Learning Objectives It is thought that life arose on earth around four billion years ago. 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. Mitochondria and chloroplasts cannot grow outside their host cell. Evidence for this is based on the following:
Although evidence is less convincing, it is also possible that flagella and cilia may have come from spirochetes. Figure \(\PageIndex{1}\): One model for the origin of mitochondria and plastids. This model has an amitochondriate eukaryote engulfing an aerobe and then a cyanobacterium. from KelvinsongExample \(\PageIndex{1}\)
Solutions
SummaryThe endosymbiotic theory states that mitochondria and chlopoplasts in today's eukaryotic cells were once separate prokaryotic microbes. Which is a characteristics of mitochondria and chloroplast that supports the endosymbiotic theory?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.
Why do mitochondria and chloroplasts support the endosymbiosis theory?In addition to the lack of histones, mitochondria and chloroplasts have circular, single stranded DNA. Single stranded, circular DNA is found exclusively in prokaryotes. This evidence supports the endosymbiosis theory because these characteristics would allow the mitochondria and chloroplasts to survive on their own.
Which of the following best supports the endosymbiotic theory?Which piece of evidence best supports the endosymbiotic theory of organelle evolution? The outer membrane of a mitochondrion and chloroplast resemble a eukaryotic cell while the inner membrane resembles that of a bacterial cell.
What are the 3 pieces of evidence that support the endosymbiotic theory?10 Best Evidence of Endosymbiotic Theory. i) Presence of DNA:. ii) Size of Ribosomes:. iii) Inhibition by antibiotics:. iv) Evolutionary relationship:. v) Same size:. vi) Plasma-Membrane:. vii) Enzyme secretion:. viii) Replication and protein synthesis:. |