Endosymbiosis - Cells within cells: An extraordinary claim

The idea that mitochondria once existed as free living bacteria and that a cell (or cells) engulfedanother prokaryote cell which was not digested but became an organelle inside a eukaryote cellmillions of years ago is a difficult idea to ‘prove’. (The scientific method doesn’t prove theories withcertainty like mathematics, it uses evidence to support an idea until it is falsified by new evidence.)This story of a biologist’s research over sixteen years illustrates some important ideas about thenature of science.

Key ideas about the nature of science

  • Science can test hypotheses about events that happened long ago.
  • Scientific ideas are tested with multiple lines of evidence.
  • Science is a community endeavour - new discoveries depend on the scientific community.
  • Scientific ideas evolve with new evidence.
  • The scientific method can overcome individual biases.

Part A: Endosymbiosis Case Study

The word symbiosis literally means the “living together more or less intimate association or close union of two dissimilar organisms” according to the Merriam-Webster Online Dictionary. Endo refers to internal, and thus endosymbiosis refers to an internal “living together” within a single organism. The process of endosymbiosis is observed often in biology, for example a variety of marine coral species hold bacteria species that photosynthesize and thus provide energy for the coral; this is only one example of many examples.

In this case study you will examine the concept of endosymbiosis and the concepts connection to the development of eukaryotic cells. The case study is provided by UC Berkeley which can be foundhere.

  1. Describe symbiosis:
  1. Name and briefly describe the three types of symbiosis:
  1. Draw a diagram to summarize endosymbiosis
  1. Describe three types of evidence for Eukaryotes forming by endosymbiosis
  1. Membranes:
  1. DNA:
  1. Reproduction:
  1. What does the evidence suggest for the presence of chloroplast in some cells but not in others?

Part B:McGraw-Hill Endosymbiosis Animation

  1. What type of transport does the development of Eukaryotes by endosymbiosis represent?
  1. What does the animation provide as evidence for endosymbiosis?
  1. Where does the animation suggest mitochondria and chloroplasts were derived from?