A cell is the smallest structural and functional unit of an organism. It is made up of a cell wall, a cell membrane, a nucleus and cytoplasm, among other elements.
The cell wall and membrane offer support and protection to the entire cell. The cell membrane acts as a barrier between the cell and the environment and controls the movements of particles moving in and out of the cell. It also maintains homeostasis.
The nucleus controls all cell activities and houses DNA, which is the cell's hereditary material. Cytoplasm is responsible for protecting all of the cell's organelles. Organelles are structures within cells that perform specialized cellular tasks.
Cells also contain mitochondria. These are complex organelles that convert the energy from food into material that the cell can use. Ribosomes are a part of a cell responsible for producing proteins.
Cells essentially are the building blocks of every living thing. The human body is host to trillions of cells. These cells perform many functions such as extracting nutrients from food and converting it into energy. They are able to replicate themselves due to the hereditary material they contain.
In complex organisms that contain more than one cell, cells specialize into different types that are adapted to perform specific functions. Examples of these cells in mammals include skin cells, blood cells, neurons, muscle cells and stem cells.