Microorganisms: Friend and Foe
Microorganisms: Friend and Foe
Microorganisms give 2 questions in the Part-III science paper. The examiner tests the four groups, the useful applications and the disease-carrier pairings. The useful half is asked just as often as the harmful one, so both sides of this chapter have to be prepared.
The Four Groups
| Group | Examples | Note |
|---|---|---|
| Bacteria | Lactobacillus, Rhizobium | Prokaryotic, no true nucleus |
| Fungi | Yeast, bread mould, mushroom | Saprophytic mostly |
| Protozoa | Amoeba, Plasmodium, Paramecium | Single-celled animals |
| Algae | Chlamydomonas, Spirogyra | Photosynthetic |
| Virus | Not a cell | Reproduces only inside a host |
A virus is the odd entry: it is not made of cells and shows no life processes outside a host, which is why it is described as being on the borderline of living and non-living. That description is asked directly.
Microorganisms are seen only under a microscope; Anton van Leeuwenhoek first observed them, which links back to the cell topic.
Microorganisms as Friends
| Use | Organism involved |
|---|---|
| Curd from milk | Lactobacillus bacteria |
| Bread and cake rising | Yeast, through fermentation |
| Alcohol production | Yeast |
| Antibiotics such as penicillin | Fungi and bacteria |
| Nitrogen fixation in soil | Rhizobium in root nodules |
| Decomposition of waste | Bacteria and fungi |
| Vaccine production | Weakened microbes |
Fermentation is the process by which yeast converts sugar into alcohol and carbon dioxide, and the carbon dioxide is what makes dough rise. Alexander Fleming discovered penicillin, the first antibiotic, from a mould. Edward Jenner developed the smallpox vaccine, and smallpox has since been eradicated worldwide.
✗ Curd is formed by a fungus | ✓ Curd is formed by Lactobacillus, which is a bacterium
Microorganisms as Foes
| Disease | Caused by | Spread by |
|---|---|---|
| Tuberculosis, typhoid, cholera | Bacteria | Air, food and water |
| Common cold, polio, measles, hepatitis | Virus | Air, water, contact |
| Malaria | Protozoan Plasmodium | Female Anopheles mosquito |
| Kala-azar | Protozoan Leishmania | Sandfly |
| Dengue | Virus | Aedes aegypti mosquito |
| Ringworm | Fungus | Contact |
A carrier is an organism that transmits a disease without causing it. The mosquito is a carrier, not the cause — the parasite is. That distinction is a genuine reasoning question and is frequently set.
Microbes also spoil food. Food preservation works by denying them what they need: salting and sugaring remove water, boiling and pasteurisation kill them, refrigeration slows them, and airtight packing keeps them out. Pasteurisation is named after Louis Pasteur and is asked by name.
Antibiotics and Their Misuse
- Antibiotics act against bacteria and fungi but not against viruses.
- Taking antibiotics for a viral cold is therefore useless and harmful.
- A course must be completed, or resistant bacteria survive.
- Overuse in animals and agriculture also breeds resistance.
The antibiotics do not work on viruses point is the most valuable public-health fact in this topic and is exactly the kind of thing a teacher is expected to convey correctly.
मच्छर रोग का वाहक है, कारण नहीं — कारण परजीवी है।
TRE pointer: Three items repeat here: Lactobacillus for curd, Rhizobium for nitrogen fixation, and the carrier-versus-cause distinction in malaria. For a Bihar paper, the kala-azar and sandfly pairing deserves special attention, since it appears far more often in state papers than in national ones. Antibiotics not working against viruses is the public-health item. With −1/3 negative marking, both tables repay full memorisation.
60-Second Recap
- Bacteria, fungi, protozoa and algae are the four groups; a virus is not a cell.
- Lactobacillus makes curd; yeast ferments sugar to alcohol and carbon dioxide.
- Fleming discovered penicillin; Jenner developed the smallpox vaccine.
- Rhizobium fixes nitrogen in the root nodules of legumes.
- Malaria is caused by Plasmodium and carried by the female Anopheles; kala-azar by a sandfly.
- Antibiotics work on bacteria and fungi, never on viruses.
Frequently Asked Questions
Is a mosquito the cause of malaria?
No, it is the carrier. Malaria is caused by the protozoan parasite Plasmodium, and the female Anopheles mosquito merely transmits it from one person to another. Confusing the carrier with the cause is a genuine reasoning error that examinations test directly.
Do antibiotics work against viral infections?
No. Antibiotics act against bacteria and fungi but have no effect on viruses, so taking them for a common cold is useless and contributes to resistance. Completing a prescribed course matters, because stopping early allows resistant bacteria to survive and multiply.
Which microorganism converts milk into curd?
Lactobacillus, a bacterium. It converts the milk sugar lactose into lactic acid, which sets the milk. Yeast, a fungus, is used in bread and alcohol production through fermentation. The two are set together to check that groups are not being confused.
How does food preservation stop microbial spoilage?
By removing what microbes need. Salting and sugaring draw out water, boiling and pasteurisation kill them, refrigeration slows their growth, and airtight packing keeps them from entering. Pasteurisation is named after Louis Pasteur, who developed the technique.