All living things are made up of tiny structures called cells. A living organism can be small as one cell or be made of trillion cells, such as blue whales. A cell is the smallest unit of life and consists of cytoplasm enclosed by a membrane; within the membrane are many biomolecules such as proteins and lipids. There are many types of cells that exist on Earth: for example, the human body has at least 200 different types of cells that perform various functions. The human body has separate cells for blood, eyes, skin, and bones. However, generally we can divide all the cells into two broad categories: prokaryotic and eukaryotic cells.
Prokaryotic cells are simple, single celled organisms that don’t have a nucleus and membrane-bound organelles (organelles are “little organs” and have unique functions that fit into the larger system, i.e. the cell). There is no division of space inside the membrane walls, instead there is one open space. The majority of DNA, or genetic information, is found in the nucleoid, which is located in the center of the cell. The DNA itself is one large loop called a circular chromosome. Prokaryotic cells are typically significantly smaller than eukaryotic cells, as well.
Eukaryotic cells are much more complex than prokaryotic cells as they are able to possess membrane-bound organelles. They also have a membrane-bound nucleus, which differs from the nucleoid in prokaryotic cells. Within the nucleus are multiple linear chromosomes instead of just one circular chromosome. Among the eukaryotic cells there are two types that are most known to us: plant and animal cells. Plant cells are found in plants, and animal cells are found in, you guessed it, animals! Plant cells usually have chloroplast to make food through photosynthesis, vacuoles to hold food and water, and a cell wall that holds the cell’s rectangular cubic shape in place. Animal cells are usually round, have lysosomes to digest substances, don’t have a cell wall, and don’t have large vacuoles.
Regardless of cell type, all cells share several components. The plasma membrane separates the inside of the cell from the outside, and DNA is the genetic material of the cell. Ribosomes synthesize proteins, and the cytoplasm is the area outside the nucleus but inside the plasma membrane.