Based solely on the evidence provided in the prelab activity, which organism is most closely related to LECA and why?Note: Please refer to your prelab activity to help answer this question. Definitions of LECA and FECA can be found in Week 4 content.

Question

BlackTom AI · Accepted Answer

LECA was a unicellular ancestor of all eukaryotes that already possessed key eukaryotic features (a nucleus, endomembrane system, mitochondrion from endosymbiosis). Multicellularity evolved independently in many eukaryotic lineages long after LECA.

1) Relevant knowledge points and concepts
- LECA (Last Eukaryotic Common Ancestor) is inferred to be a unicellular eukaryote with core eukaryotic cellular machinery.  
- Multicellularity is a derived trait that appeared multiple times independently in eukaryotes (animals, plants, fungi, some protists).  
- Determining closeness to LECA requires phylogenomic or molecular evidence (shared gene content, conserved molecular characters), not superficial body plans of extant multicellular animals.

2) Step-by-step reasoning
- Step 1: Identify organisms offered in the prelab: sea star, fish, isopod (all are multicellular animals).  
- Step 2: Compare those to LECA: LECA was unicellular. None of the provided organisms share that basic characteristic.  
- Step 3: Conclude that morphological or ecological similarity among multicellular animals does not indicate proximity to a unicellular ancestor.  
- Step 4: Recognize the kind of evidence needed (molecular phylogenies, presence/absence of ancestral genes, cellular structures) is absent from the provided prelab evidence.

3) Calculations
- Not applicable; this is a comparative/phylogenetic reasoning problem.

4) Why the correct answer is correct
- Because all choices presented are extant multicellular animals and LECA is reconstructed as a unicellular eukaryote, the prelab evidence (which only shows multicellular animals) cannot identify which is most closely related to LECA. Only molecular phylogenetic data including unicellular lineages could resolve closeness to LECA.

5) Why other options are incorrect (briefly)
- a and e (sea star): sea stars are multicellular echinoderms, not colonies of independent cells approximating LECA; radial symmetry is a derived body plan, not an ancestral eukaryotic trait.  
- b (fish): vertebrates are highly derived multicellular animals; aquatic habit does not make them closer to LECA.  
- d (isopod): arthropods are also complex, derived multicellular animals; “simplicity” of appearance is not evidence of closeness to a unicellular ancestor.

6) Conclusion confirming the answer
- Therefore, the correct choice is option c: This cannot be determined using the evidence provided, because all organisms provided are multicellular animals, while LECA was unicellular.

Based solely on the evidence provided in the prelab activity, which organism is most closely related to LECA and why?Note: Please refer to your prelab activity to help answer this question. Definitions of LECA and FECA can be found in Week 4 content.单项选择题

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