Questions: Single-Celled Organisms

Question 1

What makes a single-celled organism different from a multi-celled organism?

• A. It cannot reproduce
• B. It is made of only one cell that does everything
• C. It does not need energy
• D. It is always harmful

Answer: (B)

A single-celled organism consists of one cell that carries out all life functions — nutrition, energy production, waste removal, and reproduction. Multi-celled organisms have many cells that specialize in different tasks. Single-celled organisms can reproduce, do need energy, and are usually harmless.

Question 2

Most bacteria cause disease.

• T. True
• F. False

Answer: False

Only a small fraction of bacteria cause disease. Many bacteria are essential for life — they help decompose dead matter, recycle nutrients in soil, and aid in human digestion. Some bacteria are even used to make foods like yogurt and cheese.

Question 3

Explain how a single-celled organism like an amoeba can survive without specialized organs.

Model answer: An amoeba's single cell performs all necessary life functions on its own. It takes in food by surrounding particles with its cell membrane, breaks down food for energy, removes waste, and reproduces by splitting in two. It does not need separate organs because one cell handles everything.

This highlights the self-sufficiency of cells. Organs are collections of specialized cells in multi-celled organisms, but a single cell already contains all the molecular machinery needed for life. Specialization is a strategy for efficiency in larger organisms, not a requirement for life itself.