Concept of Classification-FORM ONE

Concept of Classification

The Concept of Classification

Explain the concept of classification

Have you ever visited a library? How are the books arranged and kept? Are they arranged randomly or systematically? Obviously the books are arranged systematically in the shelves. Science books are kept separately in their respective shelves. Science books are kept separately from social or commercial books. Biology books are separated from physics books or chemistry books. Likewise, in the shop, laboratory or pharmacy items are sorted and placed on the basis of their similarities.

In the world, there are numerous varieties of living organisms.These organisms do vary in size, structure, shape, habitat, mode of feeding and even mode of reproduction. The organisms can be sorted out and placed into different groups based on their similarities. The system of sorting out and placing organisms into different groups on the basis of their similarities and differences is called classification.

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The Importance of Classifying Living Things

Explain the importance of classifying living things

The following are importance of classification

1. Classification makes the study of living things easy
2. Classification makes communication easy among biologists from different parts of the world
3. It provides good organized system in which a newly identified organism can be easily fitted in future.
4. It makes it easier to identify organisms
5. It can be used to predict characteristics that are present in the members of the same group.

Classification Systems

Types of Classification Systems and Their Differences

Outline types of classification systems and their differences

There are two types of classification

1. Artificial classification
2. Natural classification

Artificial classification. An artificial classification is based on one or a few easily observable characteristics and usually designed for practical purpose with an emphasis on convenience and simplicity. In this type of classification, unrelated organisms are often placed in the same group while closely related organisms are often placed in different groups.Linnaeus included all

Linnaeus included all worm-like organisms in a single group, the vermes. This included wide a range of animals as from nematodes, earthworms to snakes. This was an artificial classification since it did not consider natural relationships such as the fact that snakes have backbones and earthworms do not have. Thus, snakes have more features in common with vertebrates than with worms.

Bats and birds would be placed in the same group because all have the ability to fly since they posses wings. But bats share many features with mammals. They have features like hair, mammary glands, sweat glands and different types of teeth which are characteristics of mammals. Therefore, bats are more related to mammals than birds.Natural

Natural system of classificationThis type of classification system tries to use natural relationships between organisms. It considers many features in common including internal as well as external features.Similarity of embryology, morphology, anatomy, biochemistry cell, structure and behaviour are all considered relevant. It is based on evolutionary relationship in which organisms belonging to the same group are believed to have a common ancestor.

Characteristic features which show homology are distinguished from those which show analogy. Example the fore limbs of mammals, whales, birds and bats have the same basic pattern and similar bone arrangement, i.e. homologous. This suggests that these organisms are coming from the same ancestor and that can be placed in the same group.

The wings of birds and grasshoppers are analogous. The wings of birds have internal skeletons while the wings of grasshoppers do not have bones but they perform similar function. These organisms cannot be placed in the same group since they are different in many ways.

Merits and Demerits of Each Type of Classification System

Explain merits and demerits of each type of classification system

Advantages of artificial system of classification

1. It is easy to classify organisms since it is based on few observable characteristics.
2. It does not take much time to classify organisms based on this system (not time consuming).
3. It does not need expertise (even a layman can do).
4. It is relatively stable i.e. not easily changing from time to time.

Disadvantages of artificial system of classification

1. It tends to place closely related organisms into different groups instead of being grouped together e.g. a bat can be placed in a group of birds instead of mammals.
2. Different or unrelated organisms may be placed in the same group e.g. bats placed in a group of birds, worms placed with snakes in the same group
3. The system does not provide enough information about its members.
4. It is difficult to incorporate additional information.

Advantages of natural system of classification

1. Closely related organisms are placed in the same group.
2. It reflects evolutionary relationships.
3. Unrelated organisms cannot be placed in the same group.
4. It makes it easy to incorporate additional information.

Disadvantages of natural system of classification

1. It is difficult since it considers many features.
2. It requires expertise i.e. more knowledge about an organism.
3. It is time consuming.
4. It is relatively unstable i.e. it changes from time to time.
5. It is more expensive since more data are required.

Differences between natural classification and artificial classification

Artificial classification	Natural classification
(i) Considers few features in common	Considers many features in common
(ii) Does not reflect on evolutionary relationships	Reflects on evolutionary relationships
(iii) It is easy to classify	It is difficult to classify
(iv) Not time consuming	It is time consuming
(v) Does not require expertise	Requires expertise
(vi) New information cannot be added	New information can be added.

Major Groups of Living Things

Major Groups of Living Things

Mention major groups of living things

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

Outline 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:

1. Must have many features in common.
2. Must be able to breed one another to produce fertile offspring.
3. 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 nomen-clature. 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 hand written.
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 1

Examples of scientific names

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
Amoeba	Amoeba	proteus
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

Viruses

Viruses were discovered by a Russian botanist D. I. Ivanovsky and a Dutchman Beijerink. In 1852 Ivanovsky prepared an infectious extract from tobacco plants that were suffering from mosaic disease. When the extract was passed through a filter able to prevent the passage of bacteria, the filtered fluid was still infectious. 1898 Beijerink gave the name “virus” (in latin means, “poison”) to describe the infectious nature of certain filtered plant fluids.

General and Distinctive Features of Viruses

Explain general and distinctive features of viruses

Characteristics of Viruses

1. They are the smallest living organisms ranging from 20-30nm. On average, they are about 50times smaller than bacteria.
2. Viruses do not have cellular structures, which mean that they lack certain important organelles like nucleus, cytoplasm, golgi bodies, etc.
3. They can only reproduce inside the living cells hence they are parasitic.
4. They have a simple structure consisting of either DNA or RNA but not both, surrounded by a protein or lipoprotein coat.
5. They can be described as living or non-living.
6. They are highly specific to their hosts i.e. each virus recognizes only certain types of cells.
7. Viruses are capable of replicating themselves only when they are inside the host cell.

