Chapter 2. Biology Strategy for the MCAT

2.1   SCIENCE SECTIONS OVERVIEW

There are three science sections on the MCAT:

•   Chemical and Physical Foundations of Biological Systems

•   Biological and Biochemical Foundations of Living Systems

•   Psychological, Social, and Biological Foundations of Behavior

The Chemical and Physical Foundations of Biological Systems section (Chem/Phys) is the third section on the test. It includes questions from General Chemistry (about 35%), Physics (about 25%), Organic Chemistry (about 15%), and Biochemistry (about 25%). Further, the questions often test chemical and physical concepts within a biological setting: for example, pressure and fluid flow in blood vessels. A solid grasp of math fundamentals is required (arithmetic, algebra, graphs, trigonometry, vectors, proportions, and logarithms); however, there are no calculus-based questions.

The Biological and Biochemical Foundations of Living Systems section (Bio/Biochem) is the first section on the test. Approximately 65% of the questions in this section come from biology, approximately 25% come from biochemistry, and approximately 10% come from Organic and General Chemistry. Math calculations are generally not required on this section of the test; however, a basic understanding of statistics as used in biological research is helpful.

The Psychological, Social, and Biological Foundations of Behavior section (Psych/Soc) is the fourth and final section on the test. About 60% of the questions will be drawn from Psychology, about 30% from Sociology, and about 10% from Biology. As with the Bio/Biochem section, calculations are generally not required, however a basic understanding of statistics as used in research is helpful.

Most of the questions in the science sections (about 75%) are passage-based, and each section will likely have about nine or ten passages. Passages consist of a few paragraphs of information and include equations, reactions, graphs, figures, tables, experiments, and data. Five to seven questions will be associated with each passage.

The remaining 25% of the questions in each science section are freestanding questions (FSQs). These questions appear in groups interspersed between the passages. Each group contains four to five questions.

95 minutes are allotted to each of the science sections. This breaks down to approximately one minute and 25 seconds per question.

2.2   GENERAL SCIENCE PASSAGE TYPES

The passages in the science sections fall into one of three main categories: Information and/or Situation Presentation, Experiment/Research Presentation, or Persuasive Reasoning.

Information and/or Situation Presentation

These passages either present straightforward scientific information or they describe a particular event or occurrence. Generally, questions associated with these passages test basic science facts or ask you to predict outcomes given new variables or new information. Here is an example of an Information/Situation Presentation passage:

Figure 1 shows a portion of the inner mechanism of a typical home smoke detector. It consists of a pair of capacitor plates which are charged by a 9-volt battery (not shown). The capacitor plates (electrodes) are connected to a sensor device, D; the resistor R denotes the internal resistance of the sensor. Normally, air acts as an insulator and no current would flow in the circuit shown. However, inside the smoke detector is a small sample of an artificially produced radioactive element, americium-241, which decays primarily by emitting alpha particles, with a half-life of approximately 430 years. The daughter nucleus of the decay has a half-life in excess of two million years and therefore poses virtually no biohazard.

Figure 1   Smoke detector mechanism

The decay products (alpha particles and gamma rays) from the ²⁴¹Am sample ionize air molecules between the plates and thus provide a conducting pathway which allows current to flow in the circuit shown in Figure 1. A steady-state current is quickly established and remains as long as the battery continues to maintain a 9-volt potential difference between its terminals. However, if smoke particles enter the space between the capacitor plates and thereby interrupt the flow, the current is reduced, and the sensor responds to this change by triggering

the alarm. (Furthermore, as the battery starts to “die out,” the resulting drop in current is also detected to alert the homeowner to replace the battery.)

C = ε₀ 

Equation 1

where ε₀ is the universal permittivity constant, equal to 8.85 × 10^-12 C²/(N·m²). Since the area A of each capacitor plate in the smoke detector is 20 cm² and the plates are separated by a distance d of 5 mm, the capacitance is 3.5 × 10^-12 F = 3.5 pF.

Experiment/Research Presentation

These passages present the details of experiments and research procedures. They often include data tables and graphs. Generally, questions associated with these passages ask you to interpret data, draw conclusions, and make inferences. Here is an example of an Experiment/Research Presentation passage:

The development of sexual characteristics depends upon various factors, the most important of which are hormonal control, environmental stimuli, and the genetic makeup of the individual. The hormones that contribute to the development include the steroid hormones estrogen, progesterone, and testosterone, as well as the pituitary hormones FSH (follicle-stimulating hormone) and LH (luteinizing hormone).

