The major groups of living things are the kingdoms. Previously, living things were categorized into two main groups; plantae and animalia kingdom. But this classification caused difficulties since some organisms seemed to posses some of the characteristics of both groups.
For example, euglena is capable of feeding like an animal and locomote like an animal. Therefore, it is placed in animalia kingdom. But the same euglena has chlorophyll and it is capable of manufacturing its own food.
Therefore, it should also be placed in plantae kingdom. Such an organism does not seem to fit exactly in animalia or plantae kingdom. Thus, euglenas are assigned in the major group of their own.
Currently, there are five major groups (kingdoms) of living things.
1.Kingdom monera
2.Kingdom protoctista
3.Kingdom fungi
4.Kingdom plantae
5.Kingdom animalia
Ranks of Classification
In the millions of organisms found on earth some are more similar while others are less similar. For example, all human beings resemble each other more closely than they resemble with the chimpanzees.Humans have more resemblance with chimpanzee than cats and dogs, and more like dogs than birds.Therefore when classifying the organisms, groups are established which are called ranks or taxa.
There are seven ranks of classification
1.Kingdom
2.Phylum/division
3.Class
4.Order
5.Family
6.Genus
7.Species
The highest rank of classification is the kingdom.
The lowest rank of classification is the species.
Every known organism has particular place in each group.
1. Kingdom- this is the highest rank (taxon). It comprises of several related taxa. It comprises of many organisms than any other taxon.
2. Phylum/division– this is the second largest rank of classification. It consists of several closely related classes.
3. Class - members or this group have more characteristics in common than do members of division or phylum.
4. Order- it consists of groups that are more alike than those in a class.
5. Family –this is made up of groups that are more alike than those in the order. Wolves and cats are both in the order Carnivore but wolves are in the family Canidae while cats belong to the family Felidae.
6. Genus – it consists of very similar species but members of different species cannot breed one another.
7. Species – Species can be defined as a group of closely related organisms which are capable of interbreeding and produce fertile offspring. It is the basic unit of scientific classification.
- Organisms that need to be placed in the same species must have the following characteristics:
b.Must be able to breed one another to produce fertile offspring.
c.Must be distinct and different from other organisms.
N.B: The term division is used by botanists instead of phylum when classifying plants or organisms related to plants.
Classification of some members of animals
| Human | Leopard | Domestic cat |
Kingdom | Animalia | Animalia | Animalia |
Phylum | Chordata | Chordata | Chordata |
Class | Mammalia | Mammalia | Mammalia |
Order | Primates | Carnivore | Carnivore |
Family | Hominidae | Felidae | Felidae |
Genus | Homo | Panthera | Felis |
Species | sapiens | padus | catus |
Scientific naming of living organisms
The scientific process of naming organisms is called nomenclature. Biological nomenclature is based on the binomial system (double naming system) pioneered by the work of a Swedish naturalist Carl Linnaeus (1707-1778).Biologists assign scientific names to organisms so as to avoid confusion among themselves since scientists from different countries use different languages. The scientific names are uniform in all languages.
Latin language is used in assigning the scientific name because it is an official language and that this language is no longer subject to changes; it is considered to be a dead language hence names once given remain unchanged.
Rules of binomial nomenclature
1. Scientific names of organisms must be in Latin language and if the names are derived from other languages, they must be latinized.2. A scientific name of an organism has two parts, genus name and species name.
3. A genus name always starts with a capital letter and a species name follows with a small letter.
4. In typed scripts, a scientific name must be written in italics or underlined if handwritten.
5. A specific name is sometimes accompanied with the name of the author who first described and named the organism.
6. When an organism is known by several names, the valid name is the one which was established after the work of Linnaeus.
Example...
Human being:Homo sapiens
Homo is the generic name and sapiens is the specific name.
Other examples of organisms with their scientific names
| Common name | Scientific name |
|---|---|
| Earthworm | Lumbricus terrestris |
| Cockroach | Periplaneta americana |
Coffee | Coffea | arabica |
Maize | Zea | mays |
Bean | Phaseolus | vulgaris |
Domestic cat | Felis | catus |
Sisal | Agave | sisalana |
Ashok tree | Polyanthia | longifolia |
Housefly | Musca | domestica |
Neem tree | Azadirachta | indica |
Flamboyant (Christmas tree) | Delonix | regia |
Tropical almond (mkungu) | Terminalia | catapa |
Amoeba | Amoeba | proteus |
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