. Discuss the Following modes of asexual reproduction

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Following modes of asexual reproduction are known to occur in Ulothrix:

1. Zoospores: The zoospores are formed during favourable conditions. All cells are capable to form zoospores except the holdfast.

2. During the formation of zoospores, the protoplast divides mitotically into number of daughter protoplasts by repeated longitudinal divisions. Each develops into a zoospore. Following are the two types of zoospores: 

3. Macrozoospores: They are quadriflagellate, uninucleate and pyriform (pear shaped) with a pointed anterior end and are often fewer in number. Each macrozoospore consists of a pair of contractile vacuole, a single chloroplast with a pyrenoid and almost anteriorly placed stigma. The zoospores resemble morphologically with Chlamydomonas and are liberated from the parent cell through a pore in the lateral wall. They are first liberated in a thin vesicle that soon disappears making zoospores free in the water.

4. After swimming for a short period the zoospores attach by the anterior pointed end on some solid object. They discard their flagella, secrete a cell wall and divide by a transverse division to produce a lower cell and an upper cell. The lower cell develops into a holdfast while the upper cell by repeated transverse divisions forms the filament.

5. Microzoospores: Filaments of U. zonata produce microzoospores that are formed in large number (4 to 32) similar to that of macro zoospores. They are smaller in size, uninucleate, narrowly ovoid with a round posterior end and they may be quadri - or biflagellate. They swim for a longer period for about 2 to 6 days.

After swimming phase, they attach to some solid object by their anterior end. The process of their development into a filament is similar to that of macro zoospores.

Apart from zoospore Ulothrix also reproduces through. 

(i) Aplanospores (ii) Hypnospores (iii) Akinetes (iv) Palmella spores 


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