Q.Try to collect all the currently accepted meanings for the word 'species'. Discuss with your teacher the meaning of species in case of higher plants and animals on one hand, and bacteria on the other hand.

The word 'species' does not carry a single, fixed meaning for every group of organisms — its working definition shifts depending on the kind of life being classified.

• In taxonomy generally, a species is a group of individual organisms that share fundamental similarities and are set apart from closely related organisms by distinct morphological differences — differences of form and structure. For example, Mangifera indica, Solanum tuberosum and Panthera leo each name a distinct species by their specific epithet.
• For higher plants and animals, this shared-features-plus-morphological-distinction idea works well, because members of one species resemble one another closely and can be told apart from related species by their form and structure. …

When we try to pin down what 'species' means, the most useful starting point is the taxonomic one: a species is a group of individual organisms that share fundamental similarities with one another. What distinguishes one species from another closely related species are distinct morphological differences — differences in form and structure that let us tell them apart. In a scientific name it is the second word, the specific epithet, that identifies the species: in Mangifera indica (mango), Solanum tuberosum (potato) and Panthera leo (lion), the words indica, tuberosum and leo each name a species, while the first word names the genus above it.

A single genus may hold one or several species, all sharing morphological similarities yet each distinct. Panthera, for instance, contains leo (lion) and tigris (tiger); Solanum contains tuberosum, nigrum and melongena. In each case the species are recognised by the shared features that unite them and the structural differences that keep them apart.

• Higher plants and animals — here the morphology-based idea works well. Individuals of one species look fundamentally alike, and the differences in form and structure between one species and a related one are usually visible and reliable, so grouping and separating them by morphology is straightforward. …