The development of the endomembrane system was a major step in eukaryotic evolution. The exchange of material between these compartments and between the inside and outside of the cell is essential to maintain cellular integrity. The endomembrane system consists of the nuclear envelope, rough and smooth endoplasmic reticulum (ER), the Golgi apparatus as well as the cell's plasma membrane, and includes the vesicles that bud off these membranes for intracellular transport, exocytosis (stuff leaving the cell) and endocytosis (stuff coming into the cell). Some cellular organelles work together to transport materials into, out of, and within the cell. This is the eukaryotic cell's endomembrane system, a manufacturing and material transport network that enables the cell to make, move and break down cellular products.
The endomembrane system is formed by free ribosomes
A common group of bacteria found in acid bogs and sewage treatment plants has provided scientists with evidence of a 'missing link' in one of the most important steps in the evolution of life on Earth -- the emergence of cells with a nucleus containing DNA (eukaryotic cells).
For billions of years, bacteria (single celled organisms without a nucleus) were the only cellular life form on Earth. Then, about 1.6 to 2.1 billion years ago, eukaryotic cells emerged. These cells (with a nucleus) heralded the evolution of multi-cellular life on Earth including: plants, insects, animals and humans.
Until now scientists have been unable to identify an 'ancestral cell' linking the early prokaryotes with the later eukaryotes, so fusion theory -- where two cells merge to form a new cell -- is often put forward to explain the appearance of these new cell types.
"Our analysis shows that PVC
bacteria, members of which are commonly found in today's sewage treatment plants or acid bogs, represent an intermediate type of cell structure. They are slightly bigger than other known bacteria, and they also divide more slowly." "The structure of PVC suggests that it is an ancestor of a 'missing link' cell which connected prokaryotic to eukaryotic cells along an evolutionary path all those billions of years ago,"
Sewage Water Bacteria: 'Missing Link' in Early Evolution of Life on Earth?