Chlorophyceae: Green Algae
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Direct answer
Chlorophyceae, the green algae, are mostly fresh-water algae whose chloroplasts contain chlorophyll a and b, giving them the grass-green colour of higher plants. They store food as starch, have cell walls of an inner layer of cellulose and an outer layer of pectose, and bear two or more flagella of equal length inserted apically when motile cells are formed. Chlamydomonas (unicellular), Volvox (colonial) and Ulothrix, Spirogyra and Chara (filamentous) are the standard examples.
What you must remember
- Pigments: chlorophyll a and chlorophyll b, housed in definite chloroplasts; the green matches that of land plants, pointing to a common ancestry.
- Reserve food: starch, stored inside plastids.
- Cell wall: two layers — cellulose on the inside and pectose on the outside; pectose often dissolves in water to make the alga feel slimy.
- Flagella: when flagellate stages occur, flagella are two or more, equal in length and apical in position.
- Body forms: unicellular (Chlamydomonas), colonial (Volvox) and filamentous (Ulothrix, Spirogyra, Chara).
- Reproduction: vegetative by fragmentation; asexual by flagellated zoospores; sexual varying from isogamy (Spirogyra) through anisogamy to oogamy (Volvox).
- Habitat: largely fresh water, with some marine and terrestrial forms.
Common confusion
The three algal classes are separated cleanly by pigment, storage product and flagella — examiners scramble these. Green algae store starch like land plants, brown algae store mannitol and laminarin, and red algae store floridean starch; green and brown algae produce flagellate spores or gametes, but red algae completely lack flagella. A second trap is flagellar insertion: chlorophyceae bear equal apical flagella, phaeophyceae bear unequal lateral ones. Write the three-division comparison as three columns and never fill one column from memory of another.
Exam-focused takeaway
NEET asks green algae through characteristic-identification stems — "starch-storing algae with cellulose and pectose walls are..." — and through example matching with Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara. Sexual-reproduction vocabulary (isogamous, anisogamous, oogamous) frequently appears in assertion-reason form, with Spirogyra as the isogamous example. Expect at least one comparative question each year across the three algal divisions, so rehearse the full pigment-storage-wall-flagella matrix.
Frequently asked questions
Which pigments characterise chlorophyceae?
Chlorophyll a and b, the same pair found in higher plants, which is why green algae appear grass-green.
What is the storage product of green algae?
Starch, deposited within the chloroplasts.
What is the cell wall composition of chlorophyceae?
An inner cellulose layer and an outer pectose layer, the pectose often gelatinising in water.
Give one unicellular, one colonial and one filamentous green alga.
Chlamydomonas is unicellular, Volvox is colonial and Spirogyra is filamentous.
What types of sexual reproduction occur in chlorophyceae?
Isogamous fusion of similar gametes (Spirogyra), anisogamous fusion of dissimilar gametes and oogamous fusion of a large egg with a small motile gamete (Volvox).