Beyond Our Naked Eye

Overview

Many living things are too small to be seen with the naked eye. These microorganisms include bacteria, fungi, protozoa, algae, and viruses. They live everywhere and can be both useful and harmful to humans.

Key concepts

• Microorganisms are seen only with a microscope.
• Main groups: bacteria, fungi, protozoa, algae, and viruses.
• Useful microbes make curd, bread, and antibiotics, and increase soil fertility.
• Harmful microbes cause diseases and spoil food.
• Fermentation by yeast produces carbon dioxide and alcohol.

Important terms / formulae

• Pathogen: a disease-causing microorganism.
• Antibiotic: a medicine that kills or stops bacteria.
• Nitrogen fixation: bacteria converting atmospheric nitrogen into usable form.
• Preservation: methods to stop food spoilage by microbes.

Solved example or key process

To make curd: warm milk is kept and a little curd (containing Lactobacillus bacteria) is added. The bacteria multiply and convert milk sugar into acid, which thickens the milk into curd. This shows a useful role of microorganisms.

Important questions

1. Name the major groups of microorganisms.
2. State two useful and two harmful effects of microbes.
3. How does yeast help in making bread?
4. List three methods of food preservation.

Quick revision

Microorganisms are tiny invisible living things. They help in making curd, bread, medicines, and enriching soil, but some cause diseases and spoil food. Good hygiene and preservation protect us from harmful microbes.