Algae : Characteristics and Classification MCQ - Practice Questions with Answers

• Algae are chlorophyll - bearing, thalloid, avascular plants and are usually aquatic.

• Eg. Chlamydomonas, Volvox.

• Some of them form lichens along with fungi, some are epizoic on shells and sloth bear (algae Trichophilus welckeri). Some are present on moist stones, wood and soil.

•  Algae can be:

• unicellular flagellates like Chlamydomonas,  

• unicellular non-flagellates like Chlorella, colonial flagellates like Volvox, 

• coenobial non- flagellates like Scenedesmus, 

• unbranched filamentous forms like Spirogyra and  Ulothrix, 

• branched filamentous like Cladophora, heterotrichous like Fritschiella, 

• forms with nodal and intermodal demarcation like Chara

• massive body as in case of Kelps like Macrocystis (largest algae) and Laminaria.

• Reserve food is mainly starch. 

• Their cell wall is made up of cellulose, galactans and mannans

• Vascular tissue is absent.

• Vegetative reproduction occurs by fragmentation.

• Asexual reproduction occurs with the help of motile zoospores containing flagella.

• Sexual reproduction takes place by syngamy i.e. fusion of gametes. 

• Syngamy can be isogamy when fusing gametes are similar, anisogamy when fusing gametes are dissimilar or oogamy when female gamete is larger and non-motile while male gamete is smaller and motile. 

• Embryo formation is absent. 

• They increase the O₂ level in their environment. 

• The Life cycle of an alga can be 

1. Haplontic → Eg. Ulothrix, Spirogyra

2. Diplontic → Eg. Caulerpa

3. Diplohaplontic → Eg. Ulva, Cladophora.

On the basis of pigment distribution, storage food and cell wall composition, these  are classified mainly into three main classes 

1. Chlorophyceae (green algae).

2. Phaeophyceae (brown algae)

3. Rhodophyceae (Red algae).