Passage Excerpt from “Research Riddle Resolved”
Excerpt from “Research Riddle Resolved”
For centuries, scientists were confounded by an animal that seemed to look and act like a combination of a bird, a reptile, and a mammal. It has a bill like a duck and lays eggs but produces milk for its young. It lives in a burrow, has fur, and can make venom. We now know that this animal is called a duck-billed platypus. A platypus is a monotreme, a type of egg-laying mammal.
Hundreds of years after the first sightings of the platypus, the animal still captures our imagination anew and irresistibly attracts the attention of science writers everywhere. The May 2008 Nature report detailing the DNA insides of the duck-billed platypus invited colorful tales from just about every mainstream media outlet.
But cuteness and weirdness aside, the platypus research results are a gold mine for medical researchers. The findings cement what may have seemed totally obvious but turned out to be a bit of a scientific surprise: platypus DNA is a patchwork of genes from reptiles, birds, and mammals.
Evolution Fusion
In other words, the platypus heritage is laid out in an evolutionary DNA tapestry that marks the time, hundreds of millions of years ago, when reptiles and mammals branched off the evolutionary tree.
So what? The platypus is nothing like a human, so what can its DNA tell us about people and the diseases we get?
Plenty, says an international team of scientists who did this work.
The platypus genome results are far more than confirmation of a scientific oddity. They provide researchers a window into a time in history when mammals became unique—gaining the ability to bear live young, produce milk for them, and grow a warm, furry coat.
That’s important because our own, modern-day genomes are still a big mystery and researchers need much more information to be able to translate our genetic language into useful health knowledge.
One of the ways scientists can decipher meaning from within our 3 billion DNA “letters,” or nucleotides, is to compare human genes with those from animals, to see what has been kept the same and what has evolved to be different. . . .
Same and Different
In an approach called comparative genomics, scientists compare the genome sequences of several species: human, mouse, and a wide variety of other organisms from single-celled fungi to elephants and, now, the platypus.
The goal of this research is to find regions of similarity and difference in order to better understand the structure and function of human genes.
Comparative genomics is directly related to evolution because all living things share a common ancestor. By using computer tools to examine genes that have been kept the same in many organisms over millions of years, researchers can locate signals that control how genes work. This information may translate into ways to understand, treat, and prevent human diseases. . . .
Chicken or Egg?
When researchers analyzed platypus DNA and compared it to that of chickens, snakes, and lizards, the findings traced the evolutionary path from birds and reptiles to mammals. They learned that the platypus lost most of its genetic ability to produce egg yolk—as compared to chicken genes. This suggests its departure from “chicken-ness.”
But, through evolutionary change, the platypus gained the ability to make milk that is rich in nutrients. Platypuses have genes that make the milk protein casein: just like we do.
A male platypus can, like its ancestral snake and lizard cousins, produce venom. The platypus ejects this venom through special glands in its back legs. The evolutionary reason for maintaining such molecular weaponry isn’t yet clear, but what is fascinating is that it appears nature mixed and matched together DNA pieces separately to create the venom genes in reptiles and monotremes like the platypus.
The scientific value of pinning genetics to physiological function—like milk production—is high. Such investigations may help medical researchers understand health issues related to reproduction and lactation. Although lactation is an ancient reproductive trait, mammals—including the platypus—are unique in their ability to produce milk that is extraordinarily nutritious, containing a rich blend of sugars, fats, and proteins.
More generally, though, studying how nature cuts and pastes gene modules gives scientists an inside scoop on how genetic changes relate to health and disease risk.
One thing is clear—the stunning blend of reptile, bird, and mammal puts the platypus in a class of its own, and it gives researchers much more: information about how mammals like us came about.
[Scientists’] genetic sleuthing of platypuses, chimps, fish, sunflowers—you name it—continues to teach scientists how millions of years of evolution progressed. This provides vital information to understanding the role of genes in the health and disease of mammals like us and our pets, and can also help preserve our rich and diverse planet.
From “Research Riddle Resolved”—Public Domain/National Institutes of Health
Question
The details in paragraphs 12–14 about the platypus’s different abilities convey a central idea of the excerpt by
- Ashowing that the platypus has a gene that allows it to produce nutrient-rich milk, as humans do.
- Bproving that the platypus, whose DNA is made up of DNA from several other species, has developed venom to defend itself.
- Csuggesting that the platypus, while gaining traits in common with mammals and reptiles, has lost some bird-like traits.
- Ddemonstrating that the platypus has a rare evolutionary background that includes bird, reptile, and mammal DNA.
Show the answer
Correct answer: D
The question asks how the details in paragraphs 12–14 about the platypus’s different abilities convey a central idea of the excerpt.
A. Incorrect. The fact that “platypuses have genes that make the milk protein casein” (paragraph 13) just like humans do is an important supporting detail, but it is not a central idea of the excerpt.
B. Incorrect. While paragraph 14 explains that the platypus produces venom “like its ancestral snake and lizard cousins,” which suggests the platypus has the ability to defend itself, this information is a supporting detail and not a central idea of the excerpt.
C. Incorrect. Paragraphs 12–14 do state that the platypus has lost some of its “chicken-ness” (paragraph 12) while gaining traits in common with mammals and reptiles, but this information is a supporting detail and not a central idea of the excerpt.
D. CORRECT. In describing the platypus’s different abilities, paragraph 12 states that “the findings traced the evolutionary path from birds and reptiles to mammals.” Paragraphs 12–14 elaborate on the findings to support a central idea of the excerpt, which is that the platypus is rare in having bird, reptile, and mammal DNA.
