General characteristics of algae: 7 classes

Algae, diverse photosynthetic organisms found in various habitats, encompass seven major classes: Cyanophyceae (blue-green algae), Chlorophyceae (green algae), Xanthophyceae (yellow-green algae), Bacillariophyceae (diatoms), Phaeophyceae (brown algae), Rhodophyceae (red algae), and Chrysophyceae (golden algae). Each class exhibits unique pigments, cell structures, and life cycle characteristics, contributing to their ecological significance as primary producers and essential components of aquatic food webs.

1. Cyanophyceae (Blue-Green Algae):

• Habitat: Primarily freshwater, also found in marine and terrestrial environments.
• Pigments: Chlorophyll a, phycocyanin (blue), phycoerythrin (red).
• Storage Product: Cyanophycean starch.
• Cell Wall: Peptidoglycan, mucilage.
• Flagella: Absent.
• Reproduction: Primarily asexual (binary fission, fragmentation, hormogonia), rare sexual reproduction.
• Examples: Nostoc, Anabaena, Spirulina.

2. Chlorophyceae (Green Algae):

• Habitat: Freshwater, marine, and terrestrial.
• Pigments: Chlorophyll a, b.
• Storage Product: Starch.
• Cell Wall: Cellulose.
• Flagella: Present in some (zoospores, gametes).
• Reproduction: Asexual (zoospores, aplanospores) and sexual (isogamy, anisogamy, oogamy).
• Examples: Chlamydomonas, Spirogyra, Volvox.

3. Xanthophyceae (Yellow-Green Algae):

• Habitat: Primarily freshwater.
• Pigments: Chlorophyll a, c, carotenoids (yellow).
• Storage Product: Chrysolaminarin.
• Cell Wall: Cellulose, silica.
• Flagella: Present in some (zoospores, gametes).
• Reproduction: Asexual (zoospores, aplanospores) and sexual (isogamy, anisogamy, oogamy).
• Examples: Vaucheria.

4. Bacillariophyceae (Diatoms):

• Habitat: Freshwater and marine.
• Pigments: Chlorophyll a, c, fucoxanthin (brown).
• Storage Product: Chrysolaminarin.
• Cell Wall: Silica frustule (two halves).
• Flagella: Absent.
• Reproduction: Asexual (cell division) and sexual (oogamy).
• Examples: Navicula, Pinnularia.

5. Phaeophyceae (Brown Algae):

• Habitat: Mostly marine.
• Pigments: Chlorophyll a, c, fucoxanthin (brown).
• Storage Product: Laminarin, mannitol.
• Cell Wall: Cellulose, algin.
• Flagella: Present in some (zoospores, gametes).
• Reproduction: Asexual (fragmentation, zoospores) and sexual (isogamy, anisogamy, oogamy).
• Examples: Sargassum, Fucus, Laminaria (kelp).

6. Rhodophyceae (Red Algae):

• Habitat: Mostly marine.
• Pigments: Chlorophyll a, phycoerythrin (red), phycocyanin (blue).
• Storage Product: Floridean starch.
• Cell Wall: Cellulose, agar, carrageenan.
• Flagella: Absent.
• Reproduction: Asexual (monospores, tetraspores) and sexual (complex life cycle).
• Examples: Porphyra, Gracilaria, Gelidium.

7. Chrysophyceae (Golden Algae):

• Habitat: Primarily freshwater, some marine.
• Pigments: Chlorophyll a, c, fucoxanthin, carotenoids (golden-brown).
• Storage Product: Chrysolaminarin, oil.
• Cell Wall: Cellulose, sometimes with silica scales.
• Flagella: One or two flagella, sometimes absent.
• Reproduction: Asexual (cell division, statospores) and sexual (rare).
• Examples: Dinobryon, Synura.

A comparative Chart of all the characters for all 7 classes of Algae:

Characteristic	Cyanophyceae	Chlorophyceae	Xanthophyceae	Bacillariophyceae	Phaeophyceae	Rhodophyceae	Chrysophyceae
Habitat	Freshwater, marine, terrestrial	Freshwater, marine, terrestrial	Primarily freshwater	Freshwater, marine	Mostly marine	Mostly marine	Primarily freshwater, some marine
Pigments	Chlorophyll a, phycocyanin, phycoerythrin	Chlorophyll a, b	Chlorophyll a, c, carotenoids	Chlorophyll a, c, fucoxanthin	Chlorophyll a, c, fucoxanthin	Chlorophyll a, phycoerythrin, phycocyanin	Chlorophyll a, c, fucoxanthin, carotenoids
Storage Product	Cyanophycean starch	Starch	Chrysolaminarin	Chrysolaminarin	Laminarin, mannitol	Floridean starch	Chrysolaminarin, oil
Cell Wall	Peptidoglycan, mucilage	Cellulose	Cellulose, silica	Silica frustule	Cellulose, algin	Cellulose, agar, carrageenan	Cellulose, sometimes with silica scales
Flagella	Absent	Present in some	Present in some	Absent	Present in some	Absent	One or two flagella, sometimes absent
Reproduction	Asexual (binary fission, fragmentation, hormogonia), rare sexual	Asexual (zoospores, aplanospores) and sexual	Asexual (zoospores, aplanospores) and sexual	Asexual (cell division) and sexual (oogamy)	Asexual (fragmentation, zoospores) and sexual	Asexual (monospores, tetraspores) and sexual	Asexual (cell division, statospores) and sexual (rare)
Examples	Nostoc, Anabaena, Spirulina	Chlamydomonas, Spirogyra, Volvox	Vaucheria	Navicula, Pinnularia	Sargassum, Fucus, Laminaria	Porphyra, Gracilaria, Gelidium	Dinobryon, Synura