AP BIOLOGY

Detailed explanation-1: -What is the endosymbiotic theory? One theory that may explain how eukaryotes became so complex is the endosymbiotic theory. This theory proposes that organelles like mitochondria and chloroplasts were once free-living prokaryotic cells that began to live within a larger host cell.

Detailed explanation-2: -While endosymbiosis is widespread among eukaryotes and between eukaryotes and prokaryotes [25, 26], endosymbiosis among prokaryotes is rare [25, 27, 28]. In contrast, there seems to be a diversity of obligate ectosymbiotic organisms belonging to both archaea and bacteria that depend on a prokaryotic partner [29-32].

Detailed explanation-3: -The Theory Endosymbiotic Theory proposes that mitochondria developed from proteobacteria, or Rickettsia, (respiring Bacteria) and that chloroplasts were originally from cyanobacteria. Anaerobic bacteria engulfed the aerobic bacteria, which was not completely digested.

Detailed explanation-4: -The endosymbiotic theory states that some of the organelles in eukaryotic cells were once prokaryotic microbes. Mitochondria and chloroplasts are the same size as prokaryotic cells and divide by binary fission. Mitochondria and chloroplasts have their own DNA which is circular, not linear.

Detailed explanation-5: -The mitochondrion and the chloroplast are both organelles that were once free-living cells. They were prokaryotes that ended up inside of other cells (host cells). They may have joined the other cell by being eaten (a process called phagocytosis), or perhaps they were parasites of that host cell.