Exam Lessons

Identification of Micro-organisms in the Air, Pond Water, River, Stream

Micro-organisms in the Air

Micro-organisms commonly found in the air are: Bacteria, Virus and Fungi. These microbes do not grow in the air but are present as spores in dust and water droplets in the air. These  spores are light and easily dispersed by air movement. When these spores land on suitable substrate, they germinate, multiply and produce more spores. Micro-organisms found in the air and examples:

(a) Bacteria: Examples – Pneumococci, Staphylococci, Streptococci, Bacillus anthracis, which causes anthrax in herbivores.

(b) Virus: examples – Influenza, Polio virus, common cold virus, measles virus.

(c) Fungi: Examples – Sacromyces (yeast), Rhizopus nigricans (bread mould), Penicillium (blue-green mould) Aspergillus etc.

Bacterial Cultures

Colonies of the bacteria known as Escherichia coli (larger, pink) and Proteus vulgaris (smaller, brown) grow side by side in this petri dish culture. Under normal circumstances both of these bacteria harmlessly inhabit the human intestines and aid in digestion, but can become pathogenic and cause infections, such as urinary tract infections. Scientists and doctors grow cultures of bacteria and study their characteristics in order to learn about bacterial diseases and disease prevention.

Micro-organisms in Water

Micro organisms found in water are commonly known as plankton. Aquatic environment, unlike atmosphere are rich in organic and inorganic nutrients. They can be found in all types of water habitat viz: wells, ponds, lakes, streams, rivers and seas.

All microbes found in water can be grouped into three as follows:

  1. Natural water micro-organisms: these are microbes that are naturally found in aquatic habitats.
  2. Soil micro organism ( washed into the surrounding water bodies during heavy rains)
  3. Sewage micro-organisms

Micro-organisms in Water and their Examples

  1. Bacteria: Examples – aquatic species of coccus, Baccillus, Pseudomonas, Azobacter, Thiobacillus, Sarcinina, spirillum, Micrococcus, Vibro and Spirochaeta. These bacteria are either heterotrophic, autotrophic and chemotrophic.
  2. Blue green algae:Examples; oscillatoria, nostoc, anabaena,
  3. Protists: These are autotrophic diatoms e.g. chlamydomonas, cholera and some species of euglena as well as heterotrophic amoeba and paramecium.
  4. Algae: These are located close to the shore of where they form thick green floating mesh e.g. spirogyra, volvox etc. Algae arte major part of primary producers in the aquatic habitat since they contain chlorophyll and can photosynthesis.

Micro-organisms in Our Bodies

Various parts of human body such as the skin, hair, mouths, nose, ears, under the nails, our teeth etc to different micro-organisms as well as serve as entrance for these micro-organisms into our bodies.

Millions of micro-organisms living inside and outside the human body. These microbes are non-pathogenic. They are regarded as the normal micro flora which plays importance role in the body.

This normal micro flora prevents pathogen from invading the body as well as secretes certain substances that inhibits or kills some other pathogens.  Weakened immune systems , indiscriminate use of antibiotics, unhygienic practices like smoking and intake of alcohol malnutrition, stress etc could make non-pathogen to become pathogenic harmful to the body as the normal micro flora become disturbed.

Pathogens harm the body by using up the hosts’ nutrients thereby starving the tissue of the host.

Through their actions they damage tissues of the affected part of the host as well as produce toxins that negatively affect the functioning of particular organs or body systems of the individual.

Entry of Micro-organisms into Our Body

Micro-organisms enter the human body through:

  1. Buccal cavity:The food we eat and the water we drink. Such pathogen cause air borne infection like tuberculosis cause by mycobacterium tuberculosis
  2. The nose: Air we breathe in, into the respiratory system such virus normally cause cold.
  3. Damaged skin:Cuts or bruises on the skin into the blood stream Telamus. fungi infection, leading to ringworm on the head, foot etc.
  4. Oesophagus:Contaminated food or drinking water.
  5. Direct contact:Skin surfaces e.g. fungal infections which result in ringworm of the head and foot.

Micro-organisms in Food

The physical and chemical properties of any food determine the type of micro-organisms that will grow and reproduce. When micro-organisms or their spores get in contact with food, such food gets contaminated and when consumed man can have adverse effect on the individual.

Carriers of Micro-organisms

Apart from the various means through which microbes get into our body already discussed, there are certain organisms that carry micro-organisms that can affect man negatively about. These organisms are called Careers are usually insects and mammals. The hairy nature of the insect body traps the microbes and gets carried from place to place. The natural habitats of these insects include latrines, food stores, dung hills and other similar places where microbes abound. The careers pick up the pathogens and bring them to exposed human food. As they land on these exposed food to feed on them, the microbes are transferred to the food which could be eaten by man and consequently bring about infection and diseases. These careers are called Vectors. The pathogen neither grow nor affect them adversely hence, they are called Vectors. Vectors are primary to the pathogen while man is the secondary Host.


  1. What are careers? Give two examples.
  2. State the habitat of the career named above.

Location of Micro-organisms in Carriers

Organisms that carry micro-organisms are called vectors. Diseases caused by a carrier do not affect the vector that carries them.

The micro-organism found in vector lives in them temporarily for the purpose of developing to the stage where they can effectively infect man. Thus the pathogens have two hosts. This phenomenon is killed alternation of hosts. The vector is the primary host while man is the secondary host of the pathogen. Mosquitoes, Tsetse fly are examples of vectors of microorganism that do not develop inside the housefly. Instead the body of the housefly’s body “collects” micro-organisms as it perches on exposed human food to feed on it, the microbes (bacteria) falls off its body onto the food which causes disease unto man when contaminated food is eaten.

Through biting and sucking man’s blood, Anopheles Mosquito transmits a protozoan – plasmodium into mans blood causing disease – malaria. The pathogen is in the gut of the insect and as it feeds on the blood of man, it deposits it into man.


  1. Define the following terms: (i) natural microflora (ii) pathogen (iii) careers (iv) vectors
  2. Name and describe the two methods by which pathogens are carried from place to place.
  3. List the important groups of micro-organisms and give one example from the group.
  4. What is culture?
  5. Outline the steps you will take in preparing a culture solution.
  6. (a) What do you understand by micro-organisms? (b) Describe how micro-organisms enter our bodies with examples and steps preventing them. (c) List the groups of micro-organism with examples.
  7. (a) List micro-organisms found in water with examples. (b) Micro-organism in 2a can be grouped into 3, name these groups with short explanations. (c) A group of aquatic micro organisms are known as primary producers explain.
  8. (a) What is culture? (b) What steps are entails in preparing a culture solution (c) Outline precautions to observe in preparing a culture solution.
  9. (a) Describe an experiment to show that atmospheric Air contains micor-organisms. (b) What are the functions of natural normal micrflora in and on human body? (c) List two insects and three mammalian vectors, stating the following for each organism: (i) micro-organisms (ii) Disease caused (iii) possible control of spread
  10. Define the following terms: (a) natural microflora (ii) pathogen (iii) careers (iv) vectors (b) Write short notes on the importance of micro-organism to man in the area of (i) medicine (ii) agriculture

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