Tag: zoology

Organic evolution is the events involved in the evolutionary development of a species. It means that all life descended from other life, although features may have changed dramatically along the way. Organic evolution involves modifications to existing species, not the development of new ones. Darwin's finch is an example, which all evolved from a common species. Gradually these 13 species got modified and adapted to their particular niche and feeding habit within Galapagos island.

An ozone layer, present in the stratosphere, reflects the ultraviolet rays emitted by the sun and thus it prevents us from skin diseases and mutation.

The main factor responsible for the depletion of ozone layer is addition of Cl in the atmosphere.
Each Cl atom can destroy as many as 100,000 ozone molecules. Cl atoms comes from chlorofluorocarbons.

The depletion of the ozone layer was noticed in the year 1980.
The large scale destruction of the stratospheric ozone first came into focus in 1987 through the experiments in antarctica.

Maximum threat to the world is from ozone layer which is found in the stratosphere. This layer acts as a shield absorbing UV radiations from the sun. For the ozone layer to be intact there has to be a balance between the production and degradation which has been disturbed by the CFCs used in refrigerators. The F and Cl, which are released by these compounds results in the thinning out of the ozone layer also known as the ozone hole. It causes threat to life and environment as it leads to skin aging and cancers, snow blindness, cataract, melting of polar ice caps, global warming etc.

The UV radiations can cause mutation in the cells by altering the DNA. These are ionising radiations which can damage the structure of the DNA molecule. The UV rays can result in the formation of thymine dimers or split the hydrogen bonding. This results in distortion in the structure of DNA and the cell dies due to malfunctioning of the genetic material. 

When the destruction of the ozone layer increases, the amount of harmful ultraviolet radiation increases.
Note:
Ozone layer acts as natural sun block and shields us from the UV radiations of the sun which are dangerous to living organisms.
The ozone molecules absorb ultraviolet rays between 310 to 200 nm wavelength.
Ozone absorbs UV radiation to give back oxygen. Thus, the ozone layer acts as a screen and prevents the harmful radiations from reaching the surface of earth.

The hindbrain is the lowermost or rearmost region of the brain that bridges the brain with the spinal cord and includes the medulla oblongata, pons and cerebellum. It is also called the rhombencephalon.