Reproduction is the biological process by which new organisms are formed from parent organisms. This process ensures the continuation of a species. For unicellular organisms, reproduction means creating an entirely new individual. But for the multicellular organisms, it also means growing and reproducing. The two main types of reproduction are sexual reproduction and asexual reproduction.
Asexual Reproduction
This type of reproduction involves only one parent, and offspring inherit the genes of that single parent only. Asexual reproduction can be faster and more efficient than sexual reproduction. This type of reproduction process is generally followed by the lower organisms.
1. Budding
Budding is a type of asexual reproduction that results in the formation of a new organism from a growth or bud through cell division at a specific site of the parent's body. The progeny produced is identical, as only one parent is involved and no genetic variations or recombination occur.
Features of budding in yeast are given below:
- A small protrusion appears on the surface of the yeast.
- The bud keeps growing while remaining attached to the parent body.
- A copy of the parent cell's nucleus is transferred to the growing bud along with cell organelles.
- The bud matures with time and grows to the same size as the parent.
- After fully growing, it detaches from the parent, creating two yeast cells.
- Sometimes the newly formed buds remain attached to the parent cell for a long time, and this forms a chain of buds called pseudomycelium.
2. Binary Fission
Binary fission is a form of asexual reproduction commonly found in single-celled organisms. The process starts with DNA replication, ensuring each daughter cell has a complete genetic copy.
Features of Binary fission are given below:
- Binary fission is a form of asexual reproduction commonly found in single-celled organisms.
- The process starts with DNA replication, ensuring each daughter cell has a complete genetic copy.
- The cell elongates, and as DNA replication progresses, cellular components replicate. The duplicated DNA molecules then segregate to opposite cell ends. Finally, the cell divides into two genetically identical daughter cells, each inheriting a full set of genetic material.
- Binary fission in organisms can occur in four ways: irregular, longitudinal, transverse, oblique, that is, left oblique and right oblique.
3. Spore Formation
Spore formation is a special kind of reproduction used by certain organisms to create offspring. Spores are haploid unicellular bodies and are produced as a result of sexual and asexual reproduction.
Features of the Spore formation are given below:
- Spores are tiny, single-celled entities that can either be motile or non-motile.
- Unlike more traditional methods like sexual reproduction, spore formation is the process of creating specialised cells called spores that can develop into new individuals. Large spore-containing sacs are called sporangia.
4. Fragmentation
Fragmentation is a form of asexual reproduction in which the organism’s body breaks into pieces that further develop into new organisms that develop and mature to show the same process of reproduction.
Features of fragmentation in Spirogyra are given below:
- In this process, the organism may break into two or more fragments that will grow into a complete clone. This process is usually seen in favourable conditions with ambient conditions and nutrient availability.
- In Spirogyra, the filamentous thallus is broken into multiple fragments by the dissolution of the middle lamella between cells, which will undergo multiple mitotic divisions that will give rise to new filaments that will mature to form adult filaments.
5. Vegetative propagation
Vegetative propagation is a type of asexual reproduction in which a new plant grows from the vegetative part of the parent plant instead of the reproductive part, i.e., the flower. The produced offspring are vegetative clones of the parent plant, i.e., both the parent and offspring are genetically identical without any variation.
Vegetative Propagation is divided into 2 subtypes:
Natural Vegetative Propagation
In the natural technique of vegetative propagation, the vegetative parts of the plant can be utilised so that the plant can propagate faster. Different types of examples of Natural Vegetative Propagation are shown below:
- It occurs with the help of the vegetative structures of the plant, like the stem, roots, and leaves.
- Roots: Tap roots of Guava, Dalbergia, etc., and adventitious roots of Sweet potato, Dahlia, etc., give rise to adventitious buds that help in their vegetative propagation.
- Leaves: In plants like Adiantum, Bryophyllum, etc., the leaves give rise to the adventitious buds for vegetative propagation.
- Runners: Some plants, including grasses and strawberries, generate horizontal stems (also known as stolons) that rise above the ground. These stems eventually divide into genetically identical plants by producing roots and new shoots at nodes.
- Rhizomes: Plants like Ginger, Bamboo, etc., have modified underground stems that are horizontal, thick, and fleshy, known as rhizomes. These are capable of producing new shoots and roots when they emerge from the soil.
- Suckers: Plants like Chrysanthemum, Mentha, etc., have modified sub-aerial stems that grow horizontally below the soil surface, and their tips directly give rise to a shoot with or without a root.
- Tubers: Plants like Potatoes, etc., have modified underground swollen stems that help in storing food. These stems also have nodes that are called eyes that have buds in them, which give rise to new plants.
- Offsets: Aquatic plants like Eichhornia, Pistia, etc. have modified sub-aerial stem-like runners but with smaller internodes that give rise to a new plant from their nodes.
