Every living thing is built from cells, and every cell is run by tiny organelles, each with its own job. Microorganisms are too small to see, but they shape our food, our health and our diseases.
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A cell is like a tiny factory — each organelle has one job, and the cell only works when all of them do their job together.
📌 What each organelle does
Nucleus: the control centre — holds the DNA and directs every activity of the cell.
Mitochondria: the "powerhouse" — releases energy from food through respiration.
Chloroplasts (plants only): capture sunlight to make food through photosynthesis.
📊 Plant cell vs animal cell
| Feature | Plant cell | Animal cell |
|---|---|---|
| Cell wall | Present (made of cellulose) | Absent |
| Chloroplasts | Present | Absent |
| Vacuole | One large, permanent vacuole | Small, temporary vacuoles (if any) |
| Shape | Usually fixed, rectangular | Usually round or irregular |
Not all microbes are germs. Many microorganisms are essential to our food, our farms and even our own digestion.
📊 Microbes at work
| Microbe | Used for | Process |
|---|---|---|
| Yeast (fungus) | Bread, idli/dosa batter | Fermentation — releases CO₂ that makes dough rise |
| Lactobacillus (bacteria) | Curd from milk | Converts milk sugar (lactose) into lactic acid |
| Rhizobium (bacteria) | Soil fertility in legume crops | Fixes atmospheric nitrogen into the soil |
| Penicillium (fungus) | The antibiotic penicillin | Produces a substance that kills certain bacteria |
Disease vectors: a vector does not itself cause disease — it CARRIES the microbe that does. The female Anopheles mosquito is the vector for malaria (caused by the Plasmodium parasite, not the mosquito itself).
Achievers questions often ask you to connect an organelle's structure to what happens if it is missing or damaged.
✨ Cause and effect
No mitochondria
no energy release
The cell could not carry out any energy-demanding activity.
No cell wall (in a plant cell)
no rigid shape
The cell would lose its fixed shape and could easily burst.
Pro tip: Vaccines work by preparing the body's immune system to recognise a specific pathogen in advance, so it can respond faster the next time — this is different from an antibiotic, which directly kills bacteria after an infection has started.
12 NSO-pattern questions on cell structure and microorganisms, including two Achievers-level questions.
