What is classification?
It is the system of sorting out and placing organisms into different groups on the basis of their similarities and differences.
Types of classification:
There are two types of classification:
- Artificial classification/system.
- Natural classification/system.
In this system only one or a small number of features are considered e.g. birds and bats all have the ability to fly. So by using this system, one can place the birds and bats in one group. Just by considering one feature that is the ability to fly. But in reality, birds and bats are classified into different groups.
Birds -> Aves.
Bats -> Mammals.
In this system, organisms are placed in their natural groups by:
- Considering many features in common.
- Characters that show:
Homology- Similarity of origin.
Analogy- Similarity of use.
Example of Homology:
The arms of a man, forelimbs of whales and wings of birds or bats are homologous because they have same order and pattern of bones. So these show that they have the same origin.
Example of Analogy:
The wings of birds and grasshoppers are analogous, because birds have internal skeleton (endoskeleton) and grasshoppers have external skeleton (exoskeleton). So these wings perform the same function but have different origins.
Importance of classification:
- It helps us understand the characteristics of living things.
- It enables man to identify and name numerous organisms.
- It brings together living organisms with similar characteristics but separates those with different features.
- It helps man arrange information about living organisms in an orderly manner to avoid confusion.
- It makes the study of living organisms very easy.
- It provides an organized system into which newly identified similar organisms can be fitted in future.
Advantages of Artificial classification.
- Based on easy and simple characteristics.
- Uses convenient and readily observable characteristics.
- Based exclusively on arbitrary criteria.
Disadvantages of Artificial classification.
- Unrelated organisms may be placed in the same group.
- Tends to place closely related organisms into different groups instead of being grouped together.
Advantages of Natural classification.
- Avoids confusion
-Unrelated organisms can’t be placed in the same group.
-Closely related organisms with common characteristics features are placed in the same related group.
-Because it uses same system of naming organisms.
Disadvantages of Natural classification.
It is not based on easy and simple characteristics but on evolutionary relationships.
Is a scientific system of naming living organisms whereby each organism is assigned two names. The first name being the Genus and the second name is the species.
Note- Bi means two, Nomino means name.
So Binominal means two names.
Rules of binominal nomenclature:
- Only the first letter of the genetic name is capitalized and then the whole genetic name is underlined eg. Homo.
- The first letter of the species name is never capitalized, and then the whole species name is underlined eg. sapiens. So the scientific name for man is Homo – genus, sapiens – species.
- If the scientific name is written in italics, then it should never be underlined, but other rules remain the same.
Eg: Homo sapiens (Romanic)
Homo sapiens (Italic)
Examples of scientific names:
Man – Romanic:Homo sapiens.
Elephant – Romanic:Loxodorita africane.
Maize – Romanic:Zea mays.
Dog – Romanic:Canis familiasis.
Lion – Romanic:Panthea leo.
Ranks of classification (Toxonomic.)
Ranks are the groups into which organisms are placed as the matter of convenience based on easily observable features, that are shared in common for group identification.
These are seven major ranks of classification, they are:
Genus:Is a group of organisms with a large number of similarities but unable to interbreed successfully.
Species:Is a group of organisms which are capable of interbreeding together and produce fertile offsprings.
THE MAJOR KINGDOMS.
There are five major kingdoms of living things. These major kingdoms exclude a virus. Because the virus is between living and non-living things. The major kingdoms are:
- Kingdom Monera.
- Kingdom Protoctista.
- Kingdom Fungi.
- Kingdom Plantae.
- Kingdom Animalia.
Is a chemical between living and non-living things.
Characteristics of a virus:
- They are living and non-living things.
- They are RNA or DNA.
- They can multiply only in living cells.
- Each virus is specific in its host and even of the type of a cell within its host.
- They are the smallest living or non-living organisms about 50 times bacteria.
- They can only be seen under electronic microsopes.
Economic importance of virus.
- They cause plant diseases.
- They cause animal diseases.
- They attack and kill bacteria.
- Used in making vaccines etc.
Kingdom Monera (Bacteria)
- They are unicellular and very small organisms.
- They have cell wall made up of polysaccharides, cellulose, fat, proteins and chitin.
- They store food in form of glycogen, fats, proteins, sometimes sulphur.
- They are heterotrophic organisms.
- They are obligate bacteria’s- respires aerobically. Facultative bacteria- respire anaerobically, micro-aerophilous- respire in very low oxygen.
- They are capable of producing toxins which can poison other organisms.
- Bacteria can grow best in 30º-37ºc, 15º-20ºc, -2º – -9ºc, 60ºc and above.
- They reproduce by binary fission.
- They live in soil, dust, water, air, animals and plants. In addition to that, bacteria’s are enormous e.g. in 1cm3 of fresh milk, it contains more than 300,000,000 bacterias.
- Together with fungi, they cause decay of organic materials and hence recycling of nutrients.
- They are prokaryotic.
Forms of bacteria.
Coccus:It causes sore throat.
Streptococcus:Causes sore throat.
Bacterium:Bacillus anthrax:Causes anthrax.
Economic importance of bacteria:
1. Production of antibiotics.
- Used in sewage (They decompose pollutants)
- Used in cheese and butter making.
- Used in vinegar and alcohol production.
- Used in fermentation process etc.
Members of these kingdom resembles the ancestors of plants, animals and fungi. These are the algae, protozoa etc. In protozoa we have amoeba and paramecium etc. other members of this kingdom are euglena and trypanosome. Algae contains red, brown and green algae.
General characteristics of Kingdom Protoctista:
- Are eukaryotic organisms.
- Many are unicellular.
- It includes organisms which resembles early plants (algae), early animals (protozoa) and early fungi (Oomycetes).
- Are the links between prokaryotes and modern eukaryotes.
- They locomote by the use of cilia or flagella.
- They have a contractile vacuole for excretion.
- They feed holophytically (This means that they feed autotrophically e.g. euglena and heterotrophically e.g. amoeba and paramecium.)
- They reproduce by binary fission and multiple division which means sexual and asexual.
- They contain a clear and visible nucleus.
- The locomotary structures are:
Economic importance of Kingdom protoctista.
- Causes diseases e.g. sleeping sickness in man by a trypanosome transmitted by a vector called tsetse fly.
- Plasmodium causes malaria in man transmitted by female anopheles mosquito.
There are of 4 species: