Passage Reference: For a long time, researchers in the field believed that anaesthetics worked by dissolving in the fatty sheaths that insulate nerves. This, it was theorized, caused them to interfere with the electrical signals that pass along those nerves. Since one of the few things that anaesthetic chemicals seemed to have in common was a tendency to dissolve in fats, and their solubility was related to their effectiveness, that hypothesis looked good until the suggested electrical effects were measured in the 1980s and discovered to be too small.

Tips: If a paragraph talks about an idea being accepted in the past and later rejected, look for a heading about an earlier hypothesis.

Why the other options are wrong:

• Proteins might play a part in anaesthesia: Proteins are not the focus here. This paragraph is about fatty sheaths and electrical signals, so this is a wrong section trap.
• Two conflicting theories: Only one old theory is explained here, not a comparison. This is a partial truth trap.

Key Vocabulary:

• sheaths = outer coverings
• hypothesis = theory

Question Focus: Main idea - a newer theory involving proteins

Passage Reference: . At around that time, however, another idea was becoming popular. This was that anaesthetics combine with critical proteins in the central nervous system and bring them — and consciousness — grinding to a halt. Subsequent research has shown that anaesthetics can, indeed, bind to protein molecules, and can sometimes affect their function as a result. But nobody has yet identified the elusive proteins involved in anesthesia. In October, however, Roderic Eckenhoff, an anesthesiologist at the University of Pennsylvania, will publish a paper that may bring that identification closer. Though he has not found the guilty proteins, he thinks he knows something important about their characteristics, and thus how anaesthetics perform their trick.

Why this is correct: The paragraph introduces the idea that anaesthetics work by interacting with proteins in the central nervous system. This is clearly the main theme.

Tips: When a paragraph introduces a new idea, choose a general heading, not one about results or details.

Why the other options are wrong:

• Dr. Eckenhoff's theory: His specific theory is developed later. Here, proteins are discussed in general, so this is a wrong section trap.
• Findings made by Dr. Eckenhoff: This paragraph introduces his work but does not describe results yet. That comes later. This is a time/tense trap.

Key Vocabulary:

• elusive = hard to find
• bind = attach

Question Focus: Main idea - basic description of protein structure

Passage Reference: D. Proteins consist of long chains of chemical links known as amino acids. These chains, however, are usually folded up into more or less globular shapes which are held steady by weak chemical bonds between adjacent parts of the chain.

Why this is correct: This paragraph is purely descriptive, explaining what proteins look like and how they are shaped. There is no discussion of anaesthesia yet.

Tips: Background science paragraphs usually match simple, factual headings.

Why the other options are wrong:

• Dr. Eckenhoff's theory: No theory is mentioned here, only basic background information. This is an example-as-main-idea trap.
• How to measure a protein's destabilization: Measurement is discussed later, not here. This is a wrong section trap.

Key Vocabulary:

• globular = ball-shaped
• adjacent = next to

Question Focus: Main idea - his explanation of how anaesthetics affect proteins

Passage Reference: E. Since the shape of a protein is critical to its function (particularly if it has a precisely sculpted docking port for other molecules to enter), Dr. Eckenhoff suspected that anaesthetics work by changing the stability of the folding of a particular protein, thus affecting how well that protein does its job. Anaesthetics might achieve this either by making the shape of a protein so stable that it cannot flex in response to docking and undocking molecules, or so unstable that the docking port loses its shape. The test of this theory, to be published in October’s Molecular Pharmacology, looked at two proteins (albumin and myoglobin) which have nothing directly to do with anaesthesia, but which are easy to extract in large quantities for experiments.

Why this is correct: The paragraph clearly explains Dr. Eckenhoff’s own idea about protein folding and how anaesthetics affect it.

Tips: Look for names like Dr. X suspected to spot a theory heading.

Why the other options are wrong:

• Findings made by Dr. Eckenhoff: This paragraph explains a theory, not results. The experiments come later. This is a time/tense trap.
• Two conflicting theories: Only one theory is described here. This is a partial truth trap.

Key Vocabulary:

• stability = how steady something is
• dock = attach

Question Focus: Main idea - results from his earlier experiments

Passage Reference: F. Dr. Eckenhoffs previous work has shown that when an anaesthetic molecule such as isoflurane binds to albumin (a component of blood), the protein becomes more settled in its folded pattern. This means that anaesthetics are less likely to stick to it if it is destabilized.

Why this is correct: This paragraph reports what his experiments showed, comparing albumin and myoglobin. These are clearly findings, not theories.

Tips: Words like has shown usually signal experimental findings.

Why the other options are wrong:

• Effect of the two variables on proteins: Temperature and pressure are not discussed here. This is a wrong section trap.
• The proteins have albumin-like qualities: That conclusion comes later. Here, results are being described. This is a context shift trap.

Key Vocabulary:

• bind = attach
• destabilized = made less stable

Question Focus: Main idea - temperature and pressure effects

Passage Reference: .

G. Since it is one of the characteristics of anaesthesia that its effectiveness weakens with temperature and pressure, Dr. Eckenhoff wanted to examine the effects of these two variables on the proteins in question. Raising the temperature destabilized both proteins (no great surprise, given that molecules, shake more when they are hotter). So did increasing the pressure. But Dr. Eckenhoff was able to measure the precise amount of destabilization by carrying the experiments out in water containing a radioactive form of hydrogen called tritium.

