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DESCRIPTION AND GROUPS OF MICRO-ORGANISM
Micro-organisms otherwise called microbes or germs can be defined as living things which cannot be seen with unaided eye but by the use of microscopes.
They exist almost everywhere, in water, air, soil, surface of objects, as well as on and within living organisms. They are carried by air currents from the earth’s surface to the upper atmosphere. They occur most abundantly where there is food, moisture and adequate temperature for their growth.
It was the invention of microscope that opened the gateway to the world of these minute living organisms. The first person to discover microbes was a Dutch man called Anthony Leeuwenhoek (1632-1723). Using a simple microscope, he was astonished to discover that rain water that had been collected from pools was full of little organisms.
GROUPS OF MICRO-ORGANISMS
Micro-organisms include all viruses, bacteria and the protists. Others are the cyanobacteria, certain fungi and algae.
1. BACTERIA: These are minute unicellular organisms or simple association of similar cells which multiply by binary fission. Most bacteria cells range between 0.2 µ-2µ in diameter and 0.0005mm-0.002mm long. Each bacterium cell has a cell wall with cytoplasm. There is no well defined nucleus. Consequently, they are prokaryotic organisms.
There are different kinds of bacteria showing a range of shapes. Certain kinds of bacteria have long thread-like structures called flagella which assist in locomotion. Bacteria with spherical shape are referred to as cocci (singular-coccus). There are several forms as shown on the next page.
2. Streplococci- These are arranged in chains. They cause a sore throat.
3. Staphylococci- These stick together to form irregular bunches. They cause boils.
4. Diplococci- They occur in pairs. e.g. pneumococci, which cause pneumonia.
5. Bacilli- They is rod-shaped. They cause typhoid fever.
6. Spirilla (singular = spirillum)- These are rod-shaped bacteria twisted into a spiral shape.
7. Spirochaetes- These are also spiral in shape but are more flexible and slender with helically coiled structure e.g., Treponema pallidum, which causes syphilis.
8. Vibrios- These are comma-shaped bacteria e.g., Vibrio cholerae, which causes cholera.
2. VIRUSES: Viruses are a large group of pathogens whose presence is felt only when they are in contact with living cells. They are very small and vary between 0.1µ-0.25 µ in diameter. The largest virus is less than one-fourth the size of a typhoid bacterium.
A virus consists of a nucleic material, either DNA or RNA, enclosed within a protein coat. Outside living organisms, they are like complex chemicals.
3. PROTISTS: These are single-celled animals, mostofwhich are only visible by means of microscope. They are common in fresh water and moist soils. Examples include Euglena, Paramecium, Trypanosoma, Plasmodium, etc.
4. FUNGI: They are diversified in form. The blue and green growth on oranges, lemons, cheese and the white/grey growth on bread are usually signs of fungal infections. Fungi feed saprophytically. Examples of fungi include Mucor, Rhizopus, Penicillium, Aspergillus, etc.
5. ALGAE: Most algae are unicellular and very small. They have chlorophyll. They occur abundantly in water, moist soils, bark of trees, stones, etc. Free floating microscopic algae are referred to as phytoplanktons and they form the major food of aquatic animals. Examples of unicellular algae include Chlamydomonas and Protococcus.
EVALUATON
1. What are microorganisms
2. List five groups of microorganisms with two examples each
ASSIGNMENT
1. Who was the first person to discover microbes? a) Louis Pasteur b) Anthony Leeuwenhoek c) Robert Koch d) Alexander Fleming
2. Microorganisms are defined as: a) Living things that can only be seen with the naked eye b) Living things that cannot be seen with unaided eye but by the use of microscopes c) Only single-celled organisms found in water d) Only disease-causing organisms
3. Which of the following is NOT a group of microorganisms? a) Bacteria b) Viruses c) Mammals d) Fungi
4. Bacteria are considered prokaryotic organisms because they: a) Have a well-defined nucleus b) Do not have a cell wall c) Do not have a well-defined nucleus d) Are multicellular
5. Which type of bacteria are arranged in chains and cause sore throat? a) Staphylococci b) Streptococci c) Diplococci d) Bacilli
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