Unicellular organisms

Unicellular organisms are living things made of just one cell, and that single cell carries out all the life processes needed to survive.

• One cell does everything: it takes in food, releases energy, removes wastes, responds to its surroundings, and reproduces.
• They are usually microscopic, so you often need a microscope to see them clearly (for example, many bacteria).
• Examples include bacteria, Amoeba, and yeast.
• Because there is only one cell, there is no division of labour like in our body—there are no separate tissues or organs; the same cell handles all jobs.
• A helpful way to imagine it: a unicellular organism is like a one-person shop where the same person is the manager, worker, cleaner, and cashier—all at once.

Even though they are tiny, unicellular organisms are extremely important in nature and daily life—many help in decomposition, fermentation, and keeping ecosystems running smoothly.