Both organism and environment are affected by the interaction between them. Each DNA molecule is made of four chemical building blocks called nucleotides. The linear sequence of these four chemical letters encode the precise information in a gene, the unit of inheritance from parent to offspring. An organism's complex structural organization is specified by an enormous amount of coded information. Passing the information encoded in DNA from parent of offspring.
All forms of life use essentially the same genetic code.
A particular nucleotide sequence provides the same information to one organism as it does to another. Differences among organisms reflect differences in nucleotide sequence. Unity in Diversity Biological diversity is enormous. Estimates of total diversity range from 5 million to over 30 million species. To make this diversity more comprehensible, biologists classify species into categories.