Origines des cellules
Baccalauréat international · IB Diploma · Biology · HL Sujet 3 3:56 Narration en anglais · Sous-titres anglais + 中文 incrustés
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Mitochondria have their own DNA and divide within cells.
线粒体拥有自身的DNA，并在细胞内分裂。
These features invite an evolutionary explanation that can be tested against other evidence.
这些特征为一种可经其他证据检验的进化解释提供了依据。
The endosymbiotic model explains mitochondria and chloroplasts as descendants of bacteria living within another cell lineage.
内共生模型将线粒体和叶绿体解释为生活在另一细胞谱系内的细菌的后代。
Double membranes, ribosomes, DNA, and division provide several lines of evidence.
双层膜、核糖体、DNA和分裂方式为这一理论提供了多条证据。
This model is distinct from a complete explanation for the origin of the first life.
该模型并不等同于对最早生命起源的完整解释。
Endosymbiosis: One organism living within another in an evolutionary association.
内共生：一种生物生活在另一种生物体内，并在进化上形成关联的关系。
Inference: An explanation drawn from observations and reasoning.
推论：基于观察和推理得出的解释。
Independent observations strengthen a model when they make a consistent prediction.
当独立观察得出一致预测时，能够加强模型。
Similarity is evidence to evaluate alongside ancestry, sequence comparisons and alternative explanations, rather than proof from one feature.
相似性是与谱系、序列比对及替代解释并列的评估证据，而非单一特征所构成的证明。
In the lab: Use attributed micrographs and sequence data.
在实验室中，使用标注过的显微照片和序列数据。
Separate observations from inferences in a table.
在表格中将观察结果与推论分开。
Check whether each comparison concerns a mitochondrion, chloroplast, bacterial cell or eukaryotic nucleus.
检查每一项比较涉及的是线粒体、叶绿体、细菌细胞还是真核细胞核。
Known: 18 of 24 compared sequence sites are identical.
已知：在24个比较的序列位点中，有18个完全相同。
Identity equals 18 over 24, times 100, which is 75 percent.
一致性等于18除以24，乘以100，即75%。
Identity across this short alignment cannot alone date an evolutionary split or establish that one organism is the direct ancestor of another.
仅凭这段短比对的一致性，无法确定进化分歧的时间，也无法确立一个物种是另一个物种的直接祖先。
Your turn: 21 of 28 compared sites match.
轮到你了。 二十八处比对位点中有二十一处匹配。
Calculate percentage identity.
请计算序列一致性百分比。
Pause the video and work it out.
请暂停视频，自己算一算。
Check: 21 divided by 28 is 75 percent identity.
核对：21 ÷ 28，相同率为 75%。
The endosymbiotic model does not say that every organelle arose from an engulfed bacterium.
内共生模型并非指所有细胞器都起源于被吞噬的细菌。
A laboratory model of early chemistry is not a recreation of the whole historical event.
早期化学的实验模型并非对完整历史事件的复原。
Not true: One matching sequence proves the complete origin of life.
不正确。 一个匹配的序列并不能证明生命的完整起源。
One sequence match is one piece of evidence about one locus.
一个序列匹配只是关于一个位点的一项证据。
Origins models rest on many independent lines - DNA, ribosomes, membranes, biochemistry - not a single comparison.
起源模型建立在多条独立线索之上，包括DNA、核糖体、膜和生物化学，而非单一比较。
The endosymbiotic model explains mitochondria and chloroplasts as descendants of bacteria living within another cell lineage.
内共生模型将线粒体和叶绿体解释为生活在另一细胞谱系内的细菌的后代。
Independent observations strengthen a model when they make a consistent prediction.
当独立观察得出一致的预测时，就能加强该模型。
Watch for the endosymbiotic model does not say that every organelle arose from an engulfed bacterium.
请注意：内共生模型并非指所有细胞器都起源于被吞噬的细菌。
Sixteen out of twenty compared sequence sites are identical.
20个被比较的序列位点中有16个是相同的。
Find the percentage identity.
计算同一性百分比。
Say what that percentage does not prove.
说明该百分比不能证明什么。
The result is an identity of 80 percent.
结果是一致性为80%。
Mitochondria and chloroplasts have their own DNA and share features with bacteria.
线粒体和叶绿体有自己的DNA，并与细菌有共同特征。
Because several independent lines of evidence agree, the endosymbiotic model is well supported.
多条独立证据相互一致，因此内共生模型得到有力支持。
Sequence comparisons give 18 out of 24 and 30 out of 40 matching sites.
序列比对结果显示，匹配位点分别为 24 个中的 18 个和 40 个中的 30 个。
Compare identity; can one organism be declared the other's ancestor?
请比较同一性。 能否断定一个生物体是另一个生物体的祖先？
Both comparisons give 75 percent: 18 out of 24, and 30 out of 40.
两组比较的一致性都是 75%：24 个位点中 18 个相同，40 个位点中 30 个相同。
Short alignments and identity alone do not establish ancestry or dates; homologous loci, models and wider evidence are required.
较短的比对和一致性本身不能确定祖先关系或时间；还需要同源位点、模型和更广泛的证据。
Pause and check yourself. Explain each point on screen in your own words, then change one number in the last example and say which assumption must still hold.
暂停一下，自我检查：用自己的话解释屏幕上的每个要点，再改动最后一个例子中的一个数字，说明哪个假设仍然必须成立。