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In this article we will discuss about the external morphology of chlamydomonas. Also learn about its Neuromotor Apparatus, Electron Micrograph, Palmella-Stage with suitable diagram.
1. The organism is an unicellular alga (Fig. 11).
2. The thallus is spherical to oblong in shape but some species are pyriform or ovoid.
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3. The cell is somewhat pointed towards the anterior side and comparatively broader towards the posterior side.
4. The cell is surrounded by a cellulose cell wall which encloses the protoplasm.
5. The protoplasm consists of cytoplasm and a centrally located nucleus.
6. Anterior pointed end consists of an apical papilla.
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7. Two flagella are present on the anterior side of the cell. Both are of whiplash type.
8. At the base of each flagellum is present a basal granule orblepharoplast.
9. Both the flagella are equal in size and bigger than the size of the cell.
10. Below the basal granules are present two contractile vacuoles which are excretory in function.
11. Chloroplast is generally a cup-shaped structure in most of the species.
12. Each chloroplast encloses a single pyrenoid, which is the body of starch formation.
13. More than one pyrenoids are present in some species.
14. Many volutin granules are present in the cytoplasm.
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15. An orange coloured eyespot or stigma is situated in the protoplasm at the anterior end of the cell.
16. The eyespot is supposed to be photoreceptive in function.
Neuromotor Apparatus of Chlamydomonas:
1. It is also known as flagellar apparatus.
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2. It consists of following:
(i) Two blepharoplasts connected by a fibre called paradesmose (Fig. 12);
(ii) One of the blepharoplasts remains connected to the centrosome of the nucleus by a descending thread called rhizoplast;
(iii) Intranuclear or extranuclear centrosome is also connected with the nucleolus by a fibril.
Electron Micrograph of Chlamydomonas:
Study the microphotograph or its line diagram from the book:
1. This is the electron micrograph of Chlamydomonas (Fig. 13).
2. The cytoplasm is bounded by a cytoplasmic membrane.
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3. Cytoplasmic membrane consists of two electron opaque layers.
4. A few strands of granular endoplasmic reticulum, free ribosomes and mitochondria are visible near the periphery in the cytoplasm.
5. The chloroplast is cup-shaped. Inside the chloroplast lie the volutin granules, some strands of the granular reticulum tubulels, Golgi bodies, free ribosomes, etc.
6. Plate-like cristae are present in the mitochondria.
7. Single nucleus contains a large nucleolus.
8. Nuclear membrane is two-layered.
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9. Granular matrix of the cup-shaped chloroplast remains enclosed by a double membraned envelope.
10. In the granular matrix or stroma are present many tube like thylakoids.
11. Synthesized starch plates are present around the edge of the pyrenoid.
12. Pyrenoid lacks ribosomes.
13. Eyespot consists of 2-3 rows of globules which are arranged concentrically near the anterior end of the cell inside the chloroplast.
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14. Two contractile vacuoles are present.
15. Two long, whiplash type of flagella are present.
Palmella-Stage of Chlamydomonas:
1. It is a temporary phase in the life cycle resembling to the alga Palmella (Fig. 14).
2. Under unfavourable conditions, the cells become non-motile by loosing their flagella.
3. Divided parts of the protoplast of each cell remain surrounded by the mucilaginous matrix formed by the gelatinization of the cell walls.
4. Many such cells come together in the form of a colony surrounded by a common mucilaginous sheath and the whole structure resembles to the alga Palmella.
