(a) Describe the processes P, Q and R. (b) Identify the process S. (c) What kind of life cycle does Chlamydomonas exhibit? Justify your answer.

Question

Given below is the diagrammatic haplontic life cycle of Chlamydomonas

Refer the given life cycle and answer the following questions.

(a) Describe the processes P, Q and R. 

(b) Identify the process S. 

(c) What kind of life cycle does Chlamydomonas exhibit? Justify your answer.

Answer 1

(a) : P is oogamy. In oogamy there is a fusion of large food laden, non-flagellated female gamete and smaller motile male gamete. Q is anisogamy. In anisogamy, the fusing gametes are structurally similar but differ in size and behaviour. One of the two gamete is larger called macrogamete or female gamete and the other is smaller, termed microgamete or male gamete. R is isogamy. In isogamy, both the fusing gametes are morphologically and physiologically similar. They may be flagellated or non-flagellated.

(b) S represents zygotic meiosis

(c) Chlamydomonas exhibits haplontic life cycle. This can be explained as follows: The plant body is unicellular and haploid. It gives rise to haploid gametes. Gametes fuse to produce diploid zygote. Meiosis occurs at the time of zygote germination. Zygote is the only diploid phase in its life cycle.