Lesson 2: Observing Bacterial Growth

Key Idea

The world is full of diverse life forms, many of which are microscopic. One common example is bacteria. A single bacterium is a complete living organism, but it is so tiny that it is invisible to the naked eye.

This means that even when bacteria are present on a surface or in a liquid, we cannot see them as individuals. We require scientific tools to verify their presence because our eyes cannot resolve objects at such a small scale.

Key Idea

Although a single bacterium is invisible, it has the ability to reproduce. Over time, a single cell divides repeatedly, creating copies of itself. This rapid multiplication can generate millions of individual bacteria from just one starting cell in a matter of days.

When these millions of bacteria are grouped together in one place, they form a visible spot called a colony. Observing a colony on a culture plate provides visual evidence that invisible cells are present and reproducing, effectively bridging the gap between the microscopic and macroscopic worlds.

Key Idea

The rule that all living things are made of cells applies to every organism, regardless of its size. Just as a whale is made of trillions of cells, a bacterium is also made of cells.

In the case of bacteria, the entire organism consists of just one single cell. Because this fundamental unit of life is microscopic, the organism itself cannot be seen without magnification. This reinforces the concept that the cell is the universal building block of life.