🌐 Real-World Connection: Imagine leaving a piece of bread out for three days. Tiny green and white spots appear on it — mould! You never saw anything land on it, yet something invisible transformed your food. The world is full of living things so incredibly small that millions of them can fit on the tip of a needle. Some make your curd thick and your bread fluffy; others cause diseases. This chapter uncovers the invisible living world hiding all around you.
🔬 Topic 1: Microorganisms – Tiny Living Things
Microorganisms are very tiny living things.
We cannot see them with our eyes.
We need a microscope to see them.
They live in water, air and soil.
Some are helpful, some are harmful.
🦠 Topic 2: Bacteria – Single Cell Organisms
Bacteria have only one tiny cell.
They are found everywhere around us.
Some bacteria help us make curd.
Some bacteria make us sick.
They are very, very small in size.
🧫 Topic 3: Viruses – Not Fully Alive
Viruses are even smaller than bacteria.
They are not fully alive on their own.
They need a host body to grow.
They cause cold, flu and COVID.
They can spread from person to person.
🍄 Topic 4: Fungi – Mushrooms and Moulds
Fungi grow on dead or old things.
Mushrooms and bread mould are fungi.
They like warm and wet places.
Some fungi we can eat safely.
Yeast is a fungus used in bread.
🌿 Topic 5: Algae and Protozoa
Algae are plant-like tiny living things.
They make their own food using sunlight.
Green pond water has algae in it.
Protozoa are animal-like tiny living things.
Amoeba is a well-known protozoa.
😊 Topic 6: Friendly Microorganisms
Lactobacillus bacteria help us make curd.
Yeast helps bread become soft and fluffy.
Antibiotics are medicines made from fungi.
Bacteria help make the soil rich.
They help in making cheese and vinegar.
⚠️ Topic 7: Harmful Microorganisms
Some microorganisms cause diseases in us.
Bacteria can cause typhoid and TB.
Viruses cause cold and chicken pox.
Fungi cause ringworm skin infections.
Protozoa cause malaria and dysentery.
🥫 Topic 8: Food Preservation Methods
We preserve food to stop it from spoiling.
Salt and sugar keep food safe longer.
Oil and vinegar also help preserve food.
Keeping food in a fridge slows germs.
Heating and drying food kills germs too.
🌱 Topic 9: Nitrogen Fixation by Bacteria
Plants need nitrogen to grow well.
Air has nitrogen but plants cannot use it.
Rhizobium bacteria live in plant roots.
They change air nitrogen into usable form.
This process is called nitrogen fixation.
💉 Topic 10: Vaccination and Louis Pasteur
A vaccine protects us from diseases.
It has weak or dead germs inside it.
Our body learns to fight those germs.
Louis Pasteur made the first vaccine for rabies.
Edward Jenner made the smallpox vaccine.
Picture Diagrams – See and Learn
Diagram 1: The four main types of microorganisms
Diagram 2: A bacteria cell has simple parts
Diagram 3: Some microorganisms help us, some harm us
Diagram 4: Six ways to preserve food (click Play!)
Diagram 5: Vaccines teach our body to fight germs
Solved Examples – Step by Step
Example 1: Why does milk become curd?
1
Milk is kept in a warm place.
2
Lactobacillus bacteria are added to milk.
3
Bacteria eat the milk sugar (lactose).
4
They turn milk into thick, sour curd.
Answer: Lactobacillus bacteria change milk into curd.
Example 2: How does bread become soft?
1
We add yeast to the bread dough.
2
Yeast eats the sugar in the dough.
3
It makes carbon dioxide gas (CO2).
4
The gas makes the dough rise and grow.
Answer: Yeast makes gas that puffs up bread.
Example 3: How does nitrogen fixation work?
1
Air has nitrogen gas all around us.
2
Plants cannot use nitrogen from the air.
3
Rhizobium bacteria live in plant roots.
4
They change nitrogen into a usable form.
Answer: Rhizobium bacteria fix nitrogen for plants.