Monthly archives: March, 2012

Viruses

Introduction Viruses are still biologists’ puzzle because they show both living and nonliving characters. Hence viruses are regarded as a separate entity. It is not taken into account in Whittaker’s five kingdom classification. Viruses are now defined as ultramicroscopic, disease causing intra cellular obligate parasites. Brief history of discovery Viruses were not known to biologists …

Growth of Microbes

Living organisms grow and reproduce. The growth indicates that an organism is in active metabolism. In plants and animals one see the increase in height or size. In a butterfly, a small larva hatching from egg grows in size, moults, pupates and become an adult butterfly through metamorphosis. Growth in a common use refers to …

Autotrophs and Heterotrophs

Based on the source of carbon microorganisms are grouped as autotrophs and heterotrophs. Some can use CO2 as their sole source of carbon like plants and algae are termed as autotrophs. Others like some bacteria, fungi and actinomycetes utilize preformed organic compounds as carbon source and hence called heterotrophs. Most organisms that involve in decomposition …

Systematics

Diversity in living organisms There is a great diversity among living organisms found on the planet earth. They differ in their structure, habit, habitat, mode of nutrition, and physiology. The Biodiversity of the earth is enormous. Current estimates suggest that the earth may have anywhere from 10 to over 40 million species of organisms, but …

Diversity of Chordates

The chordates exhibit an astonishing diversity in form, physiology and habits. The number of chordate species is limited. About 49,000 species are on record which are only half of the living species of molluscs and less than one tenth of arthropods. Despite their modest number of species, the chordates make remarkable contribution to the bio-mass …

Transpiration Pull Theory

This is also called as cohesion-tension theory put forward by Dixon and Joly (1894) and supported by Renner, Curtis and Clark. This theory is based on a number of features. Cohesion and Adhesion Mutual attraction between water molecules is called cohesion and this force may have a value as high as 350 atmospheres. The wall …

Water Transport in Plants

The water absorbed by the root hairs is translocated upwards through the xylem. The mystery of the upward movement of water is yet to be solved in a satisfactory way. The upward transport of water in plants which are 400 feet high has not been satisfactorily explained till date. Though the mechanism for upward movement …

Microbial growth and nutrition

‘An army marches on its stomach’ said Napolean Bonapart.This indicates that food is important for any living organism and so also for microbes. Food is any substrate that can be metabolized to provide assimilable material or energy for the cell. Plants synthesize their own food requirements through photosynthesis. Animals ingest the presynthesized food from plants …

Pure Culture Methods

In the natural environments microorganisms exist in mixed cultures. To establish the role of microbial agent to a disease process, it is essential to demonstrate the organisms or its components in the diseased tissues. To accomplish this, the organism must be cultivated from the tissues. Similarly to know the kinds of organism present in the …

Plasma Membrane

fluid-mosaic-model-of-the-cell-membrane

It is the outer limiting membrane of both prokaryotic and eukaryotic cells. It is an ultra thin, elastic, living membrane. Plasma membrane is a dynamic and selective transport barrier. Since the plasma membrane is ultra thin, it could be observed only under electron microscope. Structure of the membrane is studied by isolating the same from …