Introduction :
Biology is a natural science concerned with the study of life and living organism i.e.,plants and animals.Study of plants is called Botany and study of animals is called Zoology and Botany are collectively called biology.The term 'Biology' was coined by Lamarck and Treviranus.The scientist,who gave his thought for the first time about the life of plants and animals was Aristotle.That's why he is known as the Father of Biology.He is also known as the father of Zoology.Theophrastus is known as Father of Botany.
Characteristics of Living Beings
Respirations,Reproductions,Excretion,movement and tendency to respond outer environment are the important characteristics of living things
THE CELL
The Cell is the basic structural and functional unit of all known living organisms.The branch of Biology ,which deals with the study of cell,is called Cytology.
Rpbert Hooke coined the term cell,when he saw honey comb-like structure in the section of cork.However ,he only discovered cell wall.The first living cell was discovered by Leeuwenhoek.A typical cell consist of protoplasm,i.e.,nucleus and cytoplasm.
Function of Cell
Cell wall provide shape and rigidity to the cell.Mitochondria is called the power house of a cell,because in it stepwise oxidation of fuel occurs,which results in release of chemical energy.This energy is stored in the form of ATP.
Plastids are present only in plant cells and are of three types - Chloroplasts,leucoplasts and chromoplasts.Chloroplast is the site of photosynthesis as it contains chlorophyll.Chloroplas is called the Kitchen of the cell.
Lysossomes are polymorphic organelles having hydrochloric enzymes .These enzymes function at acidic pH=5.These are sometimes called suicidal bags of the cell.
Nucleus was discovered by Robert Brown.It contains nucleoplasm,nucleolus and chromotin material.Chromatin is controlling centre of cell as it contains chromosomes.
Nucleic Acids
It contains the genetic instructions used in the development and functioning of all known living organisms.These are of two types DNA and RNA
Deoxiribo nucleic Acid(DNA)
It is a long polymer made from repeating units called nucleotides.Each nucleotide consist of a nucleoside and a phosphate group,joined together by ester bonds.It has four bases i.e.,adenine,guanine,cytosine and thymine.Adenine and guanine are the purine bases ; cytosine and thymine are pyramidine bases.
Ribo Nucleic Acid(RNA)
It is also made up of a long chain of nucleotides.Each nucleotides consists of a nitrogenous base, a ribose sugar and a phosphate group .Here thymine is replaced by Uracil(U)
Chromosome
Chromosome is thred-like structure,found in the nucleus.Bead like structure found on chromosome is called genes,which are made up of DNA.Number of pairs of chromosomes :
Human....23 (=46)
Dog....39 (=78)
Monkey....21 (=42)
Onion....8 (=16)