Cell Theory

Cell theory refers to the idea that the new cells are formed from other existing cells and that the cells are the fundamental unit of structure, function and organization in all living organisms. Cells manage a wide range of functions: growing, moving, reproducing, and so on; and most of those functions require energy. There are two types of cells: the simplest cells such as bacteria are known as Prokaryotic cells, and human cells are known as Eukaryotic cells. The main difference between each of these cells is that a Eukaryotic cell has a nucleus and a membrane bound section in which the cell holds the main DNA which are building blocks of life. Eukaryotic cells are much larger than prokaryotic cells – typically with a diameter of around 10-100m, compared to a prokaryote’s 0.2-2m. Cells have many structures inside of them called organelles. These organelles are like organs in human body, they have specific functions and help the cells stay alive. For example, cells have plasma membrane which is a thin semipermeable membrane that surrounds the cytoplasm of a cell. It is called “semipermeable” because it allows just some material to pass through while keeping other substances out. Its function is to protect the integrity of the interior of the cell. In addition, the nucleus is found in every Eukaryotes. It is the largest organelle of the cell. There are two major functions of the nucleus: it stores the cell’s hereditary material (DNA), and it’s responsible for the cell’s activities such as growth, intermediary metabolism, protein synthesis, and reproduction. According what I know about cells, I agree with the idea that viruses are not considered living. Viruses lack of key characteristics of living organism. Viruses do not have cells. They are just fractions of DNA (or RNA). Although there is a protein coat that protects their genetic material (either DNA or RNA), they do not have a cell membrane or other organelles. As I mentioned previously, living things use energy to maintain their functions. In contrast, outside of a host cell, viruses do not use any energy. They only become active when they come into contact with a host cell. Once activated, they use the host cell’s energy and tools to make more viruses. Scientist all over are debating whether or not a virus is in fact a living organism. There are many different opinions about this touchy topic from many different scientists. Just because a virus share some characteristics of living organism, it does not mean that it is alive.  [pic 1][pic 2]