As per rough estimate, a total number of species present on planet earth are 8.7 million. These species are widely distributed, both on the terrestrial earth and inside the ocean. A rough distribution of these species is given in the Table 1.2.

TABLE 1.2 Distribution of organisms on earth

As given in the Table 1.2, the distribution of different species gives salient feature of biodiversity. These features are as follows:
1.  Shape: The shape of different species present varied a lot. Within the prokaryotes, bacteria of different shapes such as bacilli, cocci etc are found. In eukaryotes, plants are found with different shapes.

2. Size: The shape of different organisms varies from very tiny virus to giant blue whale.

3. Spatial distribution: Living organisms are distributed from extreme cold weather to very hot region of the planet. They are also distributed on land, water and in the air as well.

4. Biological Activity: Due to their wide distribution of species to the extreme condition, species have devised the metabolic activities to adopt to these conditions.

Outline of the course content: With such a brief introduction, you might have realized the complexicity and diversity of the different organisms found on the earth. Within the diversity, most of the organism follows similar basic steps to complete their life-cycle. In addition, interaction of these species give appearance of newer species or original species with extra features. The understanding basic features of living system and different steps involved to run their life-cycle as well as the known mechanism of appearance of newer species