Scientific Theories and the Endosymbiotic Theory

Understanding Scientific Theories

• Scientific theories: Not just educated guesses, but explanations of scientific events, supported by evidence and repeated testing.
  • They can be changed or disproven.
  • Example theories: General Theory of Relativity, Atomic Theory, Cell Theory.

Endosymbiotic Theory

• Definition: Explains how eukaryotic cells evolved from prokaryotic cells through symbiotic relationships.

Characteristics of Cells

• Prokaryotes:
  • No nucleus or membrane-bound organelles.
  • Contain a cell membrane, cytoplasm, ribosomes, and genetic material.
• Eukaryotes:
  • Have a nucleus and membrane-bound organelles.
  • Share fundamental cell structures with prokaryotes.
• Difference: Eukaryotes are more complex than prokaryotes.

Evolutionary Process

• Occurred over 2 billion years ago.
• Prokaryotes:
  • Some had photosynthetic abilities (photosynthetic bacteria).
  • Some could use oxygen to produce ATP energy.
  • Larger ones could engulf others.
• Endosymbiotic Theory Explanation:
  • Large prokaryotes engulfed smaller bacteria.
  • Smaller bacteria lived as symbionts inside the larger cells.
  • Ancestor heterotroph eukaryote formed.
  • Some cells also engulfed photosynthetic bacteria, leading to ancestor autotroph eukaryotes.

Mitochondria and Chloroplast Evolution

• Mitochondria:
  • Evolved from bacteria that produced ATP using oxygen.
• Chloroplasts:
  • Evolved from bacteria that used sunlight for photosynthesis.
• Sequence: Mitochondria likely developed first, as all eukaryotes have them, while only some also have chloroplasts.

Supporting Evidence

• Mitochondria and chloroplasts have their own DNA, arranged like bacterial DNA.
• Size and division method of mitochondria and chloroplasts are similar to bacteria.

Modern Endosymbiosis

• Current occurrence: Endosymbiosis is ongoing with various organisms today.
• Example: Termites have prokaryotes in their gut aiding in wood digestion.

Conclusion

• Endosymbiotic theory provides key insights into the evolution of eukaryotes from prokaryotes.
• Encouragement to explore further, especially concepts like secondary endosymbiosis.