THE FIVE KINGDOMS AND THE HIERARCHY OF CLASSIFICATION

Learning Objectives
   After reading this, you  should be able to:
- Outline the general characteristics of the five kingdoms of living organisms.

- Identify and classify organisms Into their respective kingdoms.




Biological classification is the sorting out of living things into groups according to their common characteristics.

Each group is then split into smaller groups, and these groups into even smaller groups and so on. The members of each group have certain things in common which distinguishes them from other groups.


Living things are first split into kingdoms SUCh as the animal and plant kingdoms. The kingdoms are then split up into a large number of smaller groups called phyla (singular: phylum). All the members of phylum is broken down into classes, classes into order; orders into families, families into genera (singular: genus) and genera into species. Each of these groups contain progressively fewer and fewer kinds of organisms. Thus, a phylum contains a wide variety of organisms.

They all have certain basic features in common, but there are a lot of differences amongst them.

The organisms belonging to a genus are all similar with few differences between them compared to those in the phylum. Those belonging to the same species are identical in general appearance. They are the only Organisms that can interbreed among themselves to produce fertile offsprings.

It is interesting to note that, similarities among organisms increases from kingdom to species and hence, differences among the organisms increases from species to kingdom. For instance the kingdom, Animalia has several animals including man; spider; lizard; earthworm; cockroach; elephant; frog; etc. One can easily note the gross differences among these organisms but in the species, Homo sapiens there is only man and woman. Any organism can therefore be classified into seven ranks in an orderly graded manner from kingdom; phylum; Class; order; family; genus and species. In this classification, kingdom is the largest rank and species is the last and the smallest rank.


IMPORTANCE OF CLASSIFICATION
     There are about one-and-a-half million different kinds of living organisms that have been discovered on the earth, and it has also been estimated that, there may be ten to hundred million different kinds of organisms. The question one may ask is how biologists study all these kinds of organisms. Definitely, it would be extremer difficult if not impossible. However, the answer is found in classification. Classification sorts and puts every organism into a systematic order for easy identification and study. It allows adequate information about a particular organism to be found more readily.

Classification enables us to indicate
relationship between different categories of organisms. This is because, it is primarily based on the common features of the organism.
It gives us an idea as to the way in which they have evolved, looking at similar structures from studies of comparative anatomy, paleontology (study of fossils), embryology, etc. Because classification is based primarily on the common features of organisms, it helps to give a universal scientific name to every species which is internationally accepted, so that students of different languages know the scientific name.


GENERAL CHARACTERISTICS OF KINGDOMS
With the exception of viruses, all living organisms are classified into five kingdoms.
Each kingdom has its own features or characteristics. The kingdoms are: prokaryotae; protoctista; Fungi; Plantae; and Animalia.





KINGDOM : PROKARYOTAE / MONERA
The kingdom consists of micro organisms which are unicellular. They are mainly bacteria and blue-green algas. They are found in the soil, water, air and on animals and plants bodies. Most bacteria are mobile due to the Presence of one or more flagella.


GENERAL CHARACTERISTIC OF THE KINGDOM PROKARYOTAE / MONERA They are unicellular organisms. They have no nuclear membrane surrounding the nucleus therefore, it is not regarded as nucleus, instead it is known as nuclear materials. They exhibit asexual reproduction. Their genetic materials are scattered in the cytoplasm. Some have flagella, which enable them move from one place to the other. They lack organelles like mitochondrion, endoplasmic reticulum, etc. Forms of bacteria; Cocci (spherical cells), Bacilli (cylindrically-shaped cells) vibrio (comma shaped cells) and spirilla (spiral cells).





KINGDOM: PROTOCTISTA .
This kingdom is made up of eukaryotic organisms. They are neither plants; animals nor fungi.

GENERAL CHARACTERISTICS
They are mostly unicellular organisms. They have distinct nucleus which is enclosed in a nuclear membrane. Their organelles are surrounded by a membrane. However, they lack tissues and organs.

The kingdom is classified into eight phyla.
These include plant-like forms (algae) which possess chlorophyll, also animal like protozoa and forms which have both plant and animal-like features (euglena flagellates).





KINGDOM : FUNGI
      The fungi are large and successful group 0f organisms. They are eukaryotic. They vary in size ranging from unicellular (yeast) to multicellular (toad stools; mushroom; puff balls; etc.). They occupy a very Wide range 0f habitats both aquatic and terrestrial. Fungi include the numerous moulds which grow on damp organic matter such as bread, leather, decaying vegetation and dead fish), the unicellular yeast which are abundant on the sugary surface of ripe fruits and many parasites of plants. Mycology is the study of fungi.

GENERAL CHARACTERISTICS They lack chlorophyll and are therefore nonphotosynthetic. They are therefore heterotrophic. They have non-cellulose cell wall. They have no true roots; no true stem and leaves. Their vegetative body is called mycelium (plural: mycelia) and consists of hyphae. The hypha may be separate, that is, having cross-walls (eg. Penicillium) or aseptate that is without cross-walls (eg. Mucus). They reprodUce by means of spores. They are either parasitic or saprophytic. Examples include, penicillium; mucus; mushroom; bracket fungi;




KINGDOM: PLANTAE (PLANTS)
     These are autotrophic eukaryotes which have mainly become adapted for life on land. The only other autotrophic eukaryotes are algae which are specialized for life in water. Members of this kingdom are found in all parts of the world. They exist in rivers, in lakes; sea; land; etc. The kingdom is classified into six phyla.


GENERAL CHARACTERISTICS OF KINGDOM PLANTAE
    They are multicellular organisms. They have cell wall made of cellulose. They have chlorophyll and hence, can manufacture their own food. They are eukaryotic and autotrophic.




KINGDOM: ANIMALIA (ANIMALS)
       Animals make up one of the four eukaryote kingdoms. They are all multicellular since the animal like unicellular organisms are placed in the kingdom protoctista. They are heterotrophic. They differ from fungi, which are also multicellular, heterotrophic and eukaryotes in the way they obtain their food. Fungi digest food outside their bodies and absorb the products whereas animal nutrition typically involves ingestion followed by digestion inside the body. Any indigested food is egested. A number of feeding habits have developed, including carnivorous, herbivorous, omnivorous and parasitic modes of life. Whereas fungi grow on their food, animals have to seek it. If they do, this requires locomotion, and this in turn requires a nervous system with sense organs and effectors. The kingdom is divided into nine phyla.


GENERAL CHARACTERISTIC OF THE KINGDOM, ANIMALIA
      They are multicellular and eukaryotic, they are non-photosynthetic (i.e. no chlorophyll). They undergo heterotrophic nutrition. They do not have cell wall. Their life processes are normally controlled by the central nervous system.





I Hope You Have Read And Understood.
Now Answer The  Questions Below;

THE FIVE KINGDOMS AND THE HIERARCHY OF CLASSIFICATION

1. List the general characteristics of organisms in the following kingdoms and name one organism in each kingdom:
i. Prokaryotes
ii. Protoctista
iii. Fungi

2. State three characteristics of each of the organisms found in any four of the kingdoms into which living organisms are classified. Give two examples of organisms for each kingdom.

3. State four reasons for classifying organisms.

4. Briefly explain classification in Biology.

5. State two importance of classification.

6. Name two scientists who contributed to the development of biological classification.

7. Why are organisms classified?

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