Microorganisms Useful and Harmful
NCERT Class 8 • Science • Chapter "Microorganisms Friend and Foe"
Microorganisms Useful and Harmful
Microorganisms are organisms too small to be seen with the naked eye. They live everywhere, from soil and water to inside our own bodies, and while a small number cause disease, the majority are useful and some are absolutely essential to life.
Types and Useful Roles
- The main groups are bacteria, fungi, protozoa, algae and the virus, which is on the borderline of living and non living.
- A virus can reproduce only inside a host cell, which is why it is considered non living outside one.
- In food, lactobacillus turns milk into curd and yeast ferments dough for bread and produces alcohol.
- In medicine, microbes produce antibiotics such as penicillin and are used to make vaccines.
- In agriculture, rhizobium in the root nodules of leguminous plants fixes atmospheric nitrogen and enriches the soil.
- Blue green algae also fix nitrogen and are used as biofertiliser in paddy fields.
- In cleaning, microbes decompose dead plants and animals and organic waste into simple substances, returning nutrients to the soil.
- Microbes are also used in sewage treatment and in producing biogas from animal dung and farm waste.
- Some microbes also spoil leather, wood and textiles, so protective treatment is applied to these materials.
Harmful Effects and Food Preservation
- Pathogenic microbes cause disease in humans, animals and plants.
- Microbes also cause food poisoning by spoiling food and releasing toxic substances.
- Food preservation works by removing the conditions that microbes need: water, warmth and nutrients.
- Salting and sugaring draw water out of microbial cells; drying removes water from the food.
- Oil and vinegar in pickles create a medium in which microbes cannot survive.
- Heat methods include boiling and pasteurisation, in which milk is heated and cooled quickly.
- Cold methods, refrigeration and freezing, slow microbial growth, and chemical preservatives and airtight sealing complete the list.
| Microbe | Useful Role |
|---|---|
| Lactobacillus | Turns milk into curd |
| Yeast | Ferments dough and makes alcohol |
| Rhizobium | Fixes nitrogen in root nodules |
| Blue green algae | Biofertiliser in paddy fields |
Pasteurisation — the process of heating milk and cooling it suddenly to kill harmful microbes without changing its taste.
Exam me kaise aata hai
- Which microbe turns milk into curd — lactobacillus
- Which microbe fixes nitrogen in root nodules — rhizobium
- Heating milk and cooling it suddenly is — pasteurisation
- Yeast is used in bread making because it produces — carbon dioxide
UPSC/State PSC ke liye
- Rhizobium matters agriculturally because it converts atmospheric nitrogen into a form plants can use, which is why legumes are grown in rotation with cereals.
- Preservation methods all attack one of three requirements — water, warmth or nutrients — which is why so many different looking methods work on the same principle.
Yahan confuse hote hain
✗ All microorganisms are harmful | Most are useful or harmless; only some are pathogenic | ✓
✗ A virus can reproduce on its own | A virus reproduces only inside a host cell | ✓
✗ Refrigeration kills microbes | Refrigeration only slows their growth | ✓
Ek nazar me
- Microbes are bacteria, fungi, protozoa, algae and viruses.
- They make curd and bread, produce antibiotics, fix nitrogen and decompose waste.
- Pathogenic microbes cause disease and food poisoning.
- Preservation removes water, warmth or nutrients that microbes need.
Ab practice karein
Health, disease aur microbes se har exam me factual questions bante hain. ExamAtlas ke mock test se abhi practice karein.