What is Algae? Give various kinds of Reproduction in Algae

Algae are small microscopic plants and are mostly aquatic. Chlorophyll and other pigments are present in the body. Algae can manufacture food by normal process of photosynthesis and are called autotrophic. Cell wall is made up of cellulose. Starch is reserve food material. They grow in habitat where light is present. Usually asexual reproduction takes place and rarely sexual, also vegetative. Vegetative Reproduction: In this process portions of plant body are separated to give rise to new individuals without any change in the protoplast. Under favourable conditions it takes place by fragmentation in which whole plant body breaks up into small units which grow independently. In mynophyceae it takes place by hormogones formation. E.g. Plenrococcus. Asexual Reproduction: It takes place by:
 (1) By Zoospores: Zoospores are formed division of contents of parent cell. In filamentous forms like ulothrix zoospores are formed from older cells of the filament. Cytoplasm is divided to form zoospores which come out from mother cell wall. Zoospores are formed in favourable condition. Zoospores are motile and may be biflagellate or tetra flagellate or multi flagellate e.g. Vaucheria.
 (2) Palmella Stage: Sometimes zoospores do not come out of mother cell but remain surrounded by mucilaginous thread inside the mother cell. On division they form colony shaped structure of Pumella. On liberation they form new plants e.g. Chlanydomonas.
 (3) By Aplanospores: Aplanospores develop in unfavourable conditions. When motile phase of zoospores in eliminated the bodies are called Aplanospores. Each spore is surrounded by a wall. E.g. Ulothrix.
 (4) By Hipnospores: When alpanospores become thick walled and undergo a long resting period they are called hypnospores e.g. Sphaerella.
(5) A Kinetes: The protoplasm of single cell converts in a single akinete. Sometimes they are formed in chains. Each akinete may develop into a new plant e.g. ordogonuim, ulothrix. 
(6) Auto spores: Plants like Scenedesmus and some other chlrococales the resting spores develop all the structures of the parent cell in which they are formed and are similar to it except in size. These spores are called auto spores.
 (7) Cysts: In unfavourable condition the plant body of some algae like vaucheria become separate by transverse septa. Each segment forms many layered thick walled spore called cyst. During favourable conditions the cyst develops into new plant.
 (8) Endospores: The endospores are formed within the cells in blue green algae and Bacillariophyceae. Sexual Reproduction: It takes place by sex cells called gametes produced in cells called gametangia. Fusion may be as under:
 (1) In algae like chlanydononas, cladophore and ulothrix gametes may be identical i.e. gametes are similar and these gametes are called isogametes and sexual process is called isogamous reproduction.
 (2) In some algae like chlanydomonas brauni fusing gametes are different in size i.e. smaller active gametes and larger passive gametes. This sexual union is called anigogamous reproduction. In both above cases product of sexual union is called zygospore.
 (3) In some cases like ordogonuim and volvox young gametes are different in size. One of the gamete is small and motile while other is large and non motile. Former is called male gamete and other is female gamete or egg or oospore. This type of sexual reproduction is called ooganous and the product is called zygote or oospore. Zygospore or zygote develops into new plant on germination they may behave us under:
(i) Outer wall bursts and the contents surrounded by innes layer grow into new plant e.g. spirogyra.
(ii) Contents within the wall divide by meiosis to form a number of motile or non motile meisospores each of which on liberation develop into new plant e.g. Ulothrix.
(iii) Zygote divides mitotically to give rise to a small or a large diploid plant which produces the meisospores e.g. cladophora.