The History of Cell Theory

The three statements that make up cell theory are that all living things are composed of one or more cells, that cells are the basic units of structure and function in an organism, and that cells come only from the reproduction of pre-existing cells.

The development of the cell theory involved six scientists. First, in 1665, Robert Hooke observed thinly sliced cork and named the tiny compartments he saw "cells". In 1673, Antony van Leewenhoek was the first person to use the microscope to observe living cells. In 1820, Robert Brown was the first person to observe and name the cell nucleus. In 1838, Matthias Schleiden was the first person to state that plants are made up of cells. In 1839, Theodor Schwaan stated those animals are made up of cells. In 1855, Rudolf Virchow stated that cells came from preexisting cells.

Three features that all cells, prokaryotic and eukaryotic, have in common are the plasma membrane, which allows metabolic events and substances and signals to move through, the cytoplasm, which is a semifluid matrix that contains everything between the plasma membrane and DNA region, and ribosomes, which is a structure of protein synthesis.

Prokaryotic cells differ from eukaryotic cells because eukaryotic cells have a nucleus, which prokaryotic cells don't have. An example of a prokaryotic cell is a bacteria, such as paramecium. An example of a eukaryotic cell is an epithelial cell from the cheek or a plant cell.

The cytomembrane system, a series of organelles in which lipids are assembled and new polypeptide chains are assembled and modified into final proteins, contains many different organelles. Ribosomes are non membranous structures that are made up of protein and RNA. They are the site of protein synthesis. The endoplasmic reticulum is continuous with the nuclear envelope and extends through the cytoplasm as a system of membranous tubules and sacs. These form channels that are intracellular highways for movement and transport of substances. Two types of ER exist, smooth and rough. Rough ER has ribosomes. Golgi bodies, or golgi apparatus, are a system of membranous sacs that modify proteins and lipids for export, sort them out, and package them in vesicles for shipment. Vesicles are tiny membranous sacs that move through the cytoplasm or take up positions in it, and store materials. Lysosomes are the garbage collectors of the system. They are vesicles that bud from the Golgi membranes, and contain hydrolytic enzymes that digest organic molecules, old organelles, and microorganisms. Peroxisomes are tiny sacs of enzymes that break down fatty acids and amino acids. In perixosomes, hydrogen peroxide, formed during chemical reactions, is converted back to water and oxygen.

Sources: Biology, 7th Ed. by Campbell