To study the mechanism by which estrogen exerts its effects, a researcher performed the following experiments using cell culture assays.

Experiment 1:

Human embryonic placental mesenchyme (HEPM) cells were grown for 48 hours in Dulbecco’s Modified Eagle Medium (DMEM), with media change every 12 hours. Upon confluent growth, cells were exposed to a 10 mg per mL solution of green fluorescent-labeled estrogen for 1 hour. Cells were rinsed with DMEM and observed under confocal fluorescent microscopy.

Experiment 2:

HEPM cells were grown to confluence as in Experiment 1. Cells were exposed to Pesticide A for 1 hour, followed by the 10 mg/mL solution of labeled estrogen, rinsed as in Experiment 1, and observed under confocal fluorescent microscopy.

Experiment 3:

Experiment 1 was repeated with Chinese Hamster Ovary (CHO) cells instead of HEPM cells.

Experiment 4:

CHO cells injected with cytoplasmic extracts of HEPM cells were grown to confluence, exposed to the 10 mg/mL solution of labeled estrogen for 1 hour, and observed under confocal fluorescent microscopy.

The results of these experiments are given in Table 1.

Table 1 Detection of Estrogen (+ indicates presence of Estrogen)

After observing the cells in each experiment, the researcher bathed the cells in a solution containing 10 mg per mL of a red fluorescent probe that binds specifically to the estrogen receptor only when its active site is occupied. After 1 hour, the cells were rinsed with DMEM and observed under confocal fluorescent microscopy. The results are presented in Table 2.

The researcher also repeated Experiment 2 using Pesticide B, an estrogen analog, instead of Pesticide A. Results from other researchers had shown that Pesticide B binds to the active site of the cytosolic estrogen receptor (with an affinity 10,000 times greater than that of estrogen) and causes increased transcription of mRNA.

Table 2 Observed Fluorescence and Estrogen Effects (G = green, R = red)

Based on these results, the researcher determined that estrogen had no effect when not bound to a cytosolic, estrogen-specific receptor.

Persuasive Reasoning

These passages typically present a scientific phenomenon along with a hypothesis that explains the phenomenon, and may include counter-arguments as well. Questions associated with these passages ask you to evaluate the hypothesis or arguments. Persuasive Reasoning passages in the science sections of the MCAT tend to be less common than Information Presentation or Experiment-based passages. Here is an example of a Persuasive Reasoning passage:

Two theoretical chemists attempted to explain the observed trends of acidity by applying two interpretations of molecular orbital theory. Consider the pK_a values of some common acids listed along with the conjugate base:

Recall that acids with a pK_a < 0 are called strong acids, and those with a pK_a > 0 are called weak acids. The arguments of the chemists are given below.

Chemist #1:

“The acidity of a compound is proportional to the polarization of the H—X bond, where X is some nonmetal element. Complex acids, such as H₂SO₄, HClO₄, and HNO₃ are strong acids because the H—O bonding electrons are strongly drawn towards the oxygen. It is generally true that a covalent bond weakens as its polarization increases. Therefore, one can conclude that the strength of an acid is proportional to the number of electronegative atoms in that acid.”

Chemist #2:

“The acidity of a compound is proportional to the number of stable resonance structures of that acid’s conjugate base. H₂SO₄, HClO₄, and HNO₃ are all strong acids because their respective conjugate bases exhibit a high degree of resonance stabilization.”

MAPPING A PASSAGE

“Mapping a passage” refers to the combination of on-screen highlighting and scratch paper notes that you take while working through a passage. Typically, good things to highlight include the overall topic of a paragraph, unfamiliar terms, unusual terms, numerical values, hypothesis, and results. Scratch paper notes can be used to summarize the paragraphs and to jot down important facts and connections that are made when reading the passage. Remember that highlighting disappears once you leave the passage, so a good set of scratch paper notes can be extremely useful if you have to return to the passage. More details on passage mapping will be presented in Section 2.5.

2.3   GENERAL SCIENCE QUESTION TYPES

Question in the science sections are generally one of three main types: Memory, Explicit, or Implicit.

