Chlamydomonas
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This ppt explains all about the genus Chlamydomonas.
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Chlamydomonas
- 1. Prepared by: Dr. Sangeeta Das, Assistant Professor, Bahona College, Jorhat, Assam, India CHLAMYDOMONAS
- 3. Occurrence of Chlamydomonas: •Chlamydomonas is a large genus and is found almost in all places. It is represented by about 400 species (Prescott, 1969). •It is mainly found in fresh water rich in nitrogen salts and organic matter. •It is also found in stagnant water of ponds, pools, ditches, water tanks, sewage tanks and in slow running water.
- 4. • Single celled green alga • Grows in ponds, ditches, and wet soil • believed to be primitive • reproduces asexually by producing ZOOSPORES • Reproduces sexually by producing ZYGOTES
- 5. Parts of
- 6. 1.Cell wall: There is a thin cell wall on the outside. It occasionally possesses an outer thin mucilage sheath. It is made up of glycoprotein and non-cellulosic polysaccharides. 2.Flagella: The two flagella situated anteriorly near the pointed. They either project through one aperture in the wall or through two separate canals. These flagella arise form two basal granules called blepharoplast. 3.Contractile vacuoles: Each cell typically possesses two contractile vacuoles at the base of flagella. They have respiratory and excretory functions. 4.Eye spot: It is covered by a minute lens in the thickness of the cell wall. It supposed to function as an extremely primitive eye. This is sensitive to light. Therefore, it directs the movement of the individual.
- 7. 5. Chloroplast: There is a large cup-shaped chloroplast towards the broader end. The chloroplast varies in shape. In C reticulate, g is reticulate. In C. aplina, it is small discoid. 6. Pyrenoid: Pyrenoid is embedded in the chloroplast. Pyrenoid consists of a central protein body surrounded by numerous minute starch grains. 7. Nucleus: All species are uninucleate. A single nucleus lies in the cytoplasm, filling the cup of the chloroplast.
- 8. Reproduction: Both asexual and sexual reproductions occur in Chlamydomonas.
- 9. Asexual reproduction: I. Zoospore formation: During the formation of zoospores the cell becomes quiescent (non-motile). Its flagella are retracted or discarded. The contractile vacuoles disappear. Its protoplast divides longitudinally into two. It is followed by a simultaneous division of each daughter protoplast and sometimes by a third series of division. Each division of the protoplast is preceded by the division of the nucleus into many parts. Thus each cell produces 2-16 pieces. Each piece secretes a wall around it and forms two flagella. Contractile vacuole and pigment spots also soon appear. In this way 2-16 swarmspores or zoospores are formed within the parent cell. The zoospores or swarmspores are liberated by gelatinization or by the rupturing of the patent cell wall. Each of them develops into a new Chlamyclomonas plant.
- 10. 2. Aplanospore formation: Aplanospores are formed under conditions of drought. The zoospores instead of being liberated found up and develop into aplanospores. 3. Palmella stage: This stage is formed under less favourable, but not very dry conditions. In this condition, the ponds are gradually drying up. These cells do not develop flagella. They are embedded in the mucilage formed by the gelatinization of the parent cell wall. In this way, an amorphous colony is formed. All its cells are embedded in a common gelatinous matrix. This stage is known as the palmella stage. It is named so because the older phycologists thought it to be a species of an alga named Palmella. This is however, a temporary phase. Soon all small daughter cells develop flagella and become motile.
- 11. Sexual reproduction: The sexual reproduction may be isogamy to anisogamy and oogamy.
- 12. I. Isogamy: In this case, the fusing pairs of gametes are naked and equal in size. It occurs in C. reinhardi and C. Iongistigma.
- 13. II. Anisogamy: In this case, fusing pairs are similar in shape but different in size. The female cell produces four larger macrogametes. The male cell produces eight smaller microgametes. It occurs in C. monocia, C. Braunii etc.
- 14. III. Oogamy: In this case, the fusing gametes are different both in size and shape. Oogamy occurs in C. corcifera and C. 00gonium. The female call produces a large macrogamete or egg. The male cell functions as antherozoid.
- 17. Use: Chlamydomonas is used as a model organism for research on answering fundamental questions in cell and molecular biology.
- 18. Know More: • ISOGAMY : Literally means “a marriage of equals” • SPOROPHYTE : Diploid individual that produce individual cells called spores (zoospores) • GAMETOPHYTE : Haploid individual that produces gametes • HETEROMORPHIC Generations : Sporophytes and gametophytes are structurally different • ISOMORPHIC Generations : Sporophytes and gametophytes look alike, although they are different in chromosome number.
- 19. THANK YOU