Endosymbiotic theory

Definition

The endosymbiotic theory suggests that eukaryotic cells originated through a symbiotic relationship between different species of prokaryotes. This theory explains how certain organelles, like mitochondria and chloroplasts, were once free-living prokaryotes that became integrated into larger host cells, providing advantages such as energy production and photosynthesis.

5 Must Know Facts For Your Next Test

1. The endosymbiotic theory was popularized by biologist Lynn Margulis in the 1960s, providing evidence that certain organelles originated from prokaryotic ancestors.
2. Mitochondria and chloroplasts have their own circular DNA similar to bacterial DNA, supporting their evolutionary origins as prokaryotic organisms.
3. Both mitochondria and chloroplasts replicate independently of the host cell through a process similar to binary fission, which is characteristic of bacteria.
4. The presence of double membranes around mitochondria and chloroplasts suggests they were engulfed by a host cell, allowing for a symbiotic relationship.
5. The endosymbiotic theory explains the evolutionary transition from prokaryotic to eukaryotic life forms, highlighting the complexity and diversity of cellular life.

Review Questions

• How does the endosymbiotic theory explain the presence of organelles in eukaryotic cells?
  • The endosymbiotic theory explains that organelles like mitochondria and chloroplasts were once independent prokaryotic organisms that entered into a symbiotic relationship with a host cell. This relationship allowed the host cell to gain new capabilities such as enhanced energy production and photosynthesis. Over time, these prokaryotic cells became integrated into the host, evolving into the organelles we see today in eukaryotic cells.
• What evidence supports the endosymbiotic theory regarding the evolutionary origins of mitochondria and chloroplasts?
  • Several lines of evidence support the endosymbiotic theory. For instance, both mitochondria and chloroplasts contain their own circular DNA similar to that of bacteria, indicating a prokaryotic origin. Additionally, these organelles replicate independently of the cell through a process resembling binary fission. The double membranes surrounding these organelles also suggest an engulfment event, which is consistent with symbiotic relationships.
• Evaluate the impact of the endosymbiotic theory on our understanding of cellular evolution and biodiversity.
  • The endosymbiotic theory has significantly impacted our understanding of cellular evolution by illustrating how complex eukaryotic cells could arise from simpler prokaryotic ancestors. It highlights the role of symbiosis in evolutionary processes and contributes to our knowledge of biodiversity by explaining how different life forms can share cellular machinery for energy production and metabolism. This framework has reshaped biological classifications and our appreciation of the interrelatedness of all living organisms.

Related terms

Eukaryotes: Organisms whose cells have a nucleus enclosed within membranes, including animals, plants, fungi, and protists.

Mitochondria: Double-membrane-bound organelles found in eukaryotic cells that are responsible for producing ATP through cellular respiration.

Chloroplasts: Organelles found in plant cells and some protists that conduct photosynthesis, converting light energy into chemical energy stored in glucose.