Endosymbiotic Theory and Scientific Theories

Understanding Scientific Theories

• Scientific theories differ from everyday use of the term "theory".
• In science, a theory is not an educated guess but an explanation supported by evidence.
• Theories must be testable and repeatedly tested.
• Even though theories can change or be disproven, they are based on facts.

Prokaryotes vs. Eukaryotes

• Prokaryotes:

  • "Pro" rhymes with "NO": No nucleus, No membrane-bound organelles.
  • Example: Bacteria.
  • Shared features with eukaryotes: Cell membrane, cytoplasm, ribosomes, genetic material.

• Eukaryotes:

  • "Eu" rhymes with "DO": They DO have a nucleus and other membrane-bound organelles.
  • More complex than prokaryotes.

Endosymbiotic Theory

• Explains evolution of eukaryotic cells from prokaryotic cells.
• Concept:
  • Ancient large prokaryotic cells engulfed smaller bacteria.
  • Instead of being digested, engulfed bacteria lived symbiotically within the host cell.
• Evolutionary Steps:
  • Ancestor Heterotroph Eukaryote: Large cells engulfed bacteria that could produce energy using oxygen.
  • Ancestor Autotroph Eukaryote: Some cells also engulfed photosynthetic bacteria.
• Modern Consequences:
  • Mitochondria evolved from bacteria that used oxygen to produce ATP.
  • Chloroplasts evolved from photosynthetic bacteria.

Supporting Evidence

• Mitochondria and chloroplasts have their own DNA separate from nuclear DNA.
• DNA structure similar to bacterial (prokaryote) DNA.
• Size and division of mitochondria/chloroplasts resemble bacteria.

Importance and Further Exploration

• Endosymbiotic theory provides insight into the evolution of eukaryotic cells.
• Secondary Endosymbiosis could offer explanations for other organelles.
• Endosymbiosis occurs today, example: Termites with gut bacteria aiding wood digestion.

Conclusion

• Endosymbiosis isn't just a historical theory; it's a process observed in modern-day organisms.
• Encouragement to continue exploring such scientific phenomena.