Unit 6: The diversity of life                                                         1   2   3

1. Classification of living beings

1.1. Groups of living beings

Taxonomy is the science that orders and classifies living creatures.

The classification of living beings allows us to organise them into groups, called taxa, based on the characteristics that define them.

Classification criteria are the features that allow scientists group together determined living things and distinguish them from others.

Every group (taxon) can be divided into other smaller groups following other criteria. We can continue the process making smaller and smaller groups that are contained whitin the previous one. This type of classification is known as hierarchic.

Each group or category is called taxonomic rank. The main taxonomic ranks

are: kingdom, phylum, class, order, family, genus and species.

Each kingdom includes several phyla, each phylum includes several classes,

each class includes several orders, each order includes several families,

each family includes several genera and each genus includes several species.

1.2. Species

The most important taxonomic rank is the species. A species is a set of living beings which are physically similar and which can reproduce among them and produce fertile descendants or offspring.

1.3. Naming living beings

Binomial nomenclature is a standard convention used for naming species.

This system of nomenclature was developed by Carl Von Linnaeus,

a Swedish naturalist in the 18th century.

The scientific name helps us to identify a species without doubts

because common names can vary from one place to another.

The scientific name of every species is the combination of two words:

the genus (generic name) and the species (called specific name).

The species name refers to a characteristic of the species (size, colour, etc) or to the name of its discoverer or to the place where it was discovered.

The scientific name can give us information about the evolutionary relationship between organisms: two species with the same generic name have a closer relationship than two species with different generic names.

Animation: Classifying organisms

1.1. What two organisms of every one of the following groups are more  

closely related? (Underline them) Why?

a. Populus alba – Pinus nigra – Populus nigra

b. Equus caballus – Equus zebra – Hyla cinerea

c. Lavandula officinalis – Valeriana officinalis – Lavandula angustifolia

1.2. Imagine that you have discovered these new organisms for science,

        how would you call them?

a. A very little bird of Turdus genus.

b. A plant with flowers with lots of colours, of Peonia genus.

c. A harmless spider of Lycosa genus

1.3. This sketch represents the species that are in the same class.

1.4. Listen to the following sentences and indicate if they are false or true.