IGNOU LSE 12 2015 - With the help of examples describe the four basic types of life cycles

Question

With the help of examples describe the four basic types of life cycles of algae.

07 Feb 2018

Answer :

Word Count : 758

1. Haplontic type:

This is the simplest and most primitive type of life-cycle. The other patterns of life-cycle have originated from this type. This type is found in all Chlorophyceae except a few. Sometimes this is called Ulothrix or Chlamydomonad type.

In such cases, the somatic phase (plant) is haploid (gametophyte) while the diploid phase (sporophyte) is represented by zygote. During germination, the zygote (2n) divides meiotically producing haploid (n) zoospores, which develop into individual plants.

Here the unicellular (e.g., Chlamydomonas) or filamentous (e.g., Ulothrix, Spirogyra, Oedogonium, Chara, etc.) gametophyte (n) alternates with a one-celled zygote or sporophyte (2n). The haploid filamentous plants are known as haplonts which reproduce asexually by zoospores or aplanospores producing the individuals like parents.

2. Diplontic type:

This pattern is reverse of Haplontic type. In this case,

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