Grade 4 (age 9-10)

Microorganisms & Our Life

Microorganisms are living things so tiny we need a microscope to see them. Bacteria, molds, and protists are all microbes, and they live almost everywhere. Some help us by making foods like yogurt and kimchi, while others can spoil food. Switch the microscope view to see how different microbes look.

What is a microorganism?

🔬 Tiny invisible life

①Microbes are too small to see with the naked eye

②You need a microscope to see them

③They live everywhere — soil, water, air, our bodies

④Bacteria, fungi, and protists are microbes

Types of Microorganisms

Microbe Types

Classification of Microbes

Helpful and Harmful Microbes

🥛 Helpful Microbes

①Lactobacilli: make yogurt and kimchi (fermentation)

②Yeast: makes bread rise

③Molds: make miso, soy sauce, cheese

④Antibiotics: discovered from blue mold

⚠️ Microbes to Watch Out For

①Food-poisoning bacteria: grow on spoiled food

②Mold: spoils food

③Cold viruses: cause colds

④Hand washing reduces harmful microbes!

Summary

Types of Microbes

Bacteria / Fungi / Protists

Invisible but everywhere

Fermented Foods

Microbes + ingredients = fermented foods (kimchi, yogurt, miso)

Helpful microbes create delicious foods

🎯 Key Points

①Microbes are tiny invisible organisms

②Three types: bacteria, fungi, protists

③Helpful: make fermented foods (kimchi, yogurt)

④Harmful: spoil food and cause disease

⑤Hand washing and food care prevent harmful microbes

Examples and Unit Test

Example 1

Why can microorganisms not be seen with the naked eye, and how do we observe them?

Microorganisms are very small living things, so they cannot be seen with the naked eye.

That is why we need to magnify them with a microscope to see them.

▸ Because they are too small / observe them with a microscope

Microorganisms are tiny and are observed with a microscope.

Example 2

Which microbe helps make kimchi and yogurt, and what is that process called?

Lactic acid bacteria are microbes that are helpful to us.

Lactic acid bacteria ferment food ingredients to make kimchi and yogurt.

▸ Lactic acid bacteria / fermentation

Helpful microbes make foods like kimchi and yogurt through fermentation.

Unit-test style

Which statement about microorganisms is correct?

①All microorganisms are harmful to people

②Lactic acid bacteria make helpful foods through fermentation

③Microorganisms are easy to see with the naked eye

④Fungi are not microorganisms

⑤Microorganisms live only in soil

▸ ② Lactic acid bacteria make helpful foods through fermentation

Lactic acid bacteria are microbes that ferment food ingredients to make helpful foods like kimchi and yogurt.

Some microbes are helpful (①), they are too small to see without a microscope (③), fungi are microbes too (④), and they live everywhere: soil, water, air, and our bodies (⑤).

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