Question analysis
In “Research Riddle Resolved,” three paragraphs report what platypus DNA reveals about the animal’s egg yolk, milk and venom. This central-idea question asks how those findings serve a central idea of the whole excerpt, so students must first decide what that idea is and then see how separate abilities point to it.
- Grade level
- Grade 8 reading and task
- Compared with grade 7
- At grade 7 The skill of tying details to a central idea is ordinary for grade 7, and the task stays at that level; what slows students is genetic vocabulary such as “casein” and “molecular weaponry” in a long science article.
- Estimated difficulty
- Moderate: several steps, or a close reading with one strong distractor.
- Thinking it demands
- Depth of knowledge 2, skills and concepts · mainly analyze
- What makes it hard
- A very close wrong answer moderate
- Evidence in several places moderate
- Hard words minor
- Evidence
- Answered from several paragraphs or stanzas
- Reading level
- Passage: about grade 11, 809 words; question and choices: about grade 11, 89 words.
- Corrected from the DOE handbook
- A stray colon in a quotation in the explanation was removed.
- Students, last 30 days
- Not enough answers yet to show (it takes 10).
Why it is hard, traps and wrong answers (shows the answer)
Why it is hard
Because each wrong choice is drawn from paragraphs 12–14, checking the choices against those paragraphs alone confirms nearly all of them. The question is about the level of the claim: the excerpt keeps returning to the platypus as a blend of bird, reptile and mammal, and the yolk, milk and venom findings are examples of it. The choice listing what was lost and gained is hardest to set aside, since it states the same mixture as separate findings rather than the idea behind them.
A very close wrong answer moderate Choosing the answer
The gains-and-losses choice and the key both describe the platypus’s bird, reptile and mammal heritage; one lists what paragraphs 12–14 report, the other names the rare blend the excerpt keeps returning to. (Embretson & Wetzel, 1987; Gorin & Embretson, 2006; Ascalon et al., 2007)
Evidence in several places moderate Working it out
The central idea is stated far from these paragraphs, as a “patchwork of genes” in paragraph 2 and a “stunning blend of reptile, bird, and mammal” in paragraph 17, and must be tied back to them. (Kirsch & Mosenthal, 1990; Gorin & Embretson, 2006)
Hard words minor Understanding the question
The three paragraphs rely on “casein,” “monotremes,” “molecular weaponry” and the coined “chicken-ness,” and each finding has to be decoded before students can see what the three share. (Perfetti, 2007; Freedle & Kostin, 1993)
Strategy: Ask what the yolk, milk and venom findings have in common, then check that the option you choose describes that shared point rather than any single finding.
Traps
- Too narrow: A single detail offered as the central idea or a summary, or a summary that keeps minor details and leaves out an essential part.
- Outside knowledge: A choice is plausible in the real world but not supported by this text.
The wrong answers, classified
A Too narrow (King et al., 2004)
Picks paragraph 13’s milk protein casein, which platypuses share with humans, an accurate detail, but one finding alone does not convey the idea that all three paragraphs build.
B Outside knowledge (King et al., 2004; Recht & Leslie, 1988)
Assumes venom must be for self-defense, as it is in many animals, though paragraph 14 says the reason for keeping such “molecular weaponry isn’t yet clear.”
C Too narrow (King et al., 2004)
Correctly sums up the findings, yolk genes lost and milk and venom genes present, but stays at the level of details and never reaches the rare mixed ancestry they point to.
What was corrected from the DOE handbook, and why
- Explanation: The handbook’s explanation of Option A quotes paragraph 13 as “platypuses have genes that make the milk protein casein: ”(paragraph 13), carrying into the quotation the colon that follows “casein” in the passage and setting the closing quotation mark apart from the word. The site now reads “platypuses have genes that make the milk protein casein” (paragraph 13), as the DOE’s later printing of this explanation does.
Working it out, step by step
Figure out what the question asks
This asks how the details in paragraphs 12–14 support a central idea. A central idea is a main point the whole excerpt keeps making. So first find that idea. Then see how the details point to it.
Find the central idea
Paragraph 2 says “platypus DNA is a patchwork of genes from reptiles, birds, and mammals.” A patchwork is something made of many different pieces. Near the end, paragraph 17 says “the stunning blend of reptile, bird, and mammal puts the platypus in a class of its own.” So a central idea is the platypus’s rare mix of bird, reptile and mammal genes.
Sort the details in paragraphs 12–14
- Birds: compared with chickens, the platypus “lost most of its genetic ability to produce egg yolk” (paragraph 12).
- Mammals: “Platypuses have genes that make the milk protein casein” (paragraph 13), as people do.
- Reptiles: a male can make venom, “like its ancestral snake and lizard cousins” (paragraph 14).
Each detail links the platypus to a different group of animals.
Check each choice
- A does not fit. The milk is one detail from paragraph 13. One detail is not the central idea.
- B does not fit. Paragraph 14 says the reason for the venom “isn’t yet clear.” Nothing proves it is for defense.
- C does not fit as well. It lists gains and losses, but it stays with the details. It never says what they add up to.
- D fits. Together, the details show a rare background that mixes bird, reptile and mammal DNA.
Choose the answer
Watch out: C is true to paragraphs 12–14, so it is tempting. But the question asks for the central idea the details show, and C only retells them. So the answer is D.
Why this answer and not the closest wrong one
C is the closest wrong answer. C and D describe the same traits. C lists them: bird traits lost, mammal and reptile traits gained. D names what they add up to, a rare mix of bird, reptile and mammal DNA. The excerpt makes that point in paragraphs 2 and 17, so D shows the central idea.
More questions like this
The original DOE question
The passage “Excerpt from “Research Riddle Resolved”” as printed (pages 66–67)
