Algae are chlorophyll bearing thallophytes, having simple, thalloid structure.
They have relatively undifferentiated tissues that never form true roots, stems or leaves.
They have a green pigment called chlorophyll.
In many algae, the green color is hidden by other pigments. Thus they may appear blue-green, brown, red or purple.
They are autotrophic plants. They manufacture their own food with the help of chlorohyll.
Algae are primarily aquatic, also grow on damp soil, rocks and wood.
Plant body of the alga is known as thallus.
Thallus of multicellular algae ranges from simple colony of cells, to filaments, to sheets of cells.
Cell wall is made up of cellulose.
They vary in size and form. They may be unicellular(Chlamydomonas), colonial(Volvox), filamentous(Ulothrix) or giant kelp(Laminaria).
Algae reproduce by vegetative, asexual and sexual method.
Vegetative reproduction is by fragmentation. Each fragment develops into thallus.
Asexual reproduction is by production of motile spores called zoospores.These spores on germination give rise to new thallus.
Sexual reproduction is by fusion of two gametes.
When the gametes are similar in size, they are called isogametes and their fusion is called isogamy.
When the gametes are dissimilar in size, their fusion is called anisogamy. The larger and non-motile is called female gamete and the smaller and motile is called male gamete sperm. Their fusion is called oogamy.
Economic Importance
(i) Algae are the main producers in marine ecosystem.
(ii) Being primary producers, they form the basis of food chains of all the aquatic animals.
(iii) At least half of the total carbon dioxide fixation on earth is carried out by algae.
(iv) Many species like Porphyra, Laminaria and Sargassum are used as food.
(v) Algin and Carrageenins produced by algae are used commercially.
(vi) Agar, used in bacterial culture and preparation of ice creams and jellies is obtained from Gelidium and Gracilaria.
(vii) Unicellular algae like Chlorella and Spirulina are rich in protein and are used as food supplements.
Classification of Algae
Chlorophyceae
The members of chlorophyceae are commonly called as Green algae.
They are aquatic, epiphytic, parasitic and epizoic.
The plant body may be unicellular, colonial or filamentous.
They have rigid cell wall with, an inner layer of cellulose and outer layer of pectose.
The have characteristic green colour due to presence of chlorophyll a and b.
The chloroplast may be, plate like, discoidal, cup shaped, spiral or ribbon shaped.
Most of the members have storage bodies called pyrenoids, located in chloroplasts.
Pyrenoids contain proteins and starch.
Some algae store food in the form of oil droplets.
They reproduce vegetatively (by fragmentation), asexually (Flagellated zoospores) and sexually (Isogamy, anisogamy, Oogamy).
Ex: Chlamydomonas, Ulothrix, Spirogyra, Volvox, Chara etc.
Phaeophyceae
They are commonly called as Brown algae.
They are marine forms, generally found in cool seas.
Plant body is filamentous and profusely branched forming kelps.
The cell wall is made up of cellulose which is covered by gelatinous algin.
The brown algae contains pigments chlorophyll-a,c , xanthophylls and carotenoids.
The golden brown or olive colour is due to the presence of fucoxanthin.
They anchor to substratum by holdfast and has large, flat, leaf like photosynthetic organs are called fronds. The ends are connected by stalk called stipe.
The food is stored in the form of laminarin starch or mannitol. Some stores as fat.
Vegetative reproduction is by fragmentation.
Asexual reproduction is by biflagellated zoospores. They have two unequal laterally attached flagella.
Sexual reproduction may be isogamous, anisogamous or oogamous. The male gametes are flagellated and female gametes are non-flagellated.
Some algae possess air bladders for buoyancy.
Ex: Laminaria, Sargassum, Dictyota, Fucus.
Rhodophyceae
They are commonly called as Red algae.
Most of the red algae are marine and found in warmer areas.
The cell wall is cellulose. It has polysaccharides called phycocolloids.
They are multicellular and have complex body organisation.
They have chlorophyll-a and a pigment r-phycoerythrin which gives red colour. Some species even have blue pigment, called anthocyanin.
Food stored in the form of floridean starch, which is similar to amylopectin and glycogen.
They reproduce by fragmentation. Sexual reproduction by oogamous type.
Ex: Porphyra, Gracilaria, Gelidium, Polysiphonia.
