Origins of cells: evidence and limits
도입됨| English | 의미 |
|---|---|
| endosymbiosis/ˌendəʊˌsɪmbaɪˈəʊsɪs/ | 내공생 |
| inference/ˈɪnfərəns/ | 추론 |
What would explain this observation?
- Mitochondria have their own DNA and divide within cells. These features invite an evolutionary explanation that can be tested against other evidence.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- The endosymbiotic model explains mitochondria and chloroplasts as descendants of bacteria living within another cell lineage. Double membranes, ribosomes, DNA and division provide several lines of evidence. This model is distinct from a complete explanation for the origin of the first life.
- endosymbiosis 内共生: One organism living within another in an evolutionary association; inference 推论: An explanation drawn from observations and reasoning.
Which observation is relevant evidence for mitochondrial endosymbiosis?
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Mitochondria carrying their own DNA - bacterial-style, with their own ribosomes - is exactly what an engulfed-bacterium origin predicts. Equal cell sizes or a nucleus in every organelle are not observations and would not test the model.
Match each technical term to its precise meaning.
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Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Independent observations strengthen a model when they make a consistent prediction. Similarity is evidence to evaluate alongside ancestry, sequence comparisons and alternative explanations, rather than proof from one feature.
- Use attributed micrographs and sequence data. Separate observations from inferences in a table. Check whether each comparison concerns a mitochondrion, chloroplast, bacterial cell or eukaryotic nucleus.
Which two habits make the investigation or model in this case more defensible?
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Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: 18 of 24 compared sequence sites are identical. Identity = 18/24 × 100 = 75%. Identity across this short alignment cannot alone date an evolutionary split or establish that one organism is the direct ancestor of another.
21 of 28 compared sites match. Calculate percentage identity. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
21 of 28 compared sites match. Calculate percentage identity.
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The result is 75 %. Known: 21 of 28 sites match. Use percentage identity = matches / sites x 100. Identity = 21/28 x 100 = 75%. A short-alignment percentage cannot by itself date a split or prove direct ancestry.
Check the conclusion and its limits
- The endosymbiotic model does not say that every organelle arose from an engulfed bacterium. A laboratory model of early chemistry is not a recreation of the whole historical event.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
One matching sequence proves the complete origin of life. This claim is false: One sequence match is one piece of evidence about one locus. Origins models rest on many independent lines - DNA, ribosomes, membranes, biochemistry - not a single comparison.
Origins of cells: evidence and limits: Independent observations strengthen a model when they make a consistent prediction. Similarity is evidence to evaluate alongside ancestry, sequence comparisons and alternative explanations, rather than proof from one feature.
One matching sequence proves the complete origin of life.
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One sequence match is one piece of evidence about one locus. Origins models rest on many independent lines - DNA, ribosomes, membranes, biochemistry - not a single comparison.
One organism living within another in an evolutionary association: write the technical term.
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endosymbiosis means One organism living within another in an evolutionary association.