As this topic is important for competitive examinations like SSC CGL, UPSC, etc. in this article, we will look into algae and its types.

1. Algae are divided into three main classes: Chlorophyceae, Phaeophyceae and Rhodophyceae.

2. Algae are commonly found in fresh, brackish and salty waters.


3. Chlorophyceae:

a. These are commonly known as green algae.

b. The plant body may be unicellular, colonial or filamentous.

c. They are usually bright green in colour due to the dominance of pigments like chlorophyll a and chlorophyll b and are located in chloroplast (discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped organelle which differs with species).

d. Reproduction takes place by vegetative, asexual and sexual methods. Vegetative reproduction takes place by fragmentation or by formation of different types of spores while asexual reproduction takes place by flagellated zoospores. Sexual reproduction, however, shows variation in the type and formation of sex cells which can be isogamous, anisogamous or oogamous.

e. Green algae stores food in the form of starch.

f. Some commonly found green algae are: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara. Chlamydomonas and Volvox are important organisms for research purpose. The latter serves as a model organism for understanding cell death and cell interactions.

4. Phaeophyceae:

a. These are commonly known as brown algae.

b. Varying abundantly in size and form, they are simple branched, filamentous forms (for eg. Ectocarpus) to abundantly branched forms as represented by kelps that may grow as high as 100 metres.

c. Their colour ranges from olive green to different shades of brown due to the presence of chlorophyll a, c, carotenoids and xanthophylls.

d. Reproduction takes place by vegetative, asexual and sexual methods. Vegetative reproduction takes place by fragmentation while asexual reproduction (common in most brown algae) takes place by biflagellate. Sexual reproduction may be isogamous, anisogamous or oogamous.

e. The vegetative cells have a wall made up of cellulose covered on the outside by a gelatinous coating of algin. The protoplast contains plastids, a centrally-located vacuole and a nucleus. The plant body is usually attached to the substratum by a holdfast, and has a stalk, the stipe and leaf like photosynthetic organ – the frond.

f. Brown algae store food in the form of Mannitol and Laminarin.

g. Some commonly found brown algae are Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus.

Algin (also known as alginic acid or alginate) has a variety of applications. It is used as a thickener or stabiliser in many products like ice cream, jelly beans, latex paint, paper, textiles, toothpastes and floor polish.

h. It is also used in pharmaceutical preparations and as an impression making material in dentistry and prosthetics.

5. Rhodophyceae:

a. These are commonly known as red algae due the presence of phycoerythrin, the pigment which absorbs blue light and reflects red light.

b. The red thalli of most of the red algae are multicellular. Some of them have complex body organisation.

c. Red algae are predominantly marine and are found in warmer areas. They can be found in both well-lit regions near to the surface of water and also at great depths in oceans where light penetration is relatively less.

d. Reproduction takes place by vegetative, asexual and sexual methods. Vegetative reproduction takes place by fragmentation, while asexual reproduction by non-motile spores and sexual reproduction by non-motile gametes (oogamous).

e. Red algae stores food in the form of Floridean starch.

f. Some common members of red algae are Polysiphonia, Porphyra, Gracilaria and Gelidium.

g. Carrageenan, an extract obtained from red algae, is widely used in the food industry for their gelling, thickening, and stabilising properties. They are mainly used is in dairy and meat products due to their strong binding to proteins. It is also used pharmaceutical products laxatives, capsules and tablets, lotions and creams, shampoos, ulcer products and toothpastes. Industrially, it is used in air freshener gels, tertiary oil treatment, cleaners, enzyme immobilisation, electrophoretic media, chromatographic media.

h. Agar, which is another extract from red algae is used as a colloidal agent for thickening, suspending, and stabilising. It is also used in pharmaceutical products (laxatives, capsules and tablets, suppositories, radiology suspending agents, anticoagulants, etc.) and in industrial purposes for making adhesives, in textile printing, dyeing, castings and impressions.

6. Algal bloom:

a. It is a natural phenomenon when there is a rapid increase in the concentration of algae resulting in toxic or harmful effects on people, fishes, shellfishes, marine mammals, and birds. However, its frequency, duration and intensity increases with eutrophication (presence of excessive nutrients in the water).

b. Eutrophication results in nutrients finding their way into the water from the fertilizer used on farms, lawns as well as waste water and stormwater runoffs. When this runoff combines with abundant sunlight and warm temperatures, algae blooms may occur.

c. Algal blooms cover the surface of water with a thick scum which obstructs the penetration of sunlight, thereby affecting the rate of photosynthesis (process that produces oxygen). Thus, the amount of dissolved oxygen in the water gradually decreases resulting in suffocation of aquatic flora and fauna that solely depend on the dissolved oxygen available.

d. Red tide is a common term used for harmful algal blooms caused by some species of algae and dinoflagellates (unicellular protists that are mostly photosynthetic and found abundantly in marine waters).

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