Question

Write short notes on the following:

(1) Pollination

(2) Regeneration

(3) Germination of seeds

(4) Multiple fission

(5) Importance of variation

Answer 1

(1) Pollination: The process of transfer of pollen grains from anther to stigma for fertilization is known as pollination. It is one of two types - self pollination and cross pollination. If the transfer of pollen takes place in the same flower or to another flower of the same plant, it is known as self pollination. If the transfer of pollen takes place from one flower to the other flower of another plant of the same species, it is known as cross-pollination. This transfer of pollen takes place through different types of agents such as wind, water, insects, birds and animals.

(2) Regeneration: It is a mode of asexual reproduction in multi-cellular organisms. It involves the capacity of an organism to give rise to an entire offspring from a cut body part. It is seen in small invertebrates such as planaria and Hydra. It is carried out by a special type of cells, which proliferate and divide to form large number of cells. These cells then differentiate into different types of cells and tissues in order to produce a new organism.

(3) Germination of seeds: Seed germination is the first step towards the plant growth. The zygote formed after fertilization divides several times to give rise to an embryo. This embryo develops within the ovule, which later develops into the seed. The embryo inside a seed is inactive or remains dormant. It becomes active on the onset of favourable conditions and grows out of the seed coat as a seedling. This process is known as germination. Favourable conditions for germination are moisture, air and temperature.

When a seed germinates, the portion above the cotyledons, which grows into a shoot, is called a plumule. The portion below the cotyledons, which grows into a root, is called a radicle.

(4) Multiple fission: It is a mode of reproduction which is adopted by many unicellular organisms like amoeba under unfavourable conditions. In multiple fission, the organism secretes a thick protective wall or covering around itself, called cyst. Inside the cyst, the nucleus undergoes repeated divisions and results in the formation of many daughter cells. This nuclear division is followed by the division of cytoplasm. Later, on the onset of favourable conditions, the cyst wall breaks up and small newly formed offsprings are released.

(5) Importance of variation: Variations impart stability and increases the chances of survival of the species. It makes the species better−adapted and suited for the continuously changing environment. The main source of variation is sexual reproduction. It is because in sexual reproduction, two individuals with different DNA combine and give rise to a new individual.