UNIT TWO : ORIGIN AND EVOLUTION OF LIFE
Class : 11
Physiological and biochemical evidences
(i) Similarity in chemical composition
In all the living forms four major elements like C, H, O, N form organic compounds. In all the living organisms C, H, O combine to form carbohydrates and fats and with N to form proteins. The protoplasm in all living organism have the same composition. The basic unit of life is cell. Therefore, from above it can be concluded that living organisms might have evolved from a common ancestor.
(ii) Precipitation test (Serological Test)
The precipitations tests are used to determine and confirm the natural relationship due to the similarity of blood proteins. The degree of similarity between plasma proteins of various animals can be tested by the antigen-antibody technique. When the blood of man is mixed with the blood of monkey cat and dog, it gives high precipitation and when it is mixed with blood of orangutan, it gives less precipitation. When the blood of dog and cat is mixed together, it gives less precipitation. It proves that the cat and dog are closely related than the man and the man is closely related with the orangutan than cat and dog.
(iii) Enzymes and hormones
In large group of animals, there are similar types of enzymes and hormones are available. For example, the hormone like insulin and Thyroxin are similar and produced by all the vertebrates. The enzymes like lipase, amylase, trypsin are similar and produced by all the vertebrates. It suggests that they have common ancestry.
(iv) Genetic Evidences
Genetic deals with the heredity and variation of animals and plants. The DNA and RNA are called nucleic acids having genetic units found from virus to mammals with similar composition. The DNA has a double helical structure and is composed of similar type of nucleotides arranged in a linear fashion. Similarly, RNA is single stranded. The principles of genetic and its application are also quite similar in all organisms. The small segment of DNA represents gene in all the living life. This evidence also proves that the similarity among all the living organisms.
Tags:
Biology