Welcome to the Invisible World!

Did you know that right now, there are millions of tiny living things all around you? They are on your desk, in the air, and even on your skin! We call these microorganisms. They are so small that we cannot see them with our eyes alone—we usually need a microscope to see them.

In this chapter, we will meet these "invisible neighbors" and learn how they help us and how they can sometimes make us sick. Don't worry if it sounds a bit "creepy" at first; most of them are actually very helpful!

1. The Three Main Types of Microorganisms

In our Science curriculum, we focus on three main groups of microorganisms. You can think of them as three different families:

A. Bacteria (細菌)

Bacteria are very simple, single-celled living things. They are shaped like tiny rods, balls, or spirals. They are found everywhere on Earth!

Example: Some bacteria live in your stomach and actually help you digest your food!

B. Fungi (真菌)

You might have seen big fungi like mushrooms in a forest, but many are microscopic. Yeast (used to bake bread) and mold (the fuzzy green stuff that grows on old bread) are types of fungi.

Example: If you leave an orange out too long, the blue-green fuzz you see is a colony of microscopic fungi.

C. Viruses (病毒)

Viruses are the smallest of all microorganisms. They are so tiny that they cannot even grow or reproduce on their own. They must enter the body of another living thing (like a human, animal, or plant) to make copies of themselves.

Example: The "flu" (influenza) is caused by a virus.

Key Takeaway: The three main types you need to know are Bacteria, Fungi, and Viruses.

2. Are Microorganisms Friends or Foes?

It is a common mistake to think that all microorganisms are "germs" that cause disease. In reality, they have many different roles.

How Microorganisms Help Us (Benefits)

  • Making Food: We use bacteria to turn milk into yummy yogurt and cheese. We use yeast (a fungus) to make bread rise and become fluffy.
  • Nature's Recyclers: When a leaf falls or an animal dies, fungi and bacteria break them down. This turns them into nutrients that go back into the soil to help new plants grow.
  • Producing Oxygen: Some microorganisms in the ocean produce a large part of the oxygen we breathe!
  • Medicine: We actually use some microorganisms to create medicines that fight off other "bad" microorganisms.

How Microorganisms Hurt Us (Harms)

  • Causing Diseases: Some microorganisms are "pathogens." They can cause illnesses like food poisoning (bacteria), the flu (virus), or athlete's foot (fungi).
  • Spoiling Food: Bacteria and mold can make our food rot, smell bad, and become unsafe to eat.

Did you know? There are more bacteria in your mouth right now than there are people on the entire Earth! But don't panic—most of them are harmless or even helpful for keeping your mouth healthy.

3. Antibiotics: Our Tiny Shields

When we get a sickness caused by bacteria, a doctor might give us a special medicine called antibiotics.

What do Antibiotics do?

Antibiotics are chemicals that can kill bacteria or stop them from growing. They are like "super-soldiers" that target bacterial invaders.

The Golden Rule of Antibiotics

Important: Antibiotics only work against bacteria. They do not work against viruses. This is why a doctor won't give you antibiotics for a common cold or the flu, because those are caused by viruses!

The Danger of Misuse (Antibiotic Resistance)

If we use antibiotics the wrong way, it can be dangerous. This is called misuse. Examples of misuse include:

  • Taking antibiotics when you have a virus (like a cold).
  • Stopping your medicine early because you "feel better" before the doctor told you to stop.

What happens if we misuse them?
The bacteria can learn how to "fight back" and become resistant. This means the medicine will no longer work against them. These "super-bacteria" are much harder to treat and can be very dangerous for everyone.

Key Takeaway: Always follow your doctor's instructions! Finish the whole course of medicine to make sure all the bad bacteria are gone.

Quick Review Summary

1. Types: Bacteria (simple cells), Fungi (yeast/mold), Viruses (the smallest).

2. Benefits: They help make food (yogurt/bread), recycle nutrients in nature, and make medicines.

3. Harms: They can cause disease and spoil our food.

4. Antibiotics: They kill bacteria only. Misusing them leads to antibiotic resistance, which makes diseases harder to cure.

Note: To learn more about how these microorganisms spread from person to person, you can look at the chapter on "Infectious and Non-infectious Diseases." To see how to look at them closely, check out "Cells and the Microscope!"