Algae - An illustration with General features, classification , Economic importance , Examples

 

Overview-

• The algae belong to the sub phylum Thallophyta of the kingdom Protista in modern classification of organisms.

• Algae are chlorophyll-bearing, simple, thalloid, autotrophic eukaryotic organisms. During photosynthesis, they produce oxygen with help of light energy from the sun and form carbohydrates.

Economic importance of Algae-

• Algae are chief producers in the marine ecosystem. They fix almost half of atmospheric carbon di oxide through the photosynthesis.

Know about Where does Photosynthesis occur

• Algae are good source of carbohydrates, fats, proteins, and vitamins A, B, C, and E as well as the minerals like iron, potassium, magnesium etc. Therefore they are used as source of food.

• Some algae like spirullina and Chlorella is used by space travellar as food. Porphyra, Laminaria, sargassum and 70 species of marine algae used as source of food.

• In fishes, Algae plays a very important role because it helps in the production process. Fish used plankton and zooplankton as food.

• It helps in maintaining the health of the marine ecosystem because algae are naturally absorbent of carbon dioxide and also provide oxygen to the water.

• Algae are rich in minerals and vitamins. So they are also used as Biofertilizer which helps in increasing soil quality .

Know about Microbes used as Biofertilizer

• Algae are very sensitive. If there is a slight change in the environment their pigments change or might get died.  Water pollution is checked with the help of Algae like Euglena and Chlorella.

• Some algae like Gelidium and Gracilaria produce Agar that are used in making ice cream, jellies etc.

• Some algae produces algin and carrageen , water holding substances.

General features of Algae- 

Occurrence -

• They are found in both freshwater and marine water.

• They are found in a variety of habitats like moist stones, soils and wood. 

Association -

• Some of them make symbiotic association with fungi in the form of lichen. 

• Algae are also reported to be found in association with the animals like sloth bears. 

Size -

• They are unicellular and microscopic like Chlamydomonas to colonial forms like Volvox and to the filamentous forms like Ulothrix and Spirogyra.

• Some of the marine alga  form the kelp. Kelp may be hundred meter long.

Reproduction -

• The algae reproduce by vegetative, asexual and sexual methods.

• Vegetative reproduction is by fragmentation. Each fragment develops into a thallus.

• Asexual reproduction is by the production of different types of spores, the most common being the zoo spores.

• Zoospores are flagellated and motile and on germination give rise to new plants.

• Sexual reproduction takes place through fusion of two gametes.

• In Spirogyra The gametes can be flagellated and similar in size  or non-flagellated or non-motile.  Such reproduction is called isogamous.

• Fusion of two gametes dissimilar in size, as in some species of Chlamydomonas and Eudorina is termed as anisogamous. 

• If Fusion takes place between one large and non-motile female gamete and smaller motile male gamete is termed oogamous like  Volvox, Fucus.

Multiple Choice Questions on Algae

Classification of algae – 

• Algae are classified in to main three groups – Chlorophyceae, Phaeophyceae and Rhodophyceae

Chlorophyceae

• They are green algae and the largest group in Algae. 

• They are found in salt, fresh or brackish water.

• They are usually  green due to the presence  of pigments chlorophyll a and b.  They also have little amount of β-carotenoids .The pigments are present in chloroplasts.

• In Algae, the shape of chloroplast may vary from species to species.
• The chloroplasts shows various shape ie. Spiral shape in Spirogyra, cup shaped in Chlamydomonas, star shaped in Zygnema, girdle shaped in Ulothrix .

• Most of the members have one or more storage bodies called pyrenoids located in the chloroplasts. Pyrenoids contain protein besides starch.

• Green algae usually have a rigid cell wall made of cellulose and pectose.

• They store their food in form of starch and some members also store in form of oil droplet.

• Vegetative reproduction usually takes place by fragmentation or by formation of different types of spores.

• Asexual reproduction is by flagellated zoospores produced in zoosporangia.

• The sexual reproduction shows considerable variation in the type and formation of sex cells and it may be isogamous, anisogamous or oogamous.

• The number of flagella in green algae is 2 to 8 which are equal and located apically. For Ex- Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara Oedogonium

Pheophyeae-

• Pheophyceaen Algae  are commonly known as brown algae  and found primarily in marine habitats but rarely found in fresh water.

• They show great variation in size. Their size varies  from simple branched, filamentous forms like Ectocarpus and are   profusely branched  to form the  kelps.

• They possess chlorophyll a, c, carotenoids and xanthophylls.

• They are also found  in various  colours from olive green to brown depending upon the amount of the xanthophyll pigment, fucoxanthin present in them.

• Food is stored in the form of  complex carbohydrates, like laminarin or mannitol.

• The vegetative cells have a cellulosic wall usually covered on the outside by a gelatinous coating of algin..

• The plant body is usually attached to the substratum by a holdfast. They also have  stalks and stipes.

• They bear a  leaf-like photosynthetic organ called the frond.

• Vegetative reproduction takes place by fragmentation.

• Asexual reproduction in most brown algae is by biflagellate zoospores .

• Sexual reproduction may be isogamous, anisogamous or oogamous.

• Union of gametes may take place in water or within the oogonium.

• The gametes are pyriform  or pear-shaped with  two laterally flagella. For Ex- Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus

👌👌Remember - In this group, there are no unicellular and colonial brown algae reported so far.

Rhodophyceae-

• The members of Rhodophyceae are comonly known as Red algae.

• They have red colored photosynthetic pigments like  r-phycocyanin and r-phycoerythrin along with chlorophyll a, d, xanthophyll and β-carotene.

• They are aquatic and  marine  but like Batrachospermum some  are freshwater algae are also reported.

• They store reserve food in the form of Floridean starch.

• They are unicellular like Porphyridium or multicellular like  Geotrichum. 

• They reproduce Vegetatively by fragmentation.

• Akinete, aplanospore, azygospore are non motile spore involved in asexual reproduction.

• The  sexual reproduction is only of the Oogamous type and involve the fusion of non motile gamete.

• The sexual reproduction is accompanied by complex post fertilization development. 

• Some species like Batrachospermum , Polysiphonia exhibit Alternation of generations in their life cycle. For Example -Porphyridium, Gelidium, Gracilaria Batrachospermum , Polysiphonia.