Topic 1.5 The Origin of CellsIB Biology

R. Price

v. 1 2015

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Cells can only be formed by division of pre-existing cells

Evidence:• No natural mechanism to

produce cells from simpler subunits• No example of cell number

increasing without cell division• Viruses are produced from

simpler subunits but not made of cells and can only reproduce inside host cells

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The first cells must have arisen from non-living material

Where did the first cells come from?Hypothesis: • A series of stages over long

periods of time• Evolved over a period of

hundreds of millions of years

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The origin of eukaryotic cells can be explained by the endosymbiotic theory

• Explanation for mitochondria, chloroplasts, and mDNA & ctDNA• Mitochondria & chloroplasts

were once free-living protists• Taken in by larger protists• Mutualistic relationship

Smaller cell supplied w/food or resources

Larger cell supplied w/ energy

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Sources

Content Allott, Andrew, and David Mindorff. Biology: Course Companion. 2014 ed. Oxford: Oxford UP, 2014. Print. Oxford IB Diploma Programme.

Walpole, Brenda. Biology for the IB Diploma. 2nd ed. Cambridge: Cambridge UP, 2014. Print.

ImagesUnless otherwise noted, images are obtained from Pixabay (www.pixabay.com) and used under the CC0 Public Domain license.