- Algae are the simplest multicellular plants. Some are unicellular eg. Chlamydomonas
- Pant body: known as Thallus and they are avascular
- Habitat: Algae are usually aquatic, either freshwater or marine and some are terresterial.
- Algae are eukaryotic thallophytes.
- Algae are photoautotrophs.
- Storage form of food: Starch
- Reproduction: Algae reproduce either by vegetative, asexual or sexual method
- Vevetative method: fragmentation, hormogonia
- Asexual spore: zoospores, aplanospores, hypnospores, akinetes, azygospore
- Sexual method: isogamous, anisogamous, and oogamous gametic fusion
CLASSIFICATION OF ALGAE
On the basis of photosynthetic pigments algae classified into three classes.
- Chlorophyceae (green algae)
- Phaeophyceae (brown algae)
- Rhodophyceae (red algae).
1. Chlorophyceae (Green algae)
- It is the largest class of algae
- They are commonly known as green Algae.
- Photosynthetic pigments: They possesses chlorophyll a, chlorophyll b and small amount of β-carotenoids.
- The chloroplasts shows various shape ie. Spiral shape in Spirogyra, cup shaped in Chlamydomonas, star shaped in Zygnema, girdle shaped in Ulothrix
- Habitat: Mostly freshwater (Spirogyra, Oedogonium, Chlamydomonas, Volvox, etc), some are marine (Sargassum, Laminaria, etc) and some are parasitic (Polysiphonia, Harvevella, Cephaleuros)
- Distribution: they are cosmopolitan in distribution
- They are unicellular as well as multicellular.
- Each cell is eukaryotic
- Thalllus: their body structure, shape and size varies.
Chlamydomonas: unicellular free living
Volvox: colonial form
Spirogyra: multicellular, unbranched filamentous form
Ulva: multicellular, parenchymatous form
- Storage form of food: Starch
- Pyrenoids stores starch
- Cell wall has two layer: outer layer composed of pectose and inner layer is composed of cellulose
- Reproduction: vegetative, asexual and sexual method
- Vegetative : fragmentation
- Asexual: asexual sopre (akinete, aplanospore, azygospore)
- Sexual: isogamous, anisogamous, oogamous type gametic fusion
2. Phaeophyceae (Brown algae)
- Pheophyceae are called commonly known as brown algae
- Photosynthetic pigments: They possesses brown colored photosynthetic pigments fucoxanthin and β-carotenoids in addition to chlorophyll a and c.
- Habitat: They are almost marine, very few are fresh water eg.
- Thallus: they are multicellular brown algae. No unicellular and colonial (motile or non-motile) brown algae till known.
- Storage form of food: laminarin starch, manitol (alcohol) and some store iodine also.
- Reproduction: vegetative, asexual and sexual methods
- Vegetative: fragmentation.
- Asexual: asexual spores (motile zoospores).
- Sexual: isogamous or oogamous type gametic fusion.
3. Rhodophyceae (Red algae)
- Rhodophyceae are commonly known as Red Algae
- Photosynthetic pigments: They possesses Red colored photosynthetic pigments r-phycocyanin and r-phycoerythrin along with chlorophyll a, d, xanthophyll and β-carotenoid
- Habitat: They are aquatic, mostly marine. Some are freshwater e.g. Batrachospermum.
- Thallus: Red algae show a variety of life forms-
- Storage form of food: Floridean starch and floridosides sugar.
- Reproduction: vegetative, asexual and sexual mode
- Vegetative: fragmentation
- Asexual reproduction: non- motile spores( akinete, aplanospore, azygospore)
- sexual reproduction: Oogamous.
- Some species shows Alternation of generations in their life cycle.