CHAPTER 2 MICROORGANISMS
Living organisms that we cannot see with our eyes alone are called microorganisms or microbes. They are classified into four major groups: bacteria, fungi, protozoa and some algae.
Viruses are also microorganisms but they reproduce only inside the host organism.
Disease causing microorganisms are called pathogens. Some common diseases caused by microorganisms are:
Chicken Pox: Virus
Hepatitis B: Virus
PRESERVATION OF FOOD
(i) Chemical method: By using preservatives
(ii) By common salt
(iii) By sugar
(iv) In oil and vinegar
(v) Heat and cold treatment: Pasteurization
(vi) Storage and packing
Certain bacteria present in the soil take nitrogen from the air and convert it into nitrogenous compounds. Certain bacteria convert nitrogenous compounds present in the soil into nitrogen gas which is then released into the atmosphere.