| There is an unbroken chain of life from the first cells on Earth to all cells in organisms alive today. |
| Understandings: |
Nature of science: |
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Cells can only be formed by division of pre-existing cells.
The first cells must have arisen from non-living material.
The origin of eukaryotic cells can be explained by the endosymbiotic theory.
https://www.youtube.com/watch?v=-FQmAnmLZtE
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Testing the general principles that underlie the natural world—the principle that cells only come from pre-existing cells needs to be verified. (1.9) |
| Applications : |
Guidance: |
| Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth. |
Evidence for the endosymbiotic theory is expected. The origin of eukaryote cilia and flagella does not need to be included.
Students should be aware that the 64 codons in the genetic code have the same meanings in nearly all organisms, but that there are some minor variations that are likely to have accrued since the common origin of life on Earth.
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| Skill: |
Theory of Knowledge |
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Biology is the study of life, yet life is an emergent property. Under what circumstances is a systems approach productive in biology and under what circumstances is a reductionist approach more appropriate? How do scientists decide between competing approaches? |
