The Parts of a Cell

Image derived from one on Wikipedia

The living cell is an amazing structure! All living things are made up of cells, the smallest units of life. (For this reason--and because they cannot reproduce without a host--viruses, smaller than cells, are not properly considered "alive.") Plant and animal cells exhibit some differences (most notably, plant cells have a rigid cell wall, and their chloroplasts can convert light energy into chemical energy through photosynthesis). But let's look at the very basic parts of an animal cell, moving generally from the outside to the inside. (There are many more details, but these are the main things.)

• the cell membrane: a layer of plasma that works like a "skin" to surround and contain the contents of the cell. In plant cells, the cell wall would be outside of this. The cell membrane has mechanisms that allow things like oxygen, water, and nutrients to enter the cell, and waste products and carbon dioxide to leave it, but larger molecules are strictly controlled. Thus, the cell membrane referred to as semipermeable.
• cytoplasm: the "stuff" in the cell; the substance within which the cell's other components are contained.
• ribosomes: These tiny organelles (meaning "small organs") contain the cell's ribosomal RNA (rRNA). They serve to produce protein within the cell.
• mitochondria (singular mitochondrion): the cell's "power plant," which helps in producing energy within the cell
• the nucleus: This important organelle contains the cell's DNA, and serves as a sort of "control center" for the cell's activities (such as growth, protein synthesis, and reproduction/division).
• the nucleolus: located inside the nucleus, its main function is to assist in the production of ribosomes