The Cell

3 04 2015

Cells are the smallest unit of life that can replicate independently, and are often called the “building blocks of life”. The study of cells is called cell biology.

The Cell theory holds true for all organisms , whether they be unicellular or multicellular:

  • All living things are composed of cells.
  • The cell is the basic functional unit of life.
  • Cells arise only from pre-existing cells.
  • Cells carry genetic information in the form of DNA. This genetic material is passed on form parent to daughter cell.

One of the primary obstacles that prevented early scientists from being able to study cells was their size.  Today , our primary techniques for examining the organism at the organ, tissue, cellular or subcellular levels are  microscopy, autoradiography, and centrifugation.

Prokaryotes versus Eukaryotes 

The first major biological distinction we can make between living organisms is whether they are prokaryotes or eukaryotes. The prokaryotic/eukaryotic distinction comes from the lack ore presence of a nucleus, respectively. Karyon is Greek for “kernel” or “nucleus”. Pro means “before”, and eu-means “true”. Thus, prokaryotes existed before nuclei, and eukaryotes have true nucley.


Prokaryotes are the simplest of all organisms. They include all bacteria as well as blue green-algae. Their outer cell wall does not enclose any membrane -bound organelles( such as nuclei or endoplasmic reticilum). The gentic material of the organism is contained in a single circular molecule of DNA concentrated in an area of the cell called the nucleoid region.

Read the rest of this entry »