ALGAE
Algae are chlorophyllous thallophytes characterised by absence of embryo stage and presence of non-jacketed gametangia with
fertile cells.
- As per Linnaeus’ two kingdom classification, all members of algae were grouped into plant kingdom along with bacteria and fungi.
- As per Whittaker’s classification, the members of algae were grouped in three kingdoms i.e., Monera (blue-green algae),
Protista (dinoflagellates, diatoms, etc.) and Plantae (Rhodophytes, Phaeophytes and Chlorophytes).
General Characteristics
- Habitat : Algae are of universal occurrence and they are found in a variety of habitats, such as freshwater, sea water, on snow,
on rocks and on/or within the plant and animal bodies. Of these, aquatic forms are most common. - Forms : Algae may be unicellular, colonial, filamentous, siphonaceous or parenchymatous.
- The algal plant body is covered by mucilage which protects it from epiphytic growth and decaying effect of water.
- Vascular and mechanical tissues are absent, therefore the body is flexible and easily gets swayed without being torn.
- Nutrition is photosynthetic. Grana are absent in chloroplast. The chloroplast varies in appearance among different algal forms,
e.g., cup shaped, girdle shaped, reticulate or ribbon shaped, discoid, spiral and stellate. - Algae contain chlorophyll a, b, c, d, e, carotenes and xanthophylls. Additional pigments like phycobilins, fucoxanthin occur in
specific groups. - Pyrenoids are associated with chloroplast for storage of starch. The reserve food may be starch, laminarin, mannitol, oil, fats, etc.,
which differ among different algal members. - Vegetative and asexual modes of reproduction are present. Vegetative reproduction may take place by fragmentation
(e.g., Ulothrix, Oedogonium), fission (e.g.,Chlamydomonas), hormogonia (e.g., Oscillatoria), tubers (e.g., Chara), budding
(e.g., Protosiphon), etc. - Asexual reproduction takes place by flagellated zoospores (e.g., Ulothrix, Oedogonium); non-motile, thin walled aplanospore
(e.g., Microspora) and non-motile, thick walled hypnospores (e.g., Pediastrum, Chlamydomonas nivalis), thick walled akinetes
(e.g., Cladophora), palmella stage (e.g., Chlamydomonas). - Under favourable conditions, algae show sexual reproduction which may be isogamous or heterogamous (i.e., anisogamous and
oogamous). Sex organs are non-jacketed and one celled called gametangia. - Life cycle may be haplontic, diplontic, haplobiontic and diplobiontic.
Glomerule
Main axis
Fig.: Batrachospermum
Lateral branch
(of unlimited
growth)
Erect system
Plurilocular
sporangium
Unilocular sporangium
Rhizoid
Fig.: Ectocarpus Fig.: Chlamydomonas
Flagellum
Flagellar canal
Mucilage
Vacuole
Contractile
vacuole
Volutin
granules
Plasma
membrane
Starch sheath
Pyrenoid
Cell wall
Nucleus
Chloroplast
Centrosome
Eye spot
Basal granule
Apical papilla
Prostate system