What are Microorganisms?
MICRO-ORGANISMS
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Very small Living plant or animal
- They are living organisms of very small sizes. They are so small that they cannot be seen by the naked eye.
- We would require a microscope or magnifying glass to see them.
Example: Bacteria, Fungi
- There are four major groups:
Bacteria
Fungi
Protozoa
Algae
Viruses are also microscopic but are quite different from other microorganisms. They grow only inside cells of other plants and animals.
Different types of microorganisms:
| Type of Microorganisms | Description | Examples |
| Bacteria | They are small single-cell organisms having cell walls but no nucleus. They can be spherical, spiral or rod-shaped. | Lactobacillus, Rhizobium |
| Fungi
|
They are microorganisms containing a nucleus. They look like plants but cannot prepare their own food. They do not contain chlorophyll and cannot photosynthesise. | Yeasts, moulds |
| Protozoa | They are animal-like microorganisms. Most of these are parasites and feed on other organisms. | Amoeba, Paramecium |
| Algae | They are plant-like microorganisms. They contain chlorophyll and do photosynthesis to make food. | Chlamydomonas, Spirogyra |
Bacteria
Paramecium
Amoeba
Spirogyra Clamydomonas
Virus
- These are microorganisms that reproduce only inside cells of other plants and animals.
- These are agents of various diseases like cold and flu (Influenza)
- Viruses also cause serious diseases like Polio and Chickenpox.
Important points about Microorganisms
- Microorganisms can be single-celled or multicellular.
- Some are made of single cell (unicellular) example: Protozoa, bacteria.
- Some are made of many cells (multicellular) example: Algae, Fungi.
- They live in all types of environments from ice-cold climates to hot springs and deserts to marshy lands.
- Some live inside other organisms including humans.
Microorganisms and Us
- Microorganisms are both good and bad for us.
- Some are beneficial to us while others are harmful and cause diseases.
Friendly Microorganisms
- They help in making curd, bread and cake. Milk is converted to curd by the multiplication of bacteria.
- Bacteria and yeast also help in the fermentation of rice idlis and dosa batter.
- Yeast is used for making bread, pastries and cakes.
- They clean up the environment. For example, breaking down organic waste into harmless and reusable substances by bacteria. They also increase soil fertility by fixing nitrogen.
Commercial use of Microorganism
- They are used for the commercial production of alcohol, wine and vinegar.
Medicinal uses of Microorganisms
- Some microorganisms are also used as medicines. Examples Antibiotics and Vaccines.
Antibiotics
- There are some microorganisms that are good for us and fight against harmful microorganisms.
- Antibiotics are medicines that stop the growth of disease-causing microorganisms.
- Example: Penicillin, Streptomycin, Tetracycline.
Vaccine
- Vaccines are prepared from microorganisms.
- These vaccines help the body in making antibodies that fight these microorganisms and prevent diseases in future.
- Examples: Polio drops given to children up to the age of 5.
- Vaccine for Cholera, Hepatitis, smallpox etc.
Harmful Microorganisms
- Some microorganisms harm in different ways.
- Some cause diseases in humans, plants and animals. Such disease-causing microorganisms are called Pathogens.
- Some spoil food, clothing and leather.
Disease-causing microorganisms in Humans
Diseases caused by microorganisms in animals
Diseases caused by microorganisms in Plants
Food Poisoning
- Food poisoning could be due to the consumption of food spoilt by some microorganism.
- Microorganisms that grow on our food sometimes secret toxic substances.
- These make food poisonous causing serious illness and even death.
Food Preservation
- It means preventing food from spoiling and getting rotten.
- It is done by adding preservatives for example salt, sugar etc to food.
Preservation by common salt
- Common salt is used on meat and fish to prevent the growth of bacteria.
- It is also used to preserve fruits such as raw mangoes, lemon and amla.
Preservation by sugar
- Sugar is used in Jams, Jellies and squashes.
- Fruits that are preserved in the form of jams and jellies are Apple, Mango, Strawberry, Guava, Orange etc.
- Sugar inhibits the growth of bacteria that spoil the food.
Preservation by oil and vinegar
- Oil and vinegar are used to preserve pickles.
- Vegetables, fruits, fish and meat are preserved by this method.
Heat and cold treatments
- Milk is boiled to kill microorganisms so that the milk can last longer.
- Low temperatures inhibit the growth of microbes. This is why food is stored in a refrigerator.
- Pasteurisation: In this process milk is heated to 70oC for 15 – 30 sec and then suddenly chilled and stored. This prevents the growth of microbes. This process was discovered by Loius Pasteur.
Chemical treatment
- Chemicals such as Sodium Benzoate and Sodium Metabisulphite are used as common preservatives.
- These are also used in jams and squashes to check their spoilage.
Storage and Packing
- Nowadays, dry fruits and even vegetables are sold in sealed airtight packets to prevent attacks of microbes.
Nitrogen Fixation
- The process by which atmospheric nitrogen is converted to Nitrates and Nitrites which can be used by plants is called Nitrogen Fixation.
- These nitrogen compounds are used for the synthesis of plant protein.
- Nitrogen can be fixed by
- Nitrogen-fixing bacteria in the soil.
- Rhizobium bacteria – which lives in the root nodules of leguminous plants such as beans and pulses.
- By Blue-green algae
- By Lightening
The atmosphere has 78% Nitrogen. This nitrogen gets fixed by
- Rhizobium bacteria
- Blue-green algae
- Lightening
Thus, nitrogen in the air gets converted into Nitrogen compounds, which are nutrients for the soil.
Plants consume these nutrients.
The animal eats plants and gets Nitrogen.
Both plants and animals die/excrete waste.
Bacteria convert the waste back to nitrogen.