An introduction to cells

AN INTRODUCTION TO CELLS

Cells are the basic units of life . Although the chickeneggs that people eat for breakfast are an example oflarge, macroscopic cells visible tothe naked eye, most cells are microscopic, meaning that a person cannot see them with their unaided eye . Instead, to view these microscopic cells, it is necessary to use a microscope .

Some organisms, including bacteria andyeast, are unicellular, meaningthey are made up of only one cell . Other organisms, such as mushrooms, plants, dogs, andhumans, are multicellular, meaning they aremade up of numerous cells . Although humans are quite different from bacteria or plants, and the differences are obvious, there arealso similarities among the cellsmaking up these organisms. For example, all cells have a plasma membrane and have gel-like cytoplasminside . All cells contain and use genetic material known as DNA . There are also other similarities .

Figures 1-1,1-2, and 1-3 showthe structure  ofanimal, plant, and bacterial cells, respectively . Prokaryotic (prokaryote) organismsinclude bacteria and archaea . Prokaryotic organisms do not containmembrane-bound organelles, such as the nucleus or Golgi apparatus, and they are unicellular . Eukaryotic (eukaryote) cells make up organisms such as animals and plants and do contain membrane-

bound organelles . Most eukaryotic organisms are multicellularalthough there are a few unicellular eukaryotic organisms, such as yeast.