What is Endosymbiotic Theory?

About Endosymbiotic Theory

• The endosymbiotic theory states that some of the organelles in today’s eukaryotic cells were once prokaryotic microbes.
• In this theory, the first eukaryotic cell was probably an amoeba-like cell that got nutrients by phagocytosis and contained a nucleus that formed when a piece of the cytoplasmic membrane pinched off around the chromosomes.
• Some of these amoeba-like organisms ingested prokaryotic cells that then survived within the organism and developed a symbiotic relationship.
• Mitochondria formed when bacteria capable of aerobic respiration were ingested; chloroplasts formed when photosynthetic bacteria were ingested. They eventually lost their cell wall and much of their DNA because they were not of benefit within the host cell.
• The endosymbiotic theory describes how a large host cell and ingested bacteria could easily become dependent on one another for survival, resulting in a permanent relationship.
• Over millions of years of evolution, mitochondria and chloroplasts have become more specialized, and today they cannot live outside the cell.

Prokaryotes vs. Eukaryotes

• All living things can be divided into three basic domains: Bacteria, Archaea, and Eukarya.
• The primarily single-celled organisms found in the Bacteria and Archaea domains are known as prokaryotes. These organisms are made of prokaryotic cells—the smallest, simplest, and most ancient cells.
• Organisms in the Eukarya domain is made of more complex eukaryotic cells. These organisms, called eukaryotes, can be unicellular or multicellular and include animals, plants, fungi, and protists. 
• The biggest distinction between them is that eukaryotic cells have a distinct nucleus containing the cell’s genetic material, while prokaryotic cells don’t have a nucleus and have free-floating genetic material instead. 
• Eukaryotes developed at least 2.7 billion years ago, following 1 to 1.5 billion years of prokaryotic evolution.
• Eukaryotic cells have several other membrane-bound organelles not found in prokaryotic cells. These include the mitochondria, rough and smooth endoplasmic reticulum, golgi complex, and in the case of plant cells, chloroplasts (conduct photosynthesis).
• Although prokaryotic and eukaryotic cells have many differences, they share some common features, including the following:
  • DNA.
  • Cell (or plasma) membrane
  • Cytoplasm: Jelly-like fluid within a cell that is composed primarily of water, salts, and proteins.
  • Ribosomes: Organelles that make proteins.

Q1: What is Phagocytosis?

Phagocytosis, or “cell eating”, is the process by which a cell engulfs a particle and digests it. The word phagocytosis comes from the Greek phago-, meaning “devouring”, and -cyte, meaning “cell”. Cells in the immune systems of organisms use phagocytosis to devour bodily intruders such as bacteria, and they also engulf and get rid of cell debris. Some single-celled organisms like amoebas use phagocytosis in order to eat and acquire nutrients.

Source: Can the newly discovered organelle help engineer plants to fix nitrogen?

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