BSc 1st Year Botany Cyanophyta  Sample Model Practice Question Answer Papers

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Index for BSc 1st Year Botany Cyanophyta

Account of Microcystis: Page 1

Structure and methods of reproduction in Oscillatoria: Page 2

BSc 1st Year Botany Cyanophyta Question Answers

Q.1. Give an account of Microcystis.

Ans.1. Microcystis (Gr. micro =small, cystis = bladder) is a fresh water colonial alga. Most species are euplanktonic and are aided by pseudovacuoles. In tropical countries, species of Microcystis multiply so prolifically that they impart a bluish-green colour to the pond water which appears like “pea soup. Some species of Microcystis, like M. aeruginosa, cause water blooms in lakes.

The prolific growth of some species of Microcystis (e.g., M. aeruginosa) in a water body often results in severe depletion of oxygen. This leads to mass mortality of fish and other aquatic animals due to suffocation. Certain species of Microcystis (e.g., M. aeruginosa) produce a toxin, called microcystin, which is highly toxic to fish and aquatic birds. The toxin is also fatal to domesticated animals that drink contaminated water. M. toxica is highly poisonous and is responsible for the death of thousands of sheep and cattles. In humans, some species of Microcystis cause gastric trouble, if they are ingested along with drinking water or during swimming. There are several species of Microcystis which inhibit the growth of bacteria (such as Staphylococcus, Clostridium), zooplanktons and several other algae.

Thallus Structure

The colonies of Microcystis may be round and definite in shape or irregular or sometimes clathrate, depending upon the species. There are hundreds or thousands of small, marble-like cells in each colony. The spherical or elongated cells in a colony float freely in a colourless, homogeneous mucilaginous matrix. They lack individual sheath, and exhibit typical cyanophycean cell structure. Numerous pseudovacuoles are frequently present in a cell.

Reproduction

Microcystis reproduces only vegetatively and sexual reproduction is completely absent. The vegetative propagation takes place either by fission or by fragmentation of the colony. The fission is simple cell division which takes place in all planes.

In M. flos-aquae, nannocytes, the modified endospores are formed by repeated divisions of cell contents.