Know about virus

The Russian Botanist D.I Ivanowsky prepared an infectious extracts from tobacco plants that were suffering from mosaic disease. When the extract was allowed to pass through a filter which is able to prevent the passage of bacteria, the filtered fluid was still infectious. In 1898 , Beijerink coined the name 'virus' (Latin-poison) due to infectious nature. Mayer (1886), Beijirink (1898) established the existence of viruses by discovering many viral diseases in plants and animals. In 1900, Walter Reed discovered the virus of yellow fever , the first known viral disease of man. In 1915, F.W Twort and F.D Herelle independently noticed that bacteria were also infected by virus and those viruses that infect only bacterias were named as bacteriophase. Schelsinger (1933) was first to determine the chemical composition of viruses.Wendell Stanley, in 1935 isolated a virus in a crystalline form and reported that viruses were made exclusively of proteins. Pirie and Bawden (1936 ) give the concept that viruses are made up of nucleic acid and protein. Likewise, Harshey and Chase (1952) showed that only he nucleic acid is responsible for infection but protein is non infectious.

In 1981, Matthews defined virus as the set of one or more nucleic acid molecules enclosed in a protective coat of protein and able to organize its own replication within a suitable host cell.
Viruses are the causative agents of many infectious diseases like mumps, common cold, flu, small pox etc. It is an obligatory parasitic pathogen with at least one dimension of less than 200 millimicrons; on average they are about 50 times smaller than bacteria. They do not have a cellular structure or any metabolic activity as they do not have enzyme systems and protein synthesis machinery and cannot reproduce outside living cells . They can be recognised only by their biological behaviour such as, by the disease they cause. Their exact nature was a mystery for long. Most of the virus have only one nucleic acid DNA or RNA. Rous sacroma virus, producing certain cancer is only virus having both DNA and RNA . Some small viruses have been crystallised and behave as chemical like TMV and poliomyelitis.

Viruses are found in
1. Helical shape eg. TMV, influenza virus.
2. Polyhedral shape eg. polio virus
3. Tadpole shape eg. bacteriophases

Viruses are broadly classified into following types.
1. Plant virus: Virus which infects only plant is known as plant virus. Their genetic material is RNA. The first plant virus to discover was Tobacco Mosaic Virus . eg of plant virus are bean mosaic virus, potato virus.
2. Animal virus: Virus which infects only animal is known as animal virus. Their genetic material is DNA. eg. rabies virus
3. Bacteriophase: Virus infecting bacterial cell is known as bacteriophase. They contain DNA as genetic material.

They are also classified based on the type of their nucleic acid which are as follows:
1. DNA virus (Deoxyvira): Virus containing DNA is known as DNA virus.
2. RNA virus (Ribovira): Virus containing RNA is known as RNA virus.

How clouds remain in the sky?

There exists an attraction between any two bodies in this universe which is known as force of gravitation. When a body is allowed to fall freely, the body will be attracted towards the earth due to the force of gravity. But we see clouds floating in the sky. Doesn't the earth's force of gravity affect the cloud?

Actually, it is not true to say that clouds always remain in the sky. Some type of clouds remain on the surface of earth such as fog. There are traces of water vapour in air. When air is cooled these traces of water vapour changes into small droplets of water. Cloud is the group of these droplets of water. Flowing air helps cloud to remain in the sky.

But due to air, cloud when goes higher than the surface of the earth it becomes more cold. Now the cloud which is becoming colder and colder the small water droplets come in contact and becomes a huge one. The flowing air can't withstand the cloud which is formed due to big droplets of water and due to force of gravity it falls on earth in the form of rain.

Relation of biology with other sciences

All the disciplines of science are related to each other. Biology is such a subject which can't be studied in isolation. So, the term biology is broadly named as 'life science' so as to cover its wide scope which involves the knowledge from other sciences such as physics, chemistry, geography etc. as a result other new branches of biology have been introduced
Biophysics,Biochemistry,Biogeography. These involves the knowledge of application of physics, chemistry, and geography respectively. in order to describe all the phenomenon of biology.
Some of the examples of interrelation of biology with other branches of science are:
1. With physics
a. Study on the structure functioning of human eye requires knowledge of optics.
b. Sunlight is necessary for photosynthesis.
c. Result of photosynthesis and respiration is the production of oxygen and carbondioxide .
d. Heat energy is required for maintenance of life.
e. Conduction of water in plants from root to the leaf is provided by the properties of adhesion and cohesion of water molecules and capillary system.
f. Study of photoperiods on flowering of plants involves stimulus of light.
g. Chemical energy is transferred to heat energy as a result of consumption of ATP.
h. Many biological instruments such as microscope, chromatography, x-ray diffraction, fractionation, autoradiography etc. follow the physical applications.
2. With chemistry
a. All living organisms are composed of organic and inorganic compounds.
b. Molecules are broken down or synthesized in metabolic processes.
c. Molecules move in and out of the cells by diffusion and osmosis.
d. Transportation of oxygen needs haemoglobin to form oxyhaemoglobin.
e. For proper functioning acid base equilibrium in a cell maintains the PH of the protoplasm.
3. With geography
a. Study of distribution of communities always involves the knowledge of geography.
b. Distribution , adaptation, and evolution are related with the climate of area.
4. With mathematics and statistics
a. Census of wild animals is based on application of mathematics and statistical applications.
5. With sociology
a. study of human behaviour, social relationship and antisocial relationship for example criminals terrorists etc. requires the study on human nervous system and study of glands, hormones etc. It also requires the knowledge of principles of inheritance, pedigree analysis etc.