chlamydomonas-2

chlamydomonas-2 - cell they swim about and may meet other...

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Chlamydomonas 2 Reproduction . In favourable conditions the chlamydomonas individuals will continue to grow and then, at a certain size, reproduce by cell division. The flagella are withdrawn, the cytoplasm shrinks slightly within the cell wall (1), the nucleus and then the cytoplasm divide once, twice, or occasionally three times, to give two, four or eight separate units of cytoplasm each with a nucleus and chloroplast (2). Each of these units forms a new cell wall and a pair of flagella. The parent cell wall bursts open and releases the daughter individuals (3). This fission may occur once a day, so that great numbers of chlamydomonas may appear very rapidly, when they usually make the water look green. Sexual reproduction, of a kind, occurs. Division as described above takes place but produces up to sixteen new individuals which do not develop cell walls. On release from the parental
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Unformatted text preview: cell they swim about and may meet other individuals and fuse in pairs to form a zygote. The zygote eventually rounds off, withdraws the flagella, secretes a thick wall round the cytotoplasm so forming a zygospore which sinks to the bottom of the pond. In this form it may be resistant to extremes of temperature and survive even the drying up of the pond. As a zygospore, too, it may be distributed in dust or mud, and so reach new situations. The cytoplasm in the zygospore will divide, usually into four units, which are released as new chlamydomonas individuals 1 2 3 (a) gametes meet (b) gametes fuse (c) nuclei fuse (d) flagella withdrawn zygote rounds off (e) zygote secretes thick wall to become zygospore Sexual reproduction D.G. Mackean...
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