One of the following is the unit of life

1. Analyze the question The question asks for the "unit of life", meaning the smallest structural and functional unit that can carry out all the activities of a living thing.

2. Explain the concept Living things are organized in levels, from simple to complex:

Cell → Tissue → Organ → System → Organism

• Cell: the smallest unit that shows all the characteristics of life (respiration, growth, reproduction, excretion, response to stimuli, and so on).
• Tissue: a group of similar cells doing the same job (e.g. muscle tissue).
• Organ: different tissues working together (e.g. the heart, the stomach).
• System: several organs working together (e.g. the digestive system).

The cell theory also states that all living things are made of cells, and that the cell is the basic structural and functional unit of life. Some organisms, like Amoeba and Paramecium, are made of just one cell and still carry out every life process. This shows that a single cell is enough to be "alive".

3. Solution

• B (tissues): made of many cells, so it is not the smallest unit.
• C (organ): made of many tissues, so it is even bigger.
• D (system): made of many organs, so it is bigger still.
• A (cell): the smallest unit that can live independently and carry out all life functions.

4. Answer A. cell

5. Tip Remember the order "Can The Old Sage Open?" for Cell, Tissue, Organ, System, Organism. Whenever you see "unit of life", "basic unit", or "building block", think cell, the first in the chain.