Living organisms are made up of cells
The first characteristic of a living thing is that, they are made up of cells. A cell is the basic building block of all organisms. It is the smallest unit of organization in a living thing. They contain the organism’s hereditary information (DNA) and can make copies of themselves in a process called mitosis.
Cells are made up of a nucleus and a cytoplasm, enclosed by a thin wall called a membrane, which separates it from its surrounding. Plant cells have a nucleus, cytoplasm and a cell membrane too. The main difference between a plant and an animal cell is that, plant cells have a vacuole, chloroplast and a cell wall.
Here is an illustration of an animal and a plant cell.
Some microorganisms are made up of only one cell, whiles other bigger organisms such as an ant or a lion are made up of millions of different cells.
An organism with only one cell is called a unicellular organism. Unicellular organisms can be complex too, even though they are simply a one-cell organism. They include bacteria, yeast, amoeba and paramecia.
These are organisms that are made up of more than one cell. These organisms have very clear cell structures, with many cell types performing different specialized functions. For example, blood cells only specialize in blood production, and hair cells only specialize in hair growth and repair. The do not mix up. In a multicellular organism, organization of the cells are very important. Here is an illustration of cell organization:
A group of cells can form a tissue—A group of tissues can make up an organ (such as lung) —A set or organs can make up a system (such as a respiratory system)—and the systems can make up the organism.
All the cells that make up the organism have an important role to play for the organism to perform its life functions.