Month: December 2015

Saccharomyces is commonly known as the yeast. S. cerevisiae is commonly known as the yeast. The cells are unicellular. The cells are rectangular, oval, and elliptical in outline. The cell wall is made up of chitin. Cellulose is absent. The vacuolated cytoplasm contains oil drops, volutin granules and various organelles like endoplasmic reticulum, ribosomes and dictyosomes. The central vacuole is surrounded by a limiting membrane called as tonoplast. Saccharomyces reproduces by vegetative means i.e. by fission and by budding. It also shows sexual reproduction during unfavorable conditions when the food supply is exhausting. Three types of life cycle are found i.e. Haplo-biontic life cycle , Diplobiontic life cycle, and Haplodiplobiontic life cycle.

Oscillatoria is found in rain water of pools, ponds, rivers, streams, lakes and in polluted water. Some of the species of Oscillatoria are plank tonic, some are found in hot water springs e.g O. terebriformis, and some species of Oscillatoria are found in saline waters. e.g. O. limosa. Oscillatoria in unbranched and filamentous. The trichome consists of cells which are arranged in uniseriate fashion. Oscillatoria species show Gaidukov phenomenon. Species of Oscillatoria can assume different shades when they are provided with light of different wavelengths. The trichome shows gliding movement as well as oscilllatory movement. During vegetative growth of the trichome, some cells of the trichome are filled with mucilage and become dead. These cells are called necridia. Thus Oscillatoria reproduces by the formation of Hormogonia and by fragmentation.

Cycas is an evergreen , palm like small tree. It grows in xerophytic habitats. The sporophytic plant body of Cycas is differentiated into roots, stem and leaves. The roots are of two types : Normal tap roots and coralloid roots. The leaves are also of two types i.e. dimorphic . The assimilatory leaves or foliage leaves and Scale leaves . The asexual reproduction takes place by the formation of sporangia and spores . The sporangia are arranged on the lower side of the microsporophyll in definite groups called sori. Sexual reproduction occurs by the formation of antheridia and archegonia.

Ectocarpus is a marine alga. The thallus is heterotrichous. It consists of a prostrate rhizoidal system and an erect branched system . The main pigment is xanthophyll. The cytoplasm contains polyphenol containing vacuoles called physodes. The asexual reproduction occurs by the formation of zoospores in two types of sporangia called unilocular sporangia and plurilocular sporangia. The sexual reproduction occurs by isogamy , morphological anisogamy and physiological anisogamy. In physiological anisogamy the male gametes are more active than the female gamete. Ectocarpus is a brown alga and shows Isomorphic alternation of generation.