Viruses as living things

1. They possess genetic material (RNA or DNA).
2. They reproduce when they are in the host cell (replication).
3. They are capable of identifying their hosts and attack them.
4. They can undergo mutation (they mutate) i.e. they undergo different changes in shape.
5. Like other parasites, they are specific to host.

Viruses as non-living things

1. They can crystallize outside the host.
2. They are metabolically inert in isolation.
3. They are non-cellular i.e. they lack cell organelles.
4. They do not perform necessary life processes such as respiration, excretion nutrition etc.

The Structure of Viruses

Describe the structure of viruses

Generally viruses have a very simple structure consisting of the following:

1. RNA or DNA which may be single stranded or double stranded. They form a structure called core.
2. A protective coat of protein surrounding the core called capsid.
3. A nucleocapsid which is a combined structure of core and capsid.
4. Envelope – an additional layer of lipoprotein layer around the capsid.
5. Capsids are made up of identical repeating units known as capsomeres.

Bacteriophage

Bacteriophage is a virus that attacks and kills bacteria. Some of them have head with a tail sheath.

Bacteriophage

Advantages and Disadvantages of Viruses

Outline advantages and disadvantages of viruses

Advantages of viruses

1. Viruses are used in developing vaccines, for example, vaccines for measles, polio and rubella are made from viruses that have been attenuated (weakened).
2. Viruses are used as biological weapons to kill organisms.
3. They are used as vectors in genetic engineering to transfer genes from one organism to another for improving or treating the defective genes.
4. Bacteriophages are viruses that attack bacteria and hence they help in controlling infections and diseases.
5. Viruses are used as biological weapons in wars and in biological pest control.

Disadvantages of viruses

1. Most viruses cause diseases to both plants and animals. Plant disease such tomato mosaic, cassava mosaic and tobacco mosaic; and animal diseases e.g. measles, small pox, poliomyelitis and yellow fever are caused by viruses.

Kingdom Monera

This kingdom is made up of organisms known as bacteria (singular: bacterium). They are the most ancient and smallest organisms with a cellular structure. They are mainly single celled. Bacteria occupy many environments such as soil, dust, water and in the bodies of plants and animals

Some bacteria are found in hot springs where temperatures are 78ºC or more. Others can withstand very low temperatures. Some are found in very deep cracks in the ocean floor, at very high temperatures, about 360ºC (extreme thermophiles).

General and Distinctive Features of the Kingdom Monera

Explain general and distinctive features of the kingdom monera

General characteristics of the kingdom monera

1. They are mainly unicellular and very small.
2. They are all prokaryotic (nucleus not bound by membrane)
3. They reproduce by binary fission.
4. Some members of the kingdom are autotrophs while others are heterotrophs
5. They have cell wall made up of protein material and sometimes lipids.
6. Some bacteria form spores during adverse conditions i.e. extreme conditions e.g. high or low temperatures, drought etc. The spores allow them to survive as they have very thick resistant walls.
7. Some are aerobes while others are anaerobes.
8. The genetic material (DNA) is scattered in the cytoplasm and they lack internal membrane bound organelles such as mitochondria, chloroplasts, golgi bodies etc.

Structures of the Representative Organisms of the Kingdom Monera

Describe structures of the representative organisms of the kingdom monera

General structure of the bacteria

1. Bacteria have strong and rigid cell walls due to the presence of murein. The wall prevents the cell from bursting when it absorbs much water (as a result of osmosis).
2. Bacterial cells are bounded by partially permeable membranes.
3. Bacteria possess capsules which are slimy or gummy.They have flagella which aid motility of the bacteria. Motile bacteria can move in response to a certain stimulus i.e. tactic movement. Flagella can easily be seen by electron microscope.
4. They have small self replicating circle of extra DNA called a plasmid.

General structure of bacterium

Forms of bacteria

Bacterial shape is an important aid to classification. There are four main shapes

Coccus (plural: cocci)

They are spherical in shape and can be of the following types.

• Micrococcus – exist singly. They cause sore throat.

• Diplococci - this type of bacteria exist in pairs. The pneumococci (Diplococcus pneumoniae) are the only members. They cause pneumonia.

• Streptococci – this type of bacteria stick together and form a chain. Most of them infect upper respiratory surface and cause diseases e.g. sore throat.

• Staphylococci – These bacteria form a grape like bunch. They cause boils, pneumonia, food poisoning and other diseases.

Bacilli (singular: bacillus)

These are rod shaped bacteria. They can be:

• Single rods, for example, Escherichia coli commonly living in the gut and Salmonella typhiwhich cause typhoid fever.

• Rods in chain, for example, Azotobacter, a nitrogen-fixing bacteria, and Bacillus anthraciswhich cause the disease anthrax.

• Bacilli with endospores showing various positions, shapes and sizes of spores. They can be:

1. Central, not swollen e.g. Bacillus anthracis causes anthrax
2. Spherical spore, terminal swollen e.g. Clostridium tetani causes tetanus
3. Sub-terminal, swollen e.g. Clostridium botulism causes botulism.Spores may also be central

Spirilla (singular: spirillum)

These are spiral-shaped bacteria e.g. Treponema pallidum which causes syphilis