Question

In Chlamydomonas, the term hologamy is applied to a mode of sexual reproduction in which
A. Gametes are motile.
B. Gametes are holozoic.
C. The young unicellular thalli directly behave as gametes.
D. The gametes are differentiated into male and female.

Answer 1

Hint: Hologamy is a kind of sexual reproduction that involves the fusion of two similar organisms. In hologamy, two organisms act as two gametes. Hologamy also involves genetic recombination that further leads to the variations.

Complete Answer:
- Chlamydomonas is a kind of algae that reproduces by asexual as well as sexual mode of reproduction.
- During the asexual reproduction different types of spores are produced. Spores are released from the parent body which, on germination give rise to new plants. The most common spores produced are the zoospores. They are flagellated (motile) spores and germination gives rise to new plants.
- Sex organs are non-jacketed and unicellular. Sexual reproduction takes place through the fusion of two gametes

Now let us gather information about given options :
1. Gametes are motile: Fusion between two gametes in which both the gametes are motile, that is they are flagellated and move and also they are similar in size is known as isogamous reproduction and occurs in chlamydomonas.
2. Gametes are holozoic: The holozoic gametes means dissimilar gametes , when these kind of gametes fuse with each other it is known as anisogamous reproduction. This usually takes place in chlamydomonas.
3. The young unicellular thalli directly behave as gametes: This type of reproduction is termed as hologamy in which directly the young thallus behaves as gamete and helps in the fertilization. The male and female gamete resembles the somatic cell in these. This occurs in chlamydomonas.
4. The gametes are differentiated into male and female: When gametes are differentiated into male and female gamete that is male gamete is small and motile and female gamete is large and non motile and reproduction is called as oogamous reproduction. This is seen in volvox.

Our required option is C that is The young unicellular thalli directly behave as gametes.

Note: Chlamydomonas possess a haplontic life cycle. The dominant phase in the life cycle is a free-living photosynthetic haploid gametophyte. The diploid or sporophytic generation is represented only by the single-celled zygote. The zygote undergoes meiosis (zygotic meiosis) and forms haploid spores. The spores on germination give rise to gametophyte.