• Structural unit: Cells provide the basic building blocks for all living things. Just like bricks are the building blocks of a house, cells are the building blocks of tissues, organs, and organ systems.
• Functional unit: Cells carry out all the necessary processes for life. They can take in nutrients, convert these nutrients into energy, and perform specialized functions.

Cells are highly organized and contain a variety of structures called organelles, which perform specific functions. All cells are surrounded by a membrane, which regulates the passage of substances in and out of the cell.

There are two main types of cells:

• Prokaryotic cells: These cells do not have a nucleus or other membrane-bound organelles. Bacteria and Archaea are examples of organisms with prokaryotic cells.
• Eukaryotic cells: These cells have a nucleus and other membrane-bound organelles. Plants, animals, fungi, and protists are examples of organisms with eukaryotic cells.

For more information, you can refer to these resources:

• Cells: The Fundamental Units of Life - NCBI Bookshelf
• Cell Biology - Nature Scitable