Memory Questions

These questions can be answered directly from prior knowledge, with no need to reference the passage or question text. Memory questions represent approximately 25 percent of the science questions on the MCAT. Usually, Memory questions are found as FSQs, but they can also be tucked into a passage. Here’s an example of a Memory question:

Which of the following acetylating conditions will convert diethylamine into an amide at the fastest rate?

A)   Acetic acid / HCl

B)   Acetic anhydride

C)   Acetyl chloride

D)   Ethyl acetate

Explicit Questions

Explicit questions can be answered primarily with information from the passage, along with prior knowledge. They may require data retrieval, graph analysis, or making a simple connection. Explicit questions make up approximately 35−40 percent of the science questions on the MCAT; here’s an example (taken from the Information/Situation Presentation passage above):

The sensor device D shown in Figure 1 performs its function by acting as:

A)   an ohmmeter.

B)   a voltmeter.

C)   a potentiometer.

D)   an ammeter.

Implicit Questions

These questions require you to take information from the passage, combine it with your prior knowledge, apply it to a new situation, and come to some logical conclusion. They typically require more complex connections than do Explicit questions, and may also require data retrieval, graph analysis, etc. Implicit questions usually require a solid understanding of the passage information. They make up approximately 35−40 percent of the science questions on the MCAT; here’s an example (taken from the Experiment/Research Presentation passage above):

If Experiment 2 were repeated, but this time exposing the cells first to Pesticide A and then to Pesticide B before exposing them to the green fluorescent-labeled estrogen and the red fluorescent probe, which of the following statements will most likely be true?

A)   Pesticide A and Pesticide B bind to the same site on the estrogen receptor.

B)   Estrogen effects would be observed.

C)   Only green fluorescence would be observed.

D)   Both green and red fluorescence would be observed.

2.4   BIOLOGY ON THE MCAT

Biology is by far the most information-dense section on the MCAT. MCAT Biology topics span seven different semester-length courses (biochemistry, molecular biology, cell biology, microbiology, genetics, anatomy, and physiology). Further, the application of this material is potentially vast; passages can discuss anything from the details of some biochemical pathway to the complexities of genetic studies, to the nuances of an unusual disease. Fortunately, biology is the subject that MCAT students typically find the most interesting, and the one they have the most background in. People who want to go to medical school have an inherent interest in biology; thus this subject, although vast, seems more manageable than all the others on the MCAT.

The science sections of MCAT 2015 are likely to have around 9−10 passages and about 17 freestanding questions (FSQs). Biology and Biochemistry make up about 90% of the questions in the Biological and Biochemical Foundations of Living Systems section (Bio/Biochem). The remaining 10% are General and Organic Chemistry questions. Further, Biology questions can show up in the Psychological, Social, and Biological Foundations of Behavior section (about 10%) and in the Chemical and Physical Foundations of Biological Systems section. About 25% of that section is Biochemistry and frequently the passages and questions are biology-based.

2.5   TACKLING A BIOLOGY PASSAGE

Generally speaking, time is not an issue in the Bio/Biochem section of the MCAT. Because students have a stronger background in biology than in other subjects, the passages seem more understandable; in fact, readers sometimes find themselves getting caught up and interested in the passage. Often, students report having about 5 to 10 minutes “left over” after completing the section. This means that an additional minute or so can potentially be spent on each passage, thinking and understanding.

Passage Types as They Apply to Biology

Experiment/Research Presentation: Biology

This is the most common type of Biology passage. It typically presents the details behind an experiment along with data tables, graphs, and figures. Often these are the most difficult passages to deal with because they require an understanding of the reasoning behind the experiment, the logic to each step, and the ability to analyze the results and form conclusions. A basic understanding of biometry (basic statistics as they apply to biology and biology research) is necessary.

Information/Situation Presentation: Biology

This is the second most common type of Biology passage on the MCAT. These passages generally appear as one of two variants: either a basic concept with additional levels of detail included (for example, all the detail you ever wanted to know about the electron transport chain), or a novel concept with ties to basic information (for example, a rare demyelinating disease). Either way, Biology passages are notorious for testing concepts in unusual contexts. The key to dealing with these passages is to, first, not become anxious about all the stuff you might not know, and second, Figure out how the basics you do know apply to the new situation. For example, you might be presented with a passage that introduces hormones you never heard of, or novel drugs to combat diseases you didn’t know existed. First, don’t panic. Second, look for how these new things fit into familiar categories: for example, “peptide vs. steroid,” or “sympathetic antagonist.” Then answer the questions with these basics in mind.