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They have relatively undifferentiated tissues that never form true roots, stems or leaves.
They have a green pigment called chlorophyll.
In many algae, the green color is hidden by other pigments. Thus they may appear blue-green, brown, red or purple.
They are autotrophic plants. They manufacture their own food with the help of chlorohyll.
Algae are primarily aquatic, also grow on damp soil, rocks and wood.
Plant body of the alga is known as thallus.
Thallus of multicellular algae ranges from simple colony of cells, to filaments, to sheets of cells.
Cell wall is made up of cellulose.
They vary in size and form. They may be unicellular(Chlamydomonas), colonial(Volvox), filamentous(Ulothrix) or giant kelp(Laminaria).
Algae reproduce by vegetative, asexual and sexual method.
Vegetative reproduction is by fragmentation. Each fragment develops into thallus.
Asexual reproduction is by production of motile spores called zoospores.These spores on germination give rise to new thallus.
Sexual reproduction is by fusion of two gametes.
When the gametes are similar in size, they are called isogametes and their fusion is called isogamy.
When the gametes are dissimilar in size, their fusion is called anisogamy. The larger and non-motile is called female gamete and the smaller and motile is called male gamete sperm. Their fusion is called oogamy.
Economic Importance
(i) Algae are the main producers in marine ecosystem.
(ii) Being primary producers, they form the basis of food chains of all the aquatic animals.
(iii) At least half of the total carbon dioxide fixation on earth is carried out by algae.
(iv) Many species like Porphyra, Laminaria and Sargassum are used as food.
(v) Algin and Carrageenins produced by algae are used commercially.
(vi) Agar, used in bacterial culture and preparation of ice creams and jellies is obtained from Gelidium and Gracilaria.
(vii) Unicellular algae like Chlorella and Spirulina are rich in protein and are used as food supplements.
Classification of Algae
Chlorophyceae
The members of chlorophyceae are commonly called as Green algae.
They are aquatic, epiphytic, parasitic and epizoic.
The plant body may be unicellular, colonial or filamentous.
They have rigid cell wall with, an inner layer of cellulose and outer layer of pectose.
The have characteristic green colour due to presence of chlorophyll a and b.
The chloroplast may be, plate like, discoidal, cup shaped, spiral or ribbon shaped.
Most of the members have storage bodies called pyrenoids, located in chloroplasts.
Pyrenoids contain proteins and starch.
Some algae store food in the form of oil droplets.
They reproduce vegetatively (by fragmentation), asexually (Flagellated zoospores) and sexually (Isogamy, anisogamy, Oogamy).
Ex: Chlamydomonas, Ulothrix, Spirogyra, Volvox, Chara etc.
Phaeophyceae
They are commonly called as Brown algae.
They are marine forms, generally found in cool seas.
Plant body is filamentous and profusely branched forming kelps.
The cell wall is made up of cellulose which is covered by gelatinous algin.
The brown algae contains pigments chlorophyll-a,c , xanthophylls and carotenoids.
The golden brown or olive colour is due to the presence of fucoxanthin.
They anchor to substratum by holdfast and has large, flat, leaf like photosynthetic organs are called fronds. The ends are connected by stalk called stipe.
The food is stored in the form of laminarin starch or mannitol. Some stores as fat.
Vegetative reproduction is by fragmentation.
Asexual reproduction is by biflagellated zoospores. They have two unequal laterally attached flagella.
Sexual reproduction may be isogamous, anisogamous or oogamous. The male gametes are flagellated and female gametes are non-flagellated.
Some algae possess air bladders for buoyancy.
Ex: Laminaria, Sargassum, Dictyota, Fucus.
Rhodophyceae
They are commonly called as Red algae.
Most of the red algae are marine and found in warmer areas.
The cell wall is cellulose. It has polysaccharides called phycocolloids.
They are multicellular and have complex body organisation.
They have chlorophyll-a and a pigment r-phycoerythrin which gives red colour. Some species even have blue pigment, called anthocyanin.
Food stored in the form of floridean starch, which is similar to amylopectin and glycogen.
They reproduce by fragmentation. Sexual reproduction by oogamous type.
Ex: Porphyra, Gracilaria, Gelidium, Polysiphonia.
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