Question

What do you understand by the term alternation of generation? Explain with any one pattern of plant life cycle?

Answer 1

Hint: Alternation of generation refers to the occurrence of diploid and haploid multicellular organisms, giving rise to new organisms. This process allows for both the dynamic and volatile action of sexual reproduction as well as consistence act of asexual reproduction. It is most commonly found in plants and algae.

Complete step by step answer: Life cycle of plants is known as alternation of generation. In plants both diploid and haploid cells can divide by the process of mitosis which leads to the formation of other plant bodies i.e. gametophyte (haploid plant) and sporophyte (diploid plant). It is also known as metagenesis. There are mainly three patterns of life cycle-
Haplontic
Diplo-haplontic
Diplontic.
Haplontic pattern is most commonly seen in green algae for e.g. Chlamydomonas, Ulothrix, and Spirogyra. In the haplontic life cycle, the plant body is gametophyte and independent. The plant body of sporophyte is dependent on gametophyte and there are no free sporophytes. There are two phases in a cycle first is diplophase and second is haplophase. Gametophyte is the dominant one. In diplophase diploid zygotes undergo meiosis division and produce haploid spores. In haplophase these spores again give rise to haploid gametophyte and complete the cycle.

GAMETOPHYTE (n) $\to$ ZYGOTE (2n) $\to$ SPORES (n) $\to$ GAMETOPHYTE (n)

Note: Alternation of the generation process commonly found in plants where plants undergo cell division to produce new organisms. The sporophyte may not always depend on the other generation. But in some cases it is found to be dependent.