That said, you have to know your basics. This will increase your confidence in answering freestanding questions, as well as increase the speed with which to find the information in the passage. The astute MCAT student will never waste time staring at a question thinking, “Should I know this?” Instead, because she has a solid understanding of the necessary core knowledge, she’ll say, “No, I am NOT expected to know this, and I am going to look for it in the passage.”

Persuasive Reasoning: Biology

This is the least common passage type in Biology. It typically describes some biological phenomenon, and then offers one or more theories to explain it. Questions in Persuasive Reasoning passages ask you to determine support for one of the theories, or present new evidence and ask which theory is now contradicted.

One last thought about Biology passages in general: Because the array of topics is so vast, Biology passages often pull questions from multiple areas of biology into a single, general topic. Consider, for example, a passage on renal function. Question topics could include basics about the kidney, transmembrane transport, autonomic control, blood pressure, hormones, biochemical energy needs, or a genetics question about a rare kidney disease.

READING A BIOLOGY PASSAGE

Although tempting, try not to get bogged down reading all the little details in a passage. Again, because most premeds have an inherent interest in biology and the mechanisms behind disease, it’s very easy to get lost in the science behind the passages. In spite of having that “extra” time, you don’t want to use it all up reading what isn’t necessary. Each passage type requires a slightly different style of reading.

Information/Situation Presentation passages require the least reading. These should be skimmed to get an idea of the location of information within the passage. These passages include a fair amount of detail that you might not need, so save the reading of these details until a question comes up about them. Then go back and read for the finer nuances.

Experiment/Research Presentation passages require the most reading. You are practically guaranteed to get questions that ask you about the details of the experiment, why a particular step was carried out, why the results are what they are, how to interpret the data, or how the results might change if a particular variable is altered. It’s worth spending a little more time reading to understand the experiment. However, because there will be a fair number of questions unrelated to the experiment, you might consider answering these first, then going back for the experiment details.

Persuasive Argument passages are somewhere in the middle. You can skim them for location of information, but you also want to spend a little time reading the details of and thinking about the arguments presented. It is extremely likely that you will be asked a question about them.

Advanced Reading Skills

To improve your ability to read and glean information from a passage, you need to practice. Be critical when you read the content; watch for vague areas or holes in the passage that aren’t explained clearly. Remember that information about new topics will be woven throughout the passage; you may need to piece together information from several paragraphs and a Figure to get the whole picture.

After you’ve read, highlighted, and mapped a passage (more on this in a bit) stop and ask yourself the following questions:

•   What was this passage about? What was the conclusion or main point?

•   Was there a paragraph that was mostly background?

•   Were there paragraphs or figures that seemed useless?

•   What information was found in each paragraph? Why was that paragraph there?

•   Are there any holes in the story?

•   What extra information could I have pulled out of the passage? What inferences or conclusions could I make?

•   If something unique was explained or mentioned, what might be its purpose?

•   What am I not being told?

•   Can I summarize the purpose and/or results of the experiment in a few sentences?

•   Were there any comparisons in the passage?

This takes a while at first, but eventually becomes second nature and you will start doing it as you are reading the passage. If you have a study group you are working with, consider doing this as an exercise with your study partners. Take turns asking and answering the questions above. Having to explain something to someone else so not only solidifies your own knowledge, but helps you see where you might be weak.

MAPPING A BIOLOGY PASSAGE

Mapping a Biology passage is a combination of highlighting and scratch paper notes that can help you organize and understand the passage information.

Resist the temptation to highlight everything! (Everyone has done this: You’re reading a biology textbook with a highlighter, and then look back and realize that the whole page is yellow!) Restrict your highlighting to a few things:

•   The main theme of a paragraph

•   An unusual or unfamiliar term that is defined specifically for that passage (e.g., something that is italicized)

•   Statements that either support the main theme or contradict the main theme

•   List topics: sometimes lists appear in paragraph form within a passage. Highlight the general topic of the list.