Why this is correct: The whole paragraph focuses on how temperature and pressure affect protein stability.

Tips: When numbers or conditions are tested, look for headings about effects or variables.

Why the other options are wrong:

• How to measure a protein's destabilization: Measurement details are explained in the next paragraph. This is a wrong section trap.
• Findings made by Dr. Eckenhoff: This is about experimental conditions, not final findings. This is a partial truth trap.

Key Vocabulary:

• variables = factors
• destabilized = made less stable

Question Focus: Main idea - method of measurement

Passage Reference: m.

H. In the normal course of events, a protein molecule will swap hydrogen atoms with the surrounding water from time to time — and if that molecule has been partially unfolded, there will be more hydrogen available to swap, since atoms on the inside as well as the outside of the globule will be available for exchange. The extent to which a protein has been destabilized can, therefore, be measured by how radioactive it becomes in a given period of time.

Why this is correct: This paragraph explains the method used to measure how unstable a protein is.

Tips: Headings starting with How to usually match method paragraphs.

Why the other options are wrong:

• Effect of the two variables on proteins: Variables are not tested here, only measurement explained. This is a context shift trap.
• Shapes of proteins: Protein shape is not the focus. This is a wrong section trap.

Key Vocabulary:

• radioactive = giving off energy
• exchange = swap

Question Focus: Main idea - comparison showing similarity to albumin

Passage Reference: me.

I. The stability curves for an albumin at different temperatures and pressures turn out to have the same sort of shape as the curves for the effectiveness of anaesthetics (those of myoglobin do not match at all). And two other lines of evidence from the paper also indicate that the proteins involved in anaesthesia have albumin-like qualities.

Why this is correct: The paragraph concludes that the proteins involved behave like albumin, based on stability curves.

Tips: Conclusion-style sentences often signal the main idea.

Why the other options are wrong:

• The two evidences showing the proteins' aibumin-like quality: The details of the two evidences are explained next, not here. This is a wrong section trap.

Key Vocabulary:

• curves = graphs
• qualities = characteristics

Question Focus: Main idea - two supporting pieces of evidence

Passage Reference: ies.

J. One is that only albumin responds to changes in the concentration of isoflurane in the way that would be predicted if it were acting like a protein responding to anaesthesia. The other is the response of albumin to different forms of isoflurane.

Why this is correct: The paragraph clearly lists two pieces of evidence supporting the albumin comparison.

Tips: Words like one and the other often match headings about multiple evidences.

Why the other options are wrong:

• Different potency of isofluranes' two varieties: That specific detail is expanded in the next paragraph. This is an example-as-main-idea trap.

Key Vocabulary:

• responds = reacts
• predicted = expected

Question Focus: Main idea - comparison of two forms of isoflurane

Passage Reference: rane.

K. The isoflurane molecule comes in two varieties, which are mirror images of each other. For most chemical purposes the varieties are identical, but anaesthesia can tell the difference — and one is more potent than the other. Dr. Eckenhoff has found that the more potent variety binds more strongly to albumin, but not to myoglobin.

Why this is correct: This paragraph focuses entirely on the difference in strength between two forms of isoflurane.

Tips: When a paragraph compares two versions, choose a comparison heading.

Why the other options are wrong:

• Findings made by Dr. Eckenhoff: This is too general. The paragraph is about one specific finding. This is a partial truth trap.

Key Vocabulary:

• potent = strong
• varieties = types

Question Focus: Main idea - unanswered questions remain

Passage Reference: lobin.

L. Anaesthesia, therefore, seems to work by stabilizing rather than destabilizing critical proteins. But which ones? The most likely candidates are the protein receptors of the small chemical messengers (known as neurotransmitters) which carry signals, from one nerve cell to another at special sites called synapses. Work on glutamate receptors, which are responsible for simulating the brain, suggests that these are, indeed, inhibited by anaesthetics. But in contrast to this, John Mihic of the University of Colorado and his colleagues have recently made a case for anaesthetics working by increasing rather than decreasing the effects of receptor molecules — in this case the receptors for GABA and glycine, two neurotransmitters that calm down excited synapses. How that fits in with the Eckenhoff model remains to be seen. Clearly, however, anaesthesia has not given up all of its s

Why this is correct: The paragraph presents two opposing views: one group says anaesthetics work by inhibiting glutamate receptors, while Mihic's team argues they work by increasing the effects of GABA and glycine receptors. The passage ends saying anaesthesia has not given up all of its secrets. These are clearly two conflicting theories.

Tips: Look for phrases like remains to be seen to spot uncertainty headings.

Why the other options are wrong:

• How anaesthesia works - still a puzzle: While the puzzle of anaesthesia is mentioned, the paragraph specifically presents two opposing explanations - inhibiting vs. increasing receptor activity. The focus is on the conflict between theories, not the mystery itself. This is a partial truth trap.

Key Vocabulary:

• candidates = possible choices
• inhibited = reduced

General Tips:

• Read all headings first and underline key words before matching.
• Focus on the paragraph's main idea, not one interesting detail.
• Background paragraphs usually match simple, descriptive headings.
• If a paragraph talks about methods or measurement, avoid result headings.
• Matching Headings follow paragraph order, so work from top to bottom.