Which of the following is a living organism?

Step 1: Analyze the question The question asks which option is a living organism, meaning a complete, independent living thing. It is not asking for a part of a living thing.

Step 2: Explain the concept A living organism can carry out all the characteristics of life by itself:

• Nutrition
• Respiration
• Excretion
• Growth
• Reproduction
• Irritability (response to stimuli)
• Movement

Cells, tissues, and organelles are only parts of an organism. They cannot live independently as complete organisms.

Step 3: Examine each option

• A. Muscle: This is a tissue, a part of an animal's body. It is not an organism.
• B. Nucleus: This is an organelle inside a cell that controls cell activities. It cannot live on its own.
• C. Yeast: This is a single-celled fungus. It feeds, respires (it ferments sugar), reproduces by budding, and grows. It is a complete living organism.
• D. Mitochondrion: This is an organelle where aerobic respiration takes place. It is a part of a cell, not an organism.

Step 4: Answer Only yeast is a whole, independent living organism, so the answer is C.

Tip: When you see "living organism" in a question, ask yourself, "Can it survive and reproduce on its own?" Organelles (nucleus, mitochondrion) and tissues (muscle) fail this test. Yeast, bacteria, and amoeba are common single-celled organisms that WAEC likes to ask about.