Scratch paper should be organized. Make sure the passage number appears at the top of your scratch paper notes. For each paragraph, note “P1,” “P2,” etc., on the scratch paper, and jot down a few notes about that paragraph. Try to translate biology jargon into your own words using everyday language (this is particularly useful for experiments). Also, make sure to note down simple relationships (e.g., the relationship between two variables).

Pay attention to equations, figures, and the like to see what type of information they deal with. Don’t spend a lot of time analyzing at this point, but do jot down on your scratch paper “Fig 1” and a brief summary of the data. Also, if you’ve discovered a list in the passage, note its topic and location down on your scratch paper.

Let’s take a look at how we might highlight and map a passage. Below is a passage on eye physiology.

The wall of the human eye is composed of three layers of tissue, an outer layer of tough connective tissue, a middle layer of darkly pigmented vascular tissue, and an inner layer of neural tissue. The outer layer is subdivided into the sclera, the white portion, and the cornea, the clear portion. The inner layer is more commonly known as the retina and contains several types of cells.

Figure 1   Retina Structure

The photoreceptors of the retina include rods and cones which respond to light under different circumstances. Rods are more sensitive to light but cannot distinguish color; cones are less sensitive to light overall, but can respond to different wavelengths. Response to light involves visual pigments, which in all cases consist of a light-absorbing molecule called retinal (derived from vitamin A) bound to a protein called opsin. The type of opsin in the visual pigment determines the wavelength specificity of the retinal. The specific visual pigment in rod cells is called rhodopsin.

Figure 2   The Two Forms of Retinal

In the absence of light, Na⁺ channels in the membranes of rod cells are kept open by cGMP. The conformational change in retinal upon light absorption causes changes in opsin as well; this triggers a pathway by which phosphodiesterase (PDE) is activated. Active PDE converts cGMP to GMP, causing it to dissociate from the Na⁺ channel and the channel to close. Until retinal regains its bent shape (helped by enzymes), the rod is unable to respond further to light.

Figure 3   Rod Cell in Darkness

Visual defects can be caused by abnormal visual pigments or by misshapen eyeballs; for example, myopia (nearsightedness) is due to an eyeball that is too long, causing light rays from distant objects to focus in front of the retina so the image appears blurry.

Analysis and Passage Map

This passage is an Information Presentation passage and starts out with a paragraph about the structure of the eye and its layers. This is primarily a background paragraph and can be skimmed quickly, with a few words highlighted. Figure 1 shows the detail of the retina.

The second paragraph goes into more detail about the photoreceptors, and specifically compares the functions of rods and cones. There are few more italicized terms; this paragraph is presenting information that is beyond what you are expected to know about the eye for the MCAT. Figure 2 shows the conversion between the two forms of retinal.

The third paragraph presents details about rod cells, and in particular points out a unique feature of rod cells: that their Na⁺ channels are typically open in light. On stimulation by light, they close. This is unusual behavior in the nervous system, since it is the opposite of what typically occurs. Figure 3 confirms this, as the cell in darkness appears to be resting at −40 mV, 30 mV more positive than typical neurons rest at.

The final paragraph is a brief description of visual defects. Like paragraph 1, it only needs to be skimmed briefly. Here’s what your passage map might look like:

P1 – 3 layers of eyeball, Fig 1 retina detail

P2 – photoreceptors

rods no color, more sensitive

cones less sensitive, respond to different colors

details on vis pigments. Fig 2 convert retinal

P3 – rod function. WEIRD Na+ channels open in dark, close in light.

depol in light, hyperpol in dark

P4 – visual defects

Let’s take a look at a different passage. Below is an Experiment/Research Presentation passage.

The development of sexual characteristics depends upon various factors, the most important of which are hormonal control, environmental stimuli, and the genetic makeup of the individual. The hormones that contribute to the development include the steroid hormones estrogen, progesterone, and testosterone, as well as the pituitary hormones FSH (follicle-stimulating hormone) and LH (luteinizing hormone).

To study the mechanism by which estrogen exerts its effects, a researcher performed the following experiments using cell culture assays.

Experiment 1:

Human embryonic placental mesenchyme (HEPM) cells were grown for 48 hours in Dulbecco’s Modified Eagle Medium (DMEM), with media change every 12 hours. Upon confluent growth, cells were exposed to a 10 mg per mL solution of green fluorescent-labeled estrogen for 1 hour. Cells were rinsed with DMEM and observed under confocal fluorescent microscopy.

