Examkin

Question

Difficulty: MediumEvaluating the Impact of New Evidence

### Origin of Organelle X

Two hypotheses are proposed to explain the evolutionary origin of Organelle X, a compartment found in the cytoplasm of the single-celled eukaryote *Protistum novum*.

*Hypothesis 1*
Organelle X originated through endosymbiosis. An ancestral eukaryotic host cell engulfed a photosynthetic cyanobacterium. Instead of being digested, the bacterium lived symbiotically inside the host, eventually evolving into Organelle X. According to this hypothesis, Organelle X contains its own circular DNA and protein-synthesis machinery similar to that of free-living bacteria.

*Hypothesis 2*
Organelle X originated through membrane invagination. The outer cell membrane of an ancestral eukaryotic cell folded inward and pinched off, creating an internal vesicle that specialized over time into Organelle X. According to this hypothesis, Organelle X does not contain its own DNA; all of its structural and functional proteins are encoded by the cell's nuclear DNA.

Suppose scientists analyze the molecular composition of Organelle X and discover that it contains circular DNA molecules and ribosomes that are sensitive to the same antibiotics that inhibit bacterial translation. Which hypothesis is supported by this new finding?

  1. A
    Hypothesis 2, because the presence of genetic material inside the organelle confirms that it developed from the host cell's membrane invaginations.
  2. B
    Both Hypothesis 1 and Hypothesis 2, because both hypotheses require the organelle to have its own independent translation machinery to function properly.
  3. Hypothesis 1, because the presence of circular DNA and bacterial-like ribosomes is consistent with the characteristics of an engulfed symbiotic bacterium.Answer
  4. D
    Neither Hypothesis 1 nor Hypothesis 2, because the sensitivity to antibiotics indicates that the organelle is a modern contaminant rather than an evolutionary structure.

Answer

Hypothesis 1 is supported because the presence of independent circular DNA and bacterial-like ribosomes matches the characteristics of an engulfed bacterial cell, which contradicts the prediction of Hypothesis 2.
The correct answer is correct because the new evidence (finding circular DNA and bacterial-like ribosomes) matches the specific predictions of the endosymbiotic model described in Hypothesis 1, which states that the organelle should contain its own circular DNA and protein-synthesis machinery.

Step-by-Step Solution

1
Analyze the core predictions of both hypotheses regarding Organelle X's internal composition.
Hypothesis 1 predicts the presence of circular DNA and bacterial-like protein-synthesis machinery. Hypothesis 2 predicts the absence of DNA, as all proteins should be encoded by the nucleus.
To establish the criteria for evaluating the new evidence against each model.
2
Evaluate the new scientific finding.
The new evidence reveals that Organelle X contains circular DNA and ribosomes sensitive to bacterial antibiotics.
To identify which set of predictions matches the empirical data.
3
Determine the impact of the evidence on the two hypotheses.
The presence of circular DNA and bacterial-like translation components matches the predictions of Hypothesis 1 and contradicts Hypothesis 2.
To draw the correct conclusion regarding support for the hypotheses.

Key Concept

Evaluating the Impact of New Evidence
Estimated Time:1m 30s
Rate this question

Topics

Evaluating the Impact of New Evidence

More questions from this topic