1 Why do we classify organisms?
There are a wide range of life forms (about $10$ million -$13$ million species) around us. These life forms have existed and evolved on the Earth over millions of years ago. The huge range of these life forms makes it very difficult to study them one by one. Therefore, we look for similarities among them and classify them into different classes to study these different classes as a whole. Thus, classification makes our study easier.
2 Give three examples of the range of variations that you see in life-forms around you.
Examples of range of variations observed in daily life are:$\\$ (i) Variety of living organisms in terms of size ranges from microscopic bacteria to tall trees of $100$ metres.$\\$ (ii) The colour, shape, and size of snakes are completely different from those of lizards.$\\$ (iii) The life span of different organisms is also quite varied. For example, a crow lives for only $15$ years, whereas a parrot lives for about $140$ years.
3 Which do you think is a more basic characteristic for classifying organisms?$\\$ (a) The place where they live.$\\$ (b) The kind of cells they are made of. Why?
The kind of cells that living organisms are made up of is a more basic characteristic for classifying organisms, than on the basis of their habitat. This is because on the basis of the kind of cells, we can classify all living organisms into eukaryotes and prokaryotes. On the other hand, a habitat or the place where an organism lives is a very broad characteristic to be used as the basis for classifying organisms. For example, animals that live on land include earthworms, mosquitoes, butterfly, rats, elephants, tigers, etc. These animals do not resemble each other except for the fact that they share a common habitat. Therefore, the nature or kind of a cell is considered to be a fundamental characteristic for the classification of living organisms.
4 What is the primary characteristic on which the first division of organisms is made?
The primary characteristic on which the first division of organisms is made is the nature of the cell. It is considered to be the fundamental characteristic for classifying all living organisms. Nature of the cell includes the presence or absence of membrane-bound organelles. Therefore, on the basis of this fundamental characteristic, we can classify all living organisms into two broad categories of eukaryotes and prokaryotes. Then, further classification is made on the basis of cellularity or modes of nutrition.
5 On what basis are plants and animals put into different categories?
Plants and animals differ in many features such as the absence of chloroplasts, presence of cell wall, etc. But, locomotion is considered as the characteristic feature that separates animals from plants. This is because the absence of locomotion in plants gave rise to many structural changes such as the presence of a cell wall (for protection), the presence of chloroplasts (for photosynthesis) etc. Hence, locomotion is considered to be the basic characteristic as further differences arose because of this characteristic feature.