PrepTest 112

Topic: Science

Paragraph 1

• Paragraph note
  • New discovery (hormones that maintain homeostasis play a role in sale and water consumption) challenges old focus (limit discussion of hormones' influence on behavior to gonadal hormones/sex)
• Views, minor Meta-Structures, and the author's attitude
  • Definition of "homeostasis": the physiological balance of body fluids (third sentence)
  • Definition of "osmolality": the concentration of solutes (fourth sentence)
  • New discovery:
    • Peptide and steroid hormones (which affect the body's homeostasis) can also influence water and salt consumption (second and third sentences)
  • Cause-and-effect relationship, according to the author:
    • Peptide and steroid hormones hormones regulate the body's homeostasis in inconsistent environments by causing animals to adjust their intake of water and sodium (even when deviations from normal homeostasis are quite small) (fourth and last sentences)
    • Osmolality is important for maintaining "stability" in the body when it's in an "inconstant external environment" (fourth sentence)
  • Author's attitude: "limited" (first sentence), "has now become clear" (first sentence), "play an important role" (third sentence), "achieved primarily" (fourth sentence)

Paragraph 2

• Paragraph note
  • How hormones maintain homeostasis (if osmolality decreases (more water), animals urinate; if it increases, animals thirst)
• Views, minor Meta-Structures, and the author's attitude
  • Definition of "vasopressin": a peptide hormone that promotes water conservation in the kidney" (fourth sentence)
  • Cause-and-effect relationship, according to the author:
    • Animals' bodies can handle little fluctuations of osmolality on their own, but when things get out of hand, the body secretes hormones to help maintain homeostasis (first and second sentences)
  • Examples of how hormones maintain homeostasis:
    • When osmolality decreases (too much water), the pituitary gland secretes vasopressin, which leads to urination and the inhibition of thirst (fourth and fifth sentences)
    • When osmolality increases (too little water), the pituitary gland releases vasopressin, which increases thirst (sixth sentence)
  • Comparison, according to the author:
    • Our threshold for becoming thirsty is higher than our threshold for urinating (last sentence)

Main Point: New research shows that certain hormones respond to osmolality and affect behaviors like salt and water consumption.

Phenomenon/Explanation: This passage utilizes a Phenomenon/Explanation Meta-Structure.* The phenomenon is "animal behavior" or, more specifically, "behaviors that regulate the homeostasis of animals' bodily fluids," and the explanation is "hormones influence the animal's behavior when the animal's osmolality deviates from the norm." Or, put more simply, the phenomena are "being thirsty and urinating," and the explanation is "animals' bodies notice when the concentration of water and sodium is out of whack, and hormones influence whether the animal will thirst for more water or urinate excess water."

When the passage utilizes a Phenomenon/Explanation Meta-Structure, the main point is generally the explanation if the author presents or endorses it. The author doesn't attribute the explanation to anyone else or criticize the explanation, so we surmise that the author supports the explanation. So, we summarized the main point as, "Certain hormones respond to osmolality and affect behaviors like salt and water consumption."

*Since the author writes to identify something that others have missed, we could have also identified this passage with a Correcting the Record or even an Old Approach/New Approach Meta-Structure. Classifying the passage this way could still lead to an effective understanding of the argument.

Example: As is the case for many science passages, there's a lot of cause and effect in this passage. However, we think the most important minor Meta-Structure are the two examples in the second paragraph. These examples are the keys to understanding the dense and jargon-filled passage. You may not have a clear understanding of what "osmoregulation" is or what it means that "minor fluctuations in the concentration of solutes in extracellular fluid" are "buffered by corresponding changes in the relatively larger volume of cellular water" (P2, S1). But, we can understand these examples and get a better grasp of what this passage is saying. In other words, these examples give us a clear picture of how animals' bodies maintain homeostasis and how hormones influence behavior. When there's too much water in the body, animals absorb vasopressin, which leads to urination and the inhibition of thirst (P2, S3-S4). When there's too little water, animals release releases vasopressin, which increases thirst (P2, S5). Hold on to these examples with both hands if you need to — they're helpful in understanding the main point!

Yeesh, this is a complicated science passage. It's full of technical jargon and complicated syntax. It seems like it's intended for advanced science students who are already familiar with peptides, hormones, and osmoregulation. For those of us who are less-than-fluent in science, we'll need to simplify the passage for ourselves. Try to start with the part that makes sense — as we discussed above, that's probably the two concrete examples in the second paragraph. Then, try to extrapolate what the entire passage is talking about from our understanding of that part. If we know that the concentration of water influences vasopressin, which influences thirst and urination, we can figure out how hormones influence behavior.