General Science - Biology: Micro organisms (Notes)

Micro organisms are classified into four major groups. These groups are bacteria, fungi, protozoa and algae.

Viruses : They reproduce only inside the cells of the host organisms which may be bacterium, plants or animal.
- Common cold, influnenza and most coughs are caused by viruses.
- Serious diseases like polio and chicken pox are also caused by viruses.
- Micro organisms may be single celled like bacteria, Some algae and protozoa.

Multicellular such as algae and fungi.

- Micro organisms like amoeba can live alone, while fungi and bacteria may live in colonies.

Friendly Micro Organisms

- Making of curd and breed:-milk is turned into curd by bacteria. The bacterium lacto bacillus promotes the formation of curd.
- Yeast reproduces rapidly and produces CO2 during respiration. Bubbles of the gas fill the dough and increase its volume; this is the basis of the use of yeast in the booking industry for making breads, pastries and cakes.
- Yeast is used for commercial production of alcohol and wine. For this purpose yeast is grown as natural sugars present in grains like barley, wheat, rice, crushed fruit juice etc.
- This process of conversion of sugar into alcohol is known as fermentation. Louis Pasteur discovered fermentation.

Medicinal Use of Micro Organisms

- The medicine which kills or stops the growth of diseases causing microorganism is called antibiotics.
- Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics. Which are made from fungi and bacteria.
- Alexander Fleming discovered penicillin.
- Antibiotics are not effective against cold and flu as these are caused by virus.

Vaccine

- When a disease carrying microbe enters our body, the body produces antibodies to fight the invader.
- The antibodies remain in the body and we are protected from the disease causing microbes. This is how a vaccine work.
- Several diseases including cholera, TB, small pox and hepatitis can be prevented by vaccination.
- Edward Jenner discovered the vaccine for small pox.

Increasing Soil Fertility

- Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich the soil with nitrogen and increase its fertility.
- These microbes are commonly called biological nitrogen fixer.

Harmful Microorganisms

- Microbial diseases that can spread from an infected person to a healthy person through air water, food, or physical contact are called communicable diseases. i.e.- cholera, common cold, chicken pox and TB.
- There are some insects and animals which act as carrier of disease causing microbes like house fly. Another is female anopheles mosquito which caries the parasite of malaria.
- Female aedes mosquito acts as carrier of dengu virus.
- Robert Koch discovered the bacteria (bacillus anthracis) which causes anthrax disease.
- It is a dangerous human & cattle disease.

Common Methods of Preserving Food in our Homes

- Chemical method : salt and edible oils are the common chemical generally used.
- Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the James and squashes to check their spoilage.

Preservation by sugar :

- Sugar reduces the moisture context which inhibits the growth of bacteria which spoil food.
- Use of oil and vinegar prevents spoilage of pickles become bacteria cannot live in such an environment.
- Pasteurized milk : the milk is heated to about 70oc for 15 to 30 seconds and then suddenly chilled and stored.
- This process was discovered by Louis Pasteur. It is called pasteurisation.

Some Common Plant Disease Caused by Microorganisms

Plant disease -Microorganisms -Mode of transmission
Citrus canker - Bacteria - Air
Rust of wheat  - Fungi -  Air, seeds
Yellow vein mosaic of bhindi  - Virus -  insect

Some Common Human Disease Caused by Micro Organisms

Human disease - Causative - Mode of transmission - Preventive measure microorganisms
Tuberculosis  - Bacteria  - Air  - Keep the patient in complete isolation.
Measles - Virus - Air  - Keep the person away from those of others
Chicken pox - Virus  - Air/contact belonging of the patient
Polio  - Virus - Air/Water  - Vaccination at suitable age.
Cholera  - Bacteria - water/food  - Maintain personal
Typhoid - Bacteria  - water hygiene and good sanitary habits. consumed properly cooked food and boiled drinking water vaccination
Hepatitis B -  Virus - Water  - Drink boiled drinking water vaccination.
Malaria - Protozoa  - Mosquito  - Spray insecticides and control breeding of mosquito.