There is a need to standardise the naming of living organisms such that a particular organism is known by the same name all over the world. Botanists have solved this problem by setting International Code for Botanical Nomenclature (ICBN). Scientific naming ensures that each organism has only one name in any part of the world. ICBN ensures that such name has not been used for any other organism.

Each name has two components the generic name and the specific epithet. This system of naming is called bionomial nomenclature given by Carolus Linnaeus. e.g., mango has the scientific name Mangifera indica and potato is known as Solanum tuberosum.

Solanum is the largest genus of flowering plants which includes few economically important plants, e.g., potato, tomato, tobacco and brinjal. All these plants show some common morphological structures related to vegetative and reproductive similarities. So, they have the same common name of genus Solanum.

Cell, the basic structural and functional unit is composed of many cell organelles, i.e., ER, Golgi apparatus, ribosomes, mitochondria, chloroplasts etc., each with a specific function. Each of these organcells are made up of various moleclules such as proteins, lipids, enzymes, metallic ions like $\mathrm{Mg}^{2+}, \mathrm{Ca}^{2+}, \mathrm{Mn}^{2+}, \mathrm{Na}^{+}$etc, which helps in the functioning of cell organelles.

e.g., molecular constituents like proteins (60-70\%), lipids (25-30\%), RNA (5-7\%) DNA, $\mathrm{Mn}^{2+}$ ETS, ATP synthase, etc. found in mitochondria function togather in a coordinated way to carry out cellular respiration and release energy, thus making it power house of cell.

Thus, the molecular constituents of a cell organelle, forms the basis of its functioning irrespective of its individual molecular properties.

The number and kind of organism is not constant, because of the following reasons Mechanisms adding new organisms by

(i) Sexual reproduction

(ii) Mutation

(iii) Evolution

Mechanisms reduing the number of organisms are

(i) Environmental threats

(ii) Loss of habitat

(iii) Anthropogenic activities

The living organism exhibit distinctive characteristics, which are as follows

(i) Growth All living organisms grow in size as well as in number. Plants show growth all through their life whereas animals up to a certain growth period after which growth ceases.

(ii) Reproduction The process of reproduction is essential for the continuity of life on earth. Every organism whether unicelluar or multicellular gives rise to an individual of its own kind. Lower organisms usually reproduce asexually, e.g., Hydra, fungi, yeast, etc.

Sexual reproduction is found in advanced group of organisms, which involves two parents. In Amoeba growth and reproduction however is synonymous.

(iii) Metabolism There are thousands of enzymatically controlled reactions occurring in all living cells. These are synthesising (anabolic) and breaking down (catabolic) reactions. Hence, it is the most important characteristic of living organisms.

(iv) Response to stimuli Consciousness and response to stimulus is the defining property of all living organisms. Plants respond to light, water temperature. Unicellular organisms also sense their environment and respond accordingly.

(v) Cellular organisation The cellular organisation of the body is the defining feature of life forms. Cells work together in hierarchial manner group of cells make tissues, tissues make organs, organs make systems, systems when work in co-ordination form an individual.

So, we can say living organisms are self replicating, evolving and capable of responding to external stimuli.