1. Basic Unit of Life: Cells are the fundamental building blocks of all living organisms. Whether a single-celled organism like bacteria or a complex multicellular organism like a human, all life is made up of cells.

2. Self-Contained Units: Cells are enclosed by a membrane that separates their internal environment from the outside world. This membrane controls what enters and exits the cell, allowing it to maintain its own unique internal conditions necessary for life.

3. Carry Out Life Processes: Cells are capable of performing all the essential functions of life, including metabolism, growth, reproduction, and response to stimuli. They contain structures like DNA, ribosomes, and mitochondria that carry out these vital processes.