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.

Newly discovered plant can be identified with the help of taxonomic keys, herbaria, monographs and preserved plant specimen. The scientist has to study the morphological and anatomical characters of the plants/plant parts, compare the characteristic features with the similar information available in the scientific literature and after that he can decide the exact systematic position of the plant, name it according to the rules of binomial nomenclature and fix it's systemic position.

Brassica campestris Linn

(a) Common name of the plant is mustard.

(b) The first part of the name denotes the generic name and the second part is the species name of the plant.

(c) According to ICBN, all scientific names are comprised of one generic name followed by a species name, which have to be written in italics always. It is a rule of bionomial nomenclature.

(d) Linn means Linnaeus was the first to discover the plant. He identified, named and classified the plant, so credit is given to him by adding suffix 'Linn', after the scientific name $B$. campestris Linn.