Question

there are several questions about this passage.
reading passage excerpt... pauling (1901 - 1994) was an american scientist. he studied dna, the material that carries a living organism’s genetic information.
from the shape of dna
like most other scientists, pauling was not interested in dna until 1952, even though swiss biologist friedrich miescher had discovered dna in 1869. but what was dna? scientists knew only a little. it came in long strands, and each strand had a phosphorus - sugar backbone. there were also nucleic bases, which stuck out from the backbone like knobs on a spine. but the shape of the strands and how they linked up were mysteries—important mysteries, as pauling showed with hemoglobin: shape can affect how molecules work. soon the shape of dna became the most important question in biology.
and pauling, like many others, assumed he was the only one smart enough to answer this question. this wasn’t, or at least wasn’t only, arrogance: pauling had simply never been beaten before. so in 1952, pauling sat down at his desk in california to crack dna. he decided, incorrectly, that the bulky nucleic bases sat on the outside of each strand with the phosphorus - sugar backbone toward the molecule’s core. pauling also reasoned that dna was a triple helix, with three ribbons of the phosphorus - sugar backbones forming a spiral. unfortunately for pauling, his data came from a dried - out dna sample, which made the molecule seem more complicated. but on paper, all this seemed possible.
everything was humming along nicely until pauling asked a graduate student to check his calculations. the student did, and was soon tying himself in knots trying to see where he was wrong and where pauling was right. eventually, the student pointed out to pauling that something about his theory didn’t seem quite right.
choose two ways the illustration after paragraph 9 best clarifies information for the reader.

1. the illustration explains how important the phosphorus - sugar backbone is in dna.
2. the illustration reveals the actual names of the four bases discussed in the passage.
3. the illustration supports the idea of why dna is sometimes referred to as a kind of blueprint.
4. the illustration provides a concrete example of what the widely accepted dna model looks like.
5. the illustration details the importance of the four bases and why they fit snugly with the backbone.

Explanation:

1. Analyze Option 2: The passage mentions nucleic bases but not their actual names. An illustration of DNA would likely show the names of the four bases (adenine, thymine, cytosine, guanine), so this is a valid way it clarifies.
2. Analyze Option 4: The passage discusses the DNA model (triple helix idea of Pauling, though incorrect, and the general structure). An illustration would provide a concrete example of the widely accepted DNA model (double helix), helping readers visualize it.
3. Eliminate other options:

• Option 1: The passage doesn't emphasize the importance of the backbone, so the illustration likely doesn't explain this.
• Option 3: The passage doesn't connect DNA to a blueprint idea, so the illustration wouldn't support this.
• Option 5: The passage doesn't detail why the bases fit with the backbone, so the illustration wouldn't do this.

Answer:

1. The illustration reveals the actual names of the four bases discussed in the passage.
2. The illustration provides a concrete example of what the widely accepted DNA model looks like.