Algae-General characteristics and Classification

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

On the basis of photosynthetic pigments algae classified into three classes.

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.

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

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.

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-