Algae

ALGAE

• Algae are chlorophyll containing thallophytes and are characterised by the absence of embryo stage and presence of unicelled non-jacketed gametangia. The study of algae is called algology or phycology.
• The main characteristics of algae are:

1.    Algae are usually aquatic, either marine or fresh water, or may occur in a variety of habitats like moist stones, soil and wood. 
2.    Reserve food is mainly starch. 
3.    Vascular tissues are absent. Being aquatic, water conduction is not required even in giant forms. 
4.    Nutrition is autotrophic. 
5.    Vegetative reproduction by means of fragmentation. 
6.    Asexual modes of reproduction by means of Mitospores like -Zoospores, Aplanospores, Hypnospores, Akinetes, Palmella stage, etc. 
7.    Sex organs are non-jacketed. They are unicellular. In case the sex organs are multicellular (e.g., Chara), every cell is fertile. 
8.    Sexual reproduction involves gametic fusion, that may be isogamy, anisogamy and oogamy in different groups. 
9.    Life cycle is of various types such as haplontic, diplontic or diplohaplontic. 

Concept Builder

1.    Algae shows a wide range of forms like -unicellular (e.g., Chlamydomonas), colonial (e.g., Volvox), palmelloid (e.g., Tetraspora), dendroid (e.g., Prasinocladus), filamentous unbranched (e.g., Spirogyra) or branched (e.g, Cladophora), heterotrichous (e.g., Fritschiella, Coleochaete, Stigeoclonium), siphonaceous (e.g., Vaucheria), parenchymatous (e.g., Ulva). 

2.    F.E. Fritsch (1935) in his book Structure and Reproduction In Algae proposed a practical and sound classification of algae. He divided algae in 11 classes on the basis of pigmentation, reserve food, flagellation, thallus structure and mode of reproduction. 

3.    Kingdom Plantae of Whittaker (1969) includes mainly three types of algae -red algae, brown algae and green algae. 

Comparison of Some Characteristics of Algae