Cyanophyta
Micocystis
Q.1. Describe the life cycle of Microcystis.
Related Question -
Q. Describe the thallus structure of microcystis. (2012)
Q. Describe the reproductive methods of microcystis.
Ans. Systematic position: -
Class - Cyanophyceae
Order - Chroococcales
Family - Chroococcaceae
Occurrence: - Microcystis (Gr. micro = small, kystis = bladder) is a fresh water colonial algae. Most of the species are euplanktonic. They are aided by pseudovacuoles. In tropical countries, species of Microcystis miltiply so prolifically that they impart a bluish-green colour to the pond water which apears like ‘pea soup’ Some species of Microcystis, like M. aeruginosa, become the casuse of water blooms in lakes.
Fig. - Microcystis : A. A colony, B. A part of the colony
The fertile 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 which is known as microcystin. It is highly toxic for this and aquatic birds. This toxin is also fatal for domestic animals that drink contaminated water. M. toxica is highly venomous and it is responsible for the death of thousand of sheep and cattles. In human beings some species of Microcystic casuse 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), zooplanktones and several other algae.
Thallus structure: - The colonies of microcystis may be round and definite in shape or irregular or sometimes uneven, depending upon the species. There are hundreds or thousands of small, marble-like cells in each colony. The spherical or elongated mucilagenous matrix. They lack individual sheath, and show typical cyanophycean cell structure. Numerous pseudovacuoles are frequently presesnt in a cell.
Reproduction: - Microcystis reproduce only vegetatively. Sexual reprpoduction is completely absent in it. The vegetative propagation takes place either by fission or by fragmentation of the colony. The fisson is simple cell division which takes place in all planes.
In M. flos-aquae, nannocytes, the modified endospores are formed by repeted divisions of cell contents.
Oscillatoria
Q.2. Describe the structure and reproduction of Oscillatoria.
Related Questions -
Q. Write short notes on the following.
(i) Oscillating movement
(ii) Cell structure of Oscillatoria (2013)
(iii) Hormogonia
Q. Describe methods of reproduction in Oscillatoria. (2009)
Q. Describe the asexual reproduction in Oscillatoria. (2005)
Ans. Systematic position: -
Division - Cyanophyta
Class - Canaophyceae
Order - Nostocales
Family - Oscillatoriaceae
Genus - Oscillatoria
Occurrence: - The species Oscillatoria are found in fresh water. All the species are aquatic and occur in a wide range of habitates. The algae commonly occur in dirty stagnant and pollutedater, and it also occur on moist rocks, damp soils, temprary water pools, ditches, drains, streams and muddy banks of rivers
Indian species: - Oscillatoria annae, O. chlorina, O. formosa, O. decolarata, O. sancta.
Vegetative structure: - The oscillatoria plant body is filamentous. It made of long thread like filament structures called trichomes. The trichomes occurs singly or a large number of them are interwaven to form flat stratum or spongysheets. Each trichome is long or short, uniseriate, thein, usually strait and unbranched. It is septate and multicelluar. Usually, sheath around the trichome is absent. All the cell are similar and undifferentiated except the teminal one which may be conical, convex, rounded, pointed, bent or coiled.
Cell structure: - The Internal structure of cell is typical cyanophycean. It has an other some what rigid cell all. The cell is not surrounded by mucilaginous sheath. The cell wall encloses protoplasm which is differentiated into two regions. The outer coloured chromoplasm and centeralhyalie centroplasm. The chromoplasm is surround by two layered plasma memberane. There are no plastids, mitochondria, endoplasmic reticulum and dictyosome. This region is colored because of the presence of the pigments located in sac like thylakoids. The thylakoids are not arranged in definite grana or not enclosed with in plastids. The reserve food material is cyanophycaen starch. The central hyaline region is considered as the incipient nucleus.
Growth : - The Growth of trichome is intercalary and occurs by cell divisions.
Movement: - The trichome of Oscillatoria show the characteristic spontaneous movements. These movements may be gliding, Oscillatory or bending. Gliding movements help trichome to glide forwards and back-wards. During oscillatory movements the terminalend of trichome oscillates in pendulum like some what jerky movements.
Chromatic adaptation: - Due to the presence of chlorophyll, c-phyecyanin, c-phyeoerythrin pigments the algae changes its coloured according to the wavelength of incident light. This phenomenon is called chromatic adaptation.
Reproduction: - Only vegetative type of reproduction have been found in osciltatoria.
Fragmentation: - When the trichomes break into two or more pieces due to mechanical injury. Each piece develop into new plant.
Hormogone: - These are short, few celled naked pieces of trichome, delimited by the formation of filaments biconcave dead discs of intercellular substances in the main trichome during the formation of it an intercalary cell of trichome colapse. Its protoplasmes becomes transparant and the cell becomes dead. This cell loses its turgor so that the walls of adjacent cells press towards it. The dead cell now becomes biconcave due to this pressure. Finally the trichome break due to mechanical jerks, separating a short few celled hormogonium. It develops into new plant.
Q.3. In which class you will place the minute plant which lacks mitochondria, chloroplasts, true nucleous but contain to 70S ribosomes and photosynthetic pigment chloophyll-a, carotene and xanthophyll with phycocyanine ? (2005, 10)
Ans. The minute plant which lacks mitochondria, chloroplasts, true nucles but contain 70S ribosome and photosynthetic pigment chlorophyll-a carotene and xanthophyll with phycocyanin will include in class Myophyceae or Cyanophyceae. It is the class of phylum cyanobacteria.
Q.4. Draw neat and labelled diagram of Heterocyst as seen erlectron microscope.
Related Question -
Q. Write a brief note on heterocyst. (2005, 07, 10)
Q. Show the heterocyst and akinetes in Nostoc and explain the utility. (2009, 11)
Ans. Heterocyst: - These are specialized structures found in the members of Nostocales (except Oscillatoriaceae) and Stigonematales. These are specialized large, hyline cells and may be intercalary or basal in position. They are round or barrel shaped. The outer wall of heterocyst is brownish-yellow and
thick. Two polar nodules are present at the both ends of heterocyst. Cytoplasm is dense, homogenous and colourless. Although photosynthetic lamellae are found, but due to absence of phycobillin and chlorophyll pigments, the process of photosynthesis does not occur. Heterocyst consists of glycoliupid and acyl lipids. It also contains specific enzyme nitrogennase.
Utility: - According Fay. et.al heterocysts are the organ of nitrogen fixation. In this process atmospheric nitrogen is converted into ammonia compounds and then utilized. For this process nitrogenase enzyme is essential which is active in the absence of oxygen. Heterocyst consist of a unique type of cell wall, which prevents the entery of oxygen, as a result the conversion of atmospheric nitrogen into ammonia by nitrgenase enzyme taking place continue.
Akinities: -
In several filamentous blue gree algae (Nostoc), certain vegetative cells accumulate food, enlarge in size, turn yello or dark brown in colour and develop a thick wall. These are called akinetes. Akinetes are found isolated away or next to heterocysts or some times in chain (groups).
Akinete resists a long period of drought and can germinate on the return of favourable conditions. Bristol (1920) recorded the akinete germination from dried sample of soil stored for 70 years.