- Bulbs: Plants like Onions, Tulips, etc. have condensed, modified underground stems with Adventitious roots and fleshy scale-like leaves that store food. A new plant arises from the node present in the stem.
Artificial Vegetative Propagation
When vegetative propagation takes place artificially based on human commercial requirements, it is called Artificial vegetative propagation. The types of artificial vegetative propagation are given below:
Features of artificial vegetative propagation are given below:
- The part of a plant that is used for artificial vegetative propagation is called a vegetative propagule.
- These methods are beneficial to retain desirable traits like flavour, colour, disease resistance, etc.
- Cutting: In plants like Lemon, Orange, etc., a part of the root is cut or excised and planted in a new place to grow a new plant.
- Grafting: In plants like Mango, Guava, etc., the stem system of the desired variety is cut and inserted into the root system of another healthy plant.
- Layering: In plants like Jasmine, Tomatoes, etc., a single stem or multiple stems can be bent and buried in the soil to give rise to a new plant.
- Tissue Culture: It is also called Micropropagation and is done for plants like Bananas, Orchids, etc., in which cells or tissues of a plant are cultivated in a suitable medium in a laboratory from which multiple disease-free plantlets can be produced.
Sexual Reproduction
Sexual reproduction is a process where two parents are involved in the formation of gametes. In this type of reproduction, the offspring receives the genes from both of their parents, which leads to genetic variation.
Steps of sexual reproduction are given below:
1. Pollination
Pollination is the biological process by which pollen from the male part of the flower transfers to the female part of the same or different flowers. Pollination results in fertilisation and the production of seeds. Pollination is important for the reproduction of plants.
Self-Pollination: Self-pollination occurs when pollen grains are transferred from the anther of one flower of a plant to the stigma in the same flower of the same plant.
Features of self-pollination are given below:
- During self-pollination, the eggs and sperm of the same flower share the same genetic information, which leads to a reduction in genetic diversity.
- Less wastage of pollen grains as compared to cross-pollination.
- It ensures a standard harvest quality in vegetable gardening and farming.
- It ensures the elimination of recessive characters.
- It doesn't rely on any pollinators like bees, water, wind, etc. They require less effort than plants as they don't need pollinators.
- It ensures that even a small quantity of pollen produced from plants can achieve a success rate in the population.
Cross-Pollination: Cross-pollination occurs when pollen grains are transferred from the anther of one flower of one plant to the stigma of another flower of another plant.
Features of cross-pollination are given below:
- During cross-pollination, the eggs and sperm will share their different genetic information, which leads to an increase in genetic diversity. While combining the different genetic information, the offspring will become unique.
- Seeds are produced in more significant quantities and have high strength and survivability.
- Genetic recombination during fertilisation causes the hereditary traits in the lineage to disappear.
- Cross-pollination brings about variation in species.
2. Fertilisation
The stigma stores pollen collected by the female reproductive organ, the carpel. Since the fusing within the embryo sac occurs twice, this event is known as double fertilisation.
Features of Fertilisation are given below:
- Double fertilisation is a unique feature of angiosperms; it ensures that the parent plant invests a seed with food storage only if the egg is fertilised.
- Zygote, formed as a result of fertilisation, develops into an embryo, and the embryo develops into a new plant.
- Fertilisation restores diploid conditions by fusion of haploid male gametes and female gametes to produce a zygote (through syngamy).
- Fertilisation also helps to avoid polyembryony.
3. Seed Formation
A seed is formed when a fertilised ovule undergoes mitosis. It stores food and has the potential to grow new plants.
Features of seed formation are given below:
- The zygote is transformed into an embryo, and the ovule gets transferred into a seed.
- The seed is protected by a seed coat, which consists of two layers: that is tegmen and the testa.
- The testa is the outer layer, which is protective in nature, and the tegmen is are inner layer, which is thin in nature.
4. Seed Germination
Seed germination is the process by which a plant grows from a seed. The sprouting of a new plant from a seed constitutes the initial step of plant growth and development.
Features of seed germination are given below:
- The leaves appear, the plant starts to manufacture its own food through photosynthesis and forms a root system to take up nutrients from the soil.
- Water, temperature, light, oxygen, and other environmental elements all play a role in the process of germination.
- In the initial phase of germination, seeds absorb water quickly, causing the seed coat to swell and soften under optimal temperature conditions. This stage is known as imbibition. It initiates the growth process by activating enzymes.
- The seed activates its internal physiological activities, starting respiration, protein synthesis, and metabolising the stored food. This marks the lag phase of seed germination.
- Following the rupture of the seed coat, the radicle emerges to develop into the primary root, initiating the absorption of water from the soil. Once both the radicle and plumule emerge, the shoot initiates its upward growth.
- In the last stage, the cells within the seeds become metabolically active, undergoing elongation and division to facilitate the emergence of the seedling.