Experiment 2:

HEPM cells were grown to confluence as in Experiment 1. Cells were exposed to Pesticide A for 1 hour, followed by the 10 mg/mL solution of labeled estrogen, rinsed as in Experiment 1, and observed under confocal fluorescent microscopy.

Experiment 3:

Experiment 1 was repeated with Chinese Hamster Ovary (CHO) cells instead of HEPM cells.

Experiment 4:

CHO cells injected with cytoplasmic extracts of HEPM cells were grown to confluence, exposed to the 10 mg/mL solution of labeled estrogen for 1 hour, and observed under confocal fluorescent microscopy.

The results of these experiments are given in Table 1.

Table 1 Detection of Estrogen (+ indicates presence of estrogen)

After observing the cells in each experiment, the researcher bathed the cells in a solution containing 10 mg/mL of a red fluorescent probe that binds specifically to the estrogen receptor only when its active site is occupied. After 1 hour, the cells were rinsed with DMEM and observed under confocal fluorescent microscopy. The results are presented in Table 2.

The researcher also repeated Experiment 2 using Pesticide B, an estrogen analog, instead of Pesticide A. Results from other researchers had shown that Pesticide B binds to the active site of the cytosolic estrogen receptor (with an affinity 10,000 times greater than that of estrogen) and causes increased transcription of mRNA.

Table 2 Observed Fluorescence and Estrogen Effects (G = green, R = red)

Based on these results, the researcher determined that estrogen had no effect when not bound to a cytosolic, estrogen-specific receptor.

Analysis and Passage Map

This passage starts out with a very general background paragraph. Not much to do here, but it does tell us that estrogen is going to be the hormone of focus.

The next few paragraphs are short descriptions of four different experiments. These should be read to understand not only what’s happening in each experiment but also what the differences in the experiments are. Note this on your scratch paper.

Table 1 shows the results of the four experiments. It should jump out at you that estrogen is found everywhere; in other words, it is not restricted from any area of the cell.

After Table 1, the passage describes two modifications to the experiments. As with the original experiments, it’s worth taking a little time to read and understand what’s going on. The first big difference is that the researchers aren’t just looking for the presence of estrogen, but also want to know when it’s bound to its receptor. The second big difference is the testing of an estrogen analog, Pesticide B.

Table 2 shows the results of when estrogen is bound and when it isn’t. These results could be combined with the experiment description results on your map:

P1 – hormones that contribute to development, estrogen

E1 – HEPM cells exposed to estrogen, green + red = estrogen effects

E2 – Pesticide A, green only, must inhibit binding of estrogen to recept.

E3 – CHO cells, green only, no recept.

E4 – CHO cells + HEPM cytoplasm, green + red, recept is in cytoplasm

Table 1 – estrogen is not restricted from anywhere in the cell

Further exp’ts – red probe for bound active site, and Pesticide B (estrogen analog w/higher affinity)

One last thought about passages: remember that, as with all sections on the MCAT, you can do the passages in the order you want to. There are no extra points for taking the test in order. Generally, passages will fall into one of four main subject groups:

•   Biochemistry

•   Other non-physiology

•   Physiology

•   Organic/general chemistry

Figure out which group you are most comforTable with, and do those passages first.

2.6   TACKLING THE QUESTIONS

Questions in the Biology section mimic the three typical questions of the science sections in general: Memory, Explicit, and Implicit.

Question Types as They Apply to Biology

Biology Memory Questions

Memory questions are exactly what they sound like: They test your knowledge of some specific fact or concept. While Memory questions are typically found as freestanding questions, they can also be tucked into a passage. These questions, aside from requiring memorization, do not generally cause problems for students because they are similar to the types of questions that appear on a typical college biology exam. Below is an example of a freestanding Memory question:

Regarding embryogenesis, which of the following sequence of events is in correct order?

A)   Implantation—cleavage—gastrulation—neurulation—blastulation

B)   Blastulation—implantation—cleavage—neurulation—gastrulation

C)   Implantation—blastulation—gastrulation—cleavage—neurulation

D)   Cleavage—blastulation—implantation—gastrulation—neurulation

The correct answer to the question above is choice D. Here’s another example. This question is from a passage:

The genital organs of the guevedoche that develop at puberty are derivatives of the mesodermal germ layer. Which of the following is/are also derivatives of the mesodermal germ layer?

  I.  Skeletal muscle

 II.  Liver

III.  Kidney

A)   I only

B)   II only

C)   I and III only

D)   II and III only

Note that this question includes an additional, unnecessary sentence at the beginning, but it is a Memory question all the same. You don’t need to know anything about the guevedoche to answer the question, and the information in that first sentence does not help you in any way. The correct answer to the question above is choice C.

There is no specific “trick” to answering Memory questions; either you know the answer or you don’t.

It’s usually a good idea to tackle all freestanding questions in the section first, since they are typically Memory questions and don’t require a lot of thought or analysis.

If you find that you are missing a fair number of Memory questions, it is a sure sign that you don’t know the content well enough. Go back and review.

Biology Explicit Questions

True, pure Explicit questions are rare in the Biology section. A purely Explicit question can be answered only with information in the passage. Below is an example of a pure Explicit question taken from the eye passage above:

The middle layer of the eyeball wall most likely contains:

A)   bipolar cells.

B)   photoreceptors.

C)   blood vessels.

D)   collagen fibers.

Referring back to the map for this passage, it indicates that information about the layers of the eyeball are in paragraph 1. It states that the middle layer is a “darkly pigmented vascular layer,” meaning that it contains blood vessels. The correct answer is C.

However, more often in the biology section, Explicit questions are more of a blend of Explicit and Memory; they require not only retrieval of passage information, but also recall of some relevant fact. They usually do not require a lot of analysis or connections. Here’s an example of the more common type of Explicit question:

Pesticide A most likely functions as:

A)   an agonist.

B)   an inhibitor.

C)   a lipase.

D)   a receptor.

To answer this question, you first need to retrieve information from the passage about the effects of Pesticide A. From Table 2 we know that it prevents estrogen from binding to its receptor (and we noted this on our passage map). You also need to remember the definitions of the terms in the answer choices (agonists cause similar effects, inhibitors prevent effects, lipases break down lipids, and receptors bind ligands to cause effects). Based on our known definitions, choices A and D can be eliminated, and while Pesticide A could be functioning as a lipase that breaks down estrogen, “inhibitor” is a more accurate term (choice B is better than choice C and is the correct answer).

A final subgroup in the Explicit question category are graph interpretation questions. These fall into one of two types; one, those that ask you to take graphical information from the passage and convert it to a text answer, or those that take text from the passage and ask you to convert it to a graph. On the following page is an example of the latter type:

Which of the following graphs would best illustrate the binding of estrogen (E) to its receptor in the presence of its analog, Pesticide B?

A)   

B)   

C)   

D)   

From our passage map, we know that information about Pesticide B is found near the end of the passage, where it describes “further experiments.” The passage states that Pesticide B functions as an estrogen analog that binds to the estrogen receptor with a much higher affinity than does estrogen. In other words, if Pesticide B is around, the receptor will preferentially bind it, and not estrogen. So as the concentration of Pesticide B rises, the amount of estrogen bound to the receptor should fall. This is shown in choice B.

If you find that you are missing Explicit questions, practice your passage mapping. Make sure you aren’t missing the critical items in the passage that lead you to the right answer. Slow down a little; take an extra 15 to 30 seconds per passage to read or think about it more carefully.

Biology Implicit Questions

Implicit questions require the most thought. These require recall not only of biology information but also information gleaned from the passage, and a more in-depth analysis of how the two relate. Implicit questions require more analysis and connections to be made than Explicit questions. Often they take the form “If … then.…” Below is an example of a classic Implicit question, taken from the Experiment passage shown above.

If Experiment 2 were repeated, but this time exposing the cells first to Pesticide A and then to Pesticide B before exposing them to the green fluorescent-labeled estrogen and the red fluorescent probe, which of the following statements will most likely be true?

A)   Pesticide A and Pesticide B bind to the same site on the estrogen receptor.

B)   Estrogen effects would be observed.

C)   Only green fluorescence would be observed.

D)   Both green and red fluorescence would be observed.

To answer this question, conclusions have to be drawn from the experiments described in the passage, and new conclusions have to be predicted based on the new circumstance. Many many more connections need to be made than when answering an Explicit question. From the passage, we need to Figure out that Pesticide A is an inhibitor. We also have to Figure out that it does not bind at the active site of the receptor (data from Table 2). We have to know what green fluorescence and red fluorescence imply. We have to draw on the information provided about Pesticide B to know that it is an analog and that it binds to the active site of the estrogen receptor. We have to combine all of this together and come to a logical conclusion: Since Pesticide A is an inhibitor, it would prevent the binding of Pesticide B and thus prevent estrogen effects (choice B can be eliminated). If Pesticide B cannot bind, we would only see green fluorescence (choice D can be eliminated and choice C is probably correct). Since Pesticide A by itself does not produce red fluorescence, it must not be binding at the active site, which is where Pesticide B binds, (choice A can be eliminated and choice C is definitely correct).

Here’s another example of an Implicit question, drawn from the same passage:

When the researcher performed Experiment 2 using Pesticide B instead of Pesticide A, which of the following fluorescence and estrogen effects did the researcher most likely observe?

A)   Media: green and red

Cytoplasm: green and red

Nucleus: green and red

Estrogen effects: no

B)   Media: green only

Cytoplasm: green and red

Nucleus: green and red

Estrogen effects: no

C)   Media: green only

Cytoplasm: green and red

Nucleus: green and red

Estrogen effects: yes

D)   Media: green only

Cytoplasm: green and red

Nucleus: green only

Estrogen effects: no

To answer this question we again must combine passage information with logical inference and working memory. Since red fluorescence indicates binding of the receptor, and since the receptor is never in the media, there can never be red fluorescence in the media (choice A can be eliminated). We know from the passage that Pesticide B binds at the active site of the receptor, and we know that the receptor is found in the cytoplasm. We also know from the passage that Pesticide B causes increased mRNA transcription, and we know from memory that to induce mRNA transcription, the receptor must move into the nucleus. Thus, red fluorescence must be observed in the nucleus as well (choice D can be eliminated). Since Pesticide B is defined as an “estrogen analog,” and since we know from memory that analogs cause similar effects, it is likely that estrogen effects will be observed. The fact that increased mRNA transcription occurs supports this idea (choice B can be eliminated and choice C is correct). Again, many more connections need to be made to answer Implicit question; process of elimination is typically the best approach.

If you find that you are missing a lot of Implicit questions, make sure first of all that you are using POE aggressively. Second, go back and review the explanations for the correct answer, and Figure out where your logic went awry. Did you miss an important fact in the passage? Did you forget the relevant Biology content? Did you follow the logical train of thought to the right answer? Once you Figure out where you made your mistake, you will know how to correct it.

2.7   SUMMARY OF THE APPROACH TO BIOLOGY

How to Map the Passage and Use Scratch Paper

1)   The passage should not be read like textbook material, with the intent of learning something from every sentence (science majors especially will be tempted to read this way). Passages should be read to get a feel for the type of questions that will follow, and to get a general idea of the location of information within the passage.

2)   Highlighting—Use this tool sparingly, or you will end up with a passage that is completely covered in yellow highlighter! Keep in mind that highlighting does not persist as you move from passage to passage within the section. If you want to make more permanent notes, use the scratch paper. Highlighting in a Biology passage should be used to draw attention to a few words that demonstrate one of the following:

•   The main theme of a paragraph

•   An unusual or unfamiliar term that is defined specifically for that passage (e.g., something that is italicized)

•   Statements that either support the main theme or counteract the main theme

•   List topics (see below)

3)   Pay brief attention to equations, figures, and experiments, noting only what information they deal with. Do not spend a lot of time analyzing at this point.

4)   For each paragraph, note “P1,” “P2,” etc. on the scratch paper and jot down a few notes about that paragraph. Try to translate biology-speak into your own words using everyday language. Especially note down simple relationships (e.g., the relationship between two variables).

5)   Lists—Whenever a list appears in paragraph form, jot down on the scratch paper the paragraph and the general topic of the list. It will make returning to the passage more efficient and help to organize your thoughts.

6)   Scratch paper is only useful if it is kept organized! Make sure that your notes for each passage are clearly delineated and marked with the passage number. This will allow you to easily read your notes when you come back to a review a marked question. Resist the temptation to write in the first available blank space as this makes it much more difficult to refer back to your work.

Biology Question Strategies

1)   Remember that the content in Biology is vast, so don’t panic if something seems completely unfamiliar. Understand the basic content well, find the basics in