Melanosomes are granules that produce melanin (a type of pigment) in animals and can be found in bird feathers. An ancient fossilized feather contains dark stripes made from preserved carbon structures similar in size and shape to melanosomes in modern feathers. Although skeptics have pointed out that ancient bacteria could leave carbon remains of the same size and shape, a prominent paleontologist argues that the structures in the feather are almost certainly melonosomes.
Which of the following, if true, would most help justify the prominent paleontologist’s judgment that the structures are almost certainly melanosomes?
A. Modern bird feathers rarely if ever contain the carbon remains of bacteria.
B. If the structures in the fossilized feather are melanosomes, they originally created stripes of pigmentation in the feather before it was fossilized.
C. Many other fossilized feathers also contain preserved carbon structures similar in size and shape to melanosomes.
D. Ancient bacteria of the size and shape of those carbon structures were commonly found in biological structures other than feathers.
E. Bacteria in a feather are almost always distributed fairly evenly throughout the feather, rather than in discrete stripes.
Solution
Passage Analysis:
| Text from Passage | Analysis |
| Melanosomes are granules that produce melanin (a type of pigment) in animals and can be found in bird feathers. | What it says: Melanosomes are tiny structures that make pigment and exist in bird feathers What it does: Sets up basic background knowledge about what melanosomes are What it is: Background/definitional information |
| An ancient fossilized feather contains dark stripes made from preserved carbon structures similar in size and shape to melanosomes in modern feathers. | What it says: Scientists found an old fossil feather with dark stripes made of carbon bits that look like melanosomes What it does: Introduces the specific fossil evidence that connects to the melanosomes we just learned about What it is: Factual observation/study finding Visualization: Fossil feather with dark stripes ā carbon structures that match melanosomes in size/shape |
| Although skeptics have pointed out that ancient bacteria could leave carbon remains of the same size and shape, a prominent paleontologist argues that the structures in the feather are almost certainly melonosomes. | What it says: Some people think these could be old bacteria remains (since they’d look the same), but an expert paleontologist strongly believes they’re melanosomes What it does: Presents the central disagreement and establishes the paleontologist’s confident position against the skeptical view What it is: Competing expert opinions/claims Visualization: Skeptics: Carbon structures = bacteria remains vs. Paleontologist: Carbon structures = melanosomes (both look identical) |
Argument Flow:
“We start with background info about melanosomes, then learn about fossil evidence that looks like melanosomes, and finally see that there’s a debate between skeptics (who think it’s bacteria) and a paleontologist (who’s confident it’s melanosomes)”
Main Conclusion:
“The prominent paleontologist believes the carbon structures in the fossil feather are almost certainly melanosomes (not bacteria)”
Logical Structure:
“The paleontologist’s conclusion is based on the similarity between the fossil carbon structures and modern melanosomes, but we need additional evidence to justify this confidence since bacteria would leave identical-looking remains”
Prethinking:
Question type:
Strengthen – We need to find information that would increase our belief in the paleontologist’s conclusion that the carbon structures are melanosomes rather than bacteria remains
Precision of Claims
The key claim is qualitative and categorical – the paleontologist argues the structures are ‘almost certainly melanosomes’ despite skeptics suggesting they could be bacteria remains. Both alternatives would leave identical carbon traces in terms of size and shape
Strategy
Since the main challenge is that bacteria and melanosomes would leave identical carbon remains, we need to find evidence that either:
- Shows these structures have characteristics that bacteria wouldn’t have
- Demonstrates the context or location makes melanosomes more likely than bacteria
- Provides additional evidence that supports the melanosomes interpretation over the bacteria interpretation
Answer Choices Explained
A. Modern bird feathers rarely if ever contain the carbon remains of bacteria.
This tells us that modern feathers don’t usually have bacterial carbon remains, but we’re dealing with an ancient fossilized feather. The conditions that preserve ancient fossils could be very different from what we see in modern feathers, so this doesn’t really help distinguish whether the ancient structures were melanosomes or bacteria.
B. If the structures in the fossilized feather are melanosomes, they originally created stripes of pigmentation in the feather before it was fossilized.
This is just stating what would be true if the structures were melanosomes – it’s circular reasoning. We’re trying to determine whether they ARE melanosomes, so saying ‘if they are melanosomes, then they created stripes’ doesn’t provide any new evidence to support that conclusion.
C. Many other fossilized feathers also contain preserved carbon structures similar in size and shape to melanosomes.
Finding similar structures in other fossilized feathers doesn’t help us determine whether these structures are melanosomes or bacteria. Both could be commonly preserved in fossils, so this evidence is neutral and doesn’t support either interpretation.
D. Ancient bacteria of the size and shape of those carbon structures were commonly found in biological structures other than feathers.
This actually weakens the paleontologist’s position! If ancient bacteria of this size and shape were commonly found in biological structures other than feathers, this makes it more likely that the structures could be bacteria remains, not melanosomes.
E. Bacteria in a feather are almost always distributed fairly evenly throughout the feather, rather than in discrete stripes.
This provides the key distinguishing evidence we need! If bacteria in feathers distribute evenly throughout the feather rather than in discrete stripes, then the fact that these carbon structures form distinct stripes strongly suggests they’re melanosomes (which create pigmentation patterns) rather than bacteria remains. This directly addresses why the paleontologist can be confident despite the size and shape similarity.
