October 17, 2012
What is a Cell?
Hi I’m Emerald Robinson. In this “What Is” video we explore cells. Cells are the smallest structural and functional units of all living organisms.
All cells have a cell membrane, which controls the flow of substances in and out of the cell; ribosomes, which makes protein – necessary for all cell functions; DNA, the genetic instructions the cell needs to make protein; and cytoplasm, the watery substance that contains all the cell’s structures.
Some cells, like bacteria, are individual, self-replicating, independent life forms called unicellular organisms or single-celled organisms. Other cells are part of multicellular organisms, such as us humans, and collectively carry out specialized functions to keep that organism alive.
The many different kinds of cells that exist can be divided into two main categories, prokaryotes and eukaryotes. Prokaryote cells lack a nucleus. Bacteria are the best-known and most studied form of prokaryotic organisms. A recently discovered second group of prokaryotes, called archaea, also exists.
Cells that do have nuclei are classified as eukaryotes. This includes fungus, plant, and animal cells, as well as some unicellular organisms. Besides a nucleus, the other significant difference between prokaryotes and eukaryotes is that eukaryotic cells contain specialized structures called organelles, in which specific life sustaining activities take place for the cell.
The major organelles that exist include: the golgi apparatus, which sort, package, process, and modify proteins; mitochondria, which are the energy provider for cells; vacuoles, the storage units found in some cells; the nucleus, which controls all activities in the cell; and the endoplasmic reticulum, which serves many general functions. Plant cells also have chloroplasts, which are responsible for photosynthesis of sunlight.
Most cells are too small to be seen without the aid of a microscope, there are however exceptions, for example the nerve cell of a giant squid can be 39 feet long!