IGNOU LSE 12 2018 - Diagrammatically represent four basic types of life cycles of algae.

Question

Diagrammatically represent four basic types of life cycles of algae.

23 Jan 2018

Answer :

Word Count : 1168

The following points highlight the four main patterns of life cycle in algae. The patterns are: 1. Haplontic Life Cycle 2. Diplontic Life Cycle 3. Diplohaplontic Life Cycle 4. Triphasic Life Cycle.

1. Haplontic Life Cycle:

The plant body is gametophyte (haploid) and sporophyte (diploid) stage is represented only by zygote. The gametophytic plant develops haploid gametes in the gametangium. The fusion between gametes results the formation of zygote, the only diploid stage i.e., sporophytic phase of the life cycle.

The zygote undergoes meiotic division and forms four meiospores. These meiospores develop into haploid plants. The alternation of generations can be interpreted by chromosome number (Fig. 3.19).

Image ignouacademy-com--p-represent-77876

This life cycle is also known as monogenic life cycle. This type of life cycle is found in majority of Chlorophyceae like Chlamydomonas, Ulothrix, Oedogonium, Spirogyra, Chara etc. and all members of Xanthophyceae.

2. Diplontic Life Cycle:

The plant body is sporophyte and develops sex organs. Sex organs produce gametes by meiosis. The gamete only represents the gametophytic stage. The gametes undergo fertilization immediately and form zygote. The zygote does not undergo meiosis and give rise to new sporophytic plant body (Fig. 3.20).

Image ignouacademy-com--p-algae-67006

This type of life cycle is found in majority of the members of Bacillariophyceae, some members of Chlorophyceae like Cladophora glomerata. Fucus and Sargassum of Phaeophyceae also show this type of life cycle.

3. Diplohaplontic Life Cycle:

In this type the haploid and diploid phases are equally prominent and are represented by two distinct vegetative individuals. They differ only in chromosome number and function. The haploid gametophytic plant reproduces by sexual method, while diploid sporophytic plant by asexual process. In this life cycle alternation of two vegetative individuals occurs by sporogenic meiosis and fusion of gametes.

It is of two types:

i. Isomorphic or Homologous Diplohaplontic Type:

In this type both sporophytic and gametophytic plants are morphologically similar and free living. The gametophytic plant (haploid) produces gametes, undergo sexual reproduction and form

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