The cell is the smallest functional unit within a living organism, which can function independently. It is made up of several types of organelles that allow the cell to function and reproduce. There are two general classes of cells that exist: the self-sustaining simple cells known as prokaryotic (bacteria and archaea) and the more complex dependent cells known as eukaryotic. The eukaryotic cells types are generally found in animals, plants, algae, and fungi. For the purpose of this article, the primary focus will be the structure and histology of the animal cell. The major differences between animal and plant cells will be explored as well.

As previously stated, the fundamental components of a cell are its organelles. These organelles are made up of varying combinations of atoms and molecules. The organelles drive different functions of the cell from metabolism, to energy production and subsequently to replication. Cells with particular functions come together to form organs. Organs with interrelated functions work together within a system. These systems, although of different functions, work in synergy to allow the organism to survive. Every aspect of a cell is important for it to survive.

The plasma membrane is the outermost layer of the cell. The main function of the plasma membrane is to protect the cell from its environment. It is often referred to as a fluid mosaic phospholipid bilayer that is hydrophilic externally and internally, but hydrophobic at its core. The hydrophilic property arises from the charged phosphate molecule that forms the head of the phospholipid, and the hydrophobic nature is from the two lipid tails which forms the core. This feature allows the selective permeability of the membrane. For instance, particles that are hydrophilic (e.g. ions) are not able to pass through the hydrophobic core, and those that are hydrophobic (e.g. fats) are repelled from the outer surface. As a result, the cell is able to isolate its internal environment from the external environment. APA