Chapter 2 – Microorganisms: Friends and Enemies

Chapter 2 – Microorganisms: Friends and Enemies

 

1. What are Microorganisms? (What are Microorganisms?)

• Microbes are very small organisms that we  cannot see with our naked eyes.
• To see them, we  need a  microscope.

They are found everywhere – air, water, soil, inside and outside our bodies, and even in extreme conditions (hot springs, marshlands).

2. Types of Microorganisms

Microorganisms are mainly divided into four large groups:

1. Bacteria :

• • They are  single-celled.
  • Their shape can be different – round (coccus), stick-like (bacillus), spiral (spirillum).
  • Examples: Lactobacillus (yogurt maker), Rhizobium (nitrogen fixation).

1. Fungi:

• These are often multicellular, but some are also unicellular (such as yeast).
• They usually grow on rotten things.
• Examples: Yeast (alcohol, in bread making), Penicillium (antibiotic), mushrooms.

 

iii. Protozoa :

• These are mostly unicellular.
• These are usually found in water or moist places.
• Examples: Amoeba, Paramecium, Plasmodium (causative of malaria).

1. Algae :

• They are plant-like and can carry out photosynthesis.
• They are found in water.
• Examples: Spirogyra, Chlamydomonas.

1. Viruses:

• They are different from other microorganisms.
• They reproduce only inside the host cell  (e.g. bacterial, plant or animal cell).
• They appear to be lifeless when they are outside, but become alive as soon as they enter the living cell.
• They spread many serious diseases.
• Examples:  Colds, Flu, Polio, Measles, HIV, Corona Virus.

 

3. Friendly Microorganisms

Microorganisms are useful to us in many ways:

1. Making Curd and Bread:

• • A bacterium called lactobacillus turns milk into curd.
  • Yeast (a fungus) reproduces rapidly and releases carbon dioxide gas during respiration, which causes the dough to rise and make breads, pastries and cakes soft.

1. Production of Alcohol, Wine, and Acetic Acid:

• Yeast is used to convert sugar into alcohol. This process is  called  fermentation.
• Louis Pasteur discovered fermentation in  1857.

iii. Medicinal Use :

•  Antibiotics: These are medicines that inhibit or kill the growth of disease-causing microorganisms.
• Penicillin was the first antibiotic, discovered by Alexander Fleming in 1929  (it was derived from a fungus called Penicillium).
• Vaccine: Dead or weakened microorganisms that cause disease are inserted into the body. It helps the body make antibodies to fight disease  . Edward Jenner discovered the smallpox vaccine.

1. Increasing Soil Fertility:

• Some bacteria (such as Rhizobium that live in the roots of leguminous plants)  and blue-green algae  fix nitrogen from the atmosphere and add it to the soil, thereby increasing soil fertility.

1. Cleaning the Environment:

• Microorganisms decompose the organic waste of dead plants and animals into simple substances, providing nutrients to the soil and keeping the environment clean.

 

4. Harmful Microorganisms

Some microorganisms are harmful to us and spread diseases:

1. Disease-Causing Microorganisms (Pathogens):

• • Microorganisms that cause diseases  are called pathogens.
  • They can cause diseases in humans, animals and plants.
  •  Communicable diseases: Diseases that spread from an infected person to a healthy person through air, water, food, or direct contact.
    • Examples: cholera, common cold, chicken pox,  tuberculosis (TB).
  •  Disease Carriers: Some insects and animals carry such pathogenic microorganisms and spread them.
    • Examples: Female Anopheles mosquito (carrier of malaria), female Aedes mosquito (carrier of dengue), housefly (cholera, typhoid).

1. Common Human Diseases Caused by Microorganisms: Name of the disease | Type of Microorganism | Mode of Transmission | | :——— | :—————– | :————- | | Tuberculosis (TB) | Bacteria | Air | | Measles | Virus | Air | | Chicken Pox | Virus | Air/Direct Contact | | Polio | Virus | Air/Water | | Cholera | Bacteria | Water/Food | | Typhoid | Bacteria | Water | | Hepatitis A | Virus | Water | | Malaria | Protozoa | Mosquito (Carrier) |iii. Plant Diseases:

• Microorganisms also spread diseases in plants, reducing crop yield.
• Example:
  •  Citrus Canker: The bacterium is spread by air.
  •  Rust of Wheat: The fungus  is spread by air/seed.
  •  Yellow Vein Mosaic of Okra:  The virus is spread by the insect.

1. Food Poisoning:

• Some microorganisms grow in our food and  produce  toxic substances.
• Eating food containing these toxins can cause serious illness or even death.
• It is caused by eating stale or spoiled food.

5. Food Preservation

Ways to prevent food from spoilage by microorganisms:

1. Chemical Method :

• • Chemicals such as sodium benzoate and sodium metabisulfite  are used in jams, squashes, and pickles. These inhibit the growth of microorganisms.

1. Preservation by Common Salt:

• • Salt is used to preserve meat, fish, amla, mango and tamarind. It inhibits the growth of microorganisms.

iii.  Preservation by Sugar:

• Jams, jellies and squashes are preserved in sugar syrup. Sugar reduces moisture, which is necessary for the growth of microorganisms.

1. Preservation by Oil and Vinegar:

• The use of oil and vinegar in pickles inhibits the growth of microorganisms, as they cannot live in such an environment.

1. Heat and Cold Treatments:

• Heating: Boiling milk kills many microorganisms.
•  Pasteurization: Milk is heated at 70°C  for  15 to 30 seconds and then immediately cooled and stored. It inhibits the growth of microorganisms in the milk. This process was discovered  by Louis Pasteur.
• Cooling: Refrigeration does not spoil food quickly because the growth of microorganisms slows down at low temperatures.

1. Storage and Packing:

•  Dried fruits and vegetables are sold in airtight packets to protect them from microorganisms.

6. Nitrogen Cycle

• The atmosphere consists of about 78% nitrogen gas .
• All living organisms (plants and animals)  need nitrogen for proteins, chlorophylls, and nucleic acids.
• Plants cannot use atmospheric nitrogen directly.
• Nitrogen Fixation:
  • Some bacteria (such as Rhizobium that live in the roots of pulses) and blue-green algae convert atmospheric nitrogen into usable nitrogen compounds.
  • Lightning also leads to the fixation of atmospheric nitrogen.

Nitrogen Cycle:

• Absorption by plants of nitrogen compounds in the soil.
• Eating of plants by animals.
• Decomposition of dead plants and animals by microorganisms, causing nitrogen compounds to move back into the soil.
• Some bacteria convert soil nitrogen compounds into nitrogen gas, which goes back into the atmosphere.
• This cycle goes on continuously, which maintains the balance of nitrogen in the atmosphere.