Question

Give a brief account of the life cycle of Chlamydomonas with the labelled diagram.

Answer 1

LIFE CYCLE OF CHLAMYDOMONAS:

• Chlamydomonas is a small, unicellular, motile green alga which includes asexual and sexual reproductions in its life cycle.
• The monoploid vegetative cells of Chlamydomonas reproduce asexually by mitosis and cytokinesis.
• In unfavorable ecological conditions, when nitrogen balance becomes upset, a vegetative cell becomes gametangium to perform sexual reproduction and its protoplast undergoes a series of mitotic divisions to produce 4, 8, 16 or 32 gametes of same size, i.e., isogametes.
• The isogametes are smaller than vegetative cells, but with similar morphology to latter.
• The isogametes of some species, such as Chlamydomonas reinhardi, have two chemically and genetically distinguishable mating types, namely plus (+) and minus (-) mating types.
• Whenever, two isogametes of different mating types (i.e.,+-and-) are collided by chance, they are contacted with each other towards their flagellar ends.
• Both gametes unite and form a diploid, tetra flagellate zygote.
• The zygote soon loses its flagella, develops a thick wall around it and becomes relatively more resistant to unfavorable growth conditions.
• With the return of favorable ecological conditions, zygote undergoes meiosis and produces four haploid, motile zoospores, each of which grows into a vegetative cell.

 

Chlamydomonas:

• It is the green algae which consists of about 150 species of  all unicellular flagellates.
• They are found in stagnant water and on damp soil, in freshwater, seawater and even in snow as snow algae.