capability to give rise to a few plants with the help of their vegetative parts like buds, stem, leaves, etc.
Classification of Mode of Reproduction in Plants
Asexual Mode of Reproduction: In this mode of reproduction, plants give rise to new individuals without any involvement of male and female reproductive parts of plants. In such reproduction, no fruit and seed is seen in plants.
Further asexual reproduction is categorised into different types, they are:
Vegetative Propagation: In this type, new plants are produced from a certain portion of plants. It can be done both with natural process or artificial method. For example, the production of onion bulbs is a natural process whereas rose plants are grown by artificial methods of propagation.
Budding: In this mode, new plants are grown from a bud, which is a kind of outgrowth present in the plant body.
Fragmentation: In this mode of reproduction, new plants are produced from the fragments which are present in the plant body.
Apomixis: It is mode seeds are formed and the development of the embryo takes place without fusion of male and female gametes. One of the common examples of plants that show this mode of reproduction is the Citrus tree.
Sexual Mode of Reproduction: In this mode of reproduction new plants are formed by the development of embryos which is formed by the fusion of male and female gametes. Fruits of such plants bear seeds and further these seeds give rise to new plants.
Sexual Reproduction in Plants
The process of reproduction can be both sexual and asexual but most of the plants undergo a sexual mode of reproduction. The main reproductive part of the plant is flowers i.e. they produce both male and female gametes.
A Complete Flower Mainly Consists Four Parts, They Are
Petals
Sepals
Stamen (Male Reproductive Part)
It is the male reproductive part which is further made up of two parts, they are - anther and filament. Anther is a sac like structure which mainly does the function of production and storage of pollen. Whereas filaments perform the function of giving support to the anther.
Pistil/Carpel
It is a female reproductive part of plants that further comprises three parts they are: stigma, style, ovary. Stigma is known to be the topmost part of the flower, followed by the style which is a long tube that connects the stigma to the ovary. The ovary is a part that contains ovules and it is the part of the plant where the formation of seeds takes place.
Based on the presence or either stamen or pistil or both, we can categories plant into unisexual or bisexual. A bisexual flower is made up of all four parts. Example of bisexual plants is: china rose, rose, etc. Whereas examples of unisexual flowers are papaya, cucumber and many more.
Different Stages in Sexual Reproduction In Plants
There are three crucial steps which plant undergoes during sexual reproduction:
Pollination: It is the process during which there occurs transfer of pollen grain from anther to stigma, among the same flowers or flowers of different plants. Based on this transfer among the same or different plant pollination is of two types i.e. self pollination and cross pollination.
Zygote Formation: After the first step i.e. after the transfer of pollen grains, there occurs transfer of male gamete down through the style of the pistil to the ovary to the place where the fusion of male gamete to female takes place for the formation of zygote.
Fruit and Seed Formation: Once fertilization is over, formed zygote is developed into an embryo. Further ovaries develop into fruit and ovules develop into seeds.
FAQs on Plant Reproductive System: Complete Guide for Students
1. What is the plant reproductive system and what is its primary function?
The plant reproductive system consists of all the parts and processes that enable a plant to create new individuals. Its primary function is to ensure the continuation of the species. This can happen through two main methods: sexual reproduction, which involves the fusion of gametes and typically involves flowers and seeds, and asexual reproduction, which involves a single parent producing genetically identical offspring from its vegetative parts.
2. What are the main reproductive parts of a flower and their functions?
A flower's reproductive parts are organised into whorls. The two most important are:
- The Androecium (Male part): This consists of stamens. Each stamen has an anther, which produces pollen grains (containing male gametes), and a filament, which is the stalk that holds the anther up.
- The Gynoecium (Female part): This is the pistil or carpel. It has three main parts: the stigma, a sticky tip that receives pollen; the style, a tube connecting the stigma to the ovary; and the ovary, which contains ovules that house the female gamete (egg cell).
3. What is the difference between self-pollination and cross-pollination?
The key difference lies in the source of the pollen. In self-pollination, pollen is transferred from the anther to the stigma of the very same flower or another flower on the same plant. In cross-pollination, pollen is transferred from the anther of a flower on one plant to the stigma of a flower on a different plant of the same species. This process introduces genetic variation.
4. How do plants use agents like wind and insects for pollination?
Plants have specific adaptations to use different pollinating agents. Insect-pollinated flowers are often large, brightly coloured, and produce nectar and a sweet scent to attract insects like bees. Their pollen is often sticky to cling to the insect's body. In contrast, wind-pollinated flowers are typically small, dull, and lack nectar or scent. They produce vast amounts of lightweight, non-sticky pollen to increase the chances of it landing on a compatible stigma.
5. What is the key difference between sexual and asexual reproduction in plants?
The primary difference is genetic. Sexual reproduction involves the fusion of male and female gametes, creating offspring with a unique combination of genes from both parents. This results in genetic variation. Asexual reproduction involves only one parent and produces offspring that are genetically identical to the parent, essentially a clone. This happens through methods like budding or vegetative propagation.
6. What are the main stages of sexual reproduction in a flowering plant?
The process follows a clear sequence of events:
- Pollination: The transfer of pollen from the anther to the stigma.
- Pollen Germination: The pollen grain forms a pollen tube that grows down the style towards the ovary.
- Fertilisation: The male gamete travels down the pollen tube and fuses with the female gamete (egg cell) inside the ovule.
- Seed and Fruit Formation: After fertilisation, the ovule develops into a seed, and the surrounding ovary matures into a fruit.
7. Why is cross-pollination often more beneficial for a plant's long-term survival than self-pollination?
Cross-pollination is more beneficial because it promotes genetic diversity. By combining genes from two different parent plants, it creates new variations in the offspring. This genetic variation is crucial for a species' ability to adapt to changing environmental conditions, resist new diseases, and evolve over time. Self-pollination produces genetically uniform offspring, which can be vulnerable if the environment changes.
8. What happens after a pollen grain lands on the stigma? Explain the process of fertilisation.
Once a compatible pollen grain lands on the stigma, it absorbs moisture and nutrients, a process called germination. It then grows a thin tube, known as the pollen tube, which penetrates the stigma and grows down through the style. This tube carries the male gametes. It continues to grow until it reaches an ovule within the ovary. The tip of the pollen tube then releases the male gametes into the ovule, allowing one to fuse with the egg cell, completing the process of fertilisation.
9. What is double fertilisation and why is it significant in angiosperms?
Double fertilisation is a complex process unique to flowering plants (angiosperms). It involves two separate fusion events within the ovule. One male gamete fuses with the egg cell to form the zygote, which develops into the embryo. The second male gamete fuses with the two polar nuclei in the central cell to form the primary endosperm nucleus (PEN). This PEN develops into the endosperm, a nutritive tissue that provides food for the developing embryo. Its significance lies in preventing the plant from wasting resources on nourishing an ovule that has not been successfully fertilised.
10. How are fruits and seeds formed from a flower after fertilisation?
After fertilisation triggers hormonal changes in the flower, the ovary begins to mature and swell, developing into the fruit. The wall of the ovary becomes the fruit wall (pericarp). Simultaneously, the ovules contained within the ovary develop into seeds. The zygote inside each ovule grows into an embryo, which is enclosed within a protective seed coat. Other floral parts, like the petals and sepals, typically wither and fall off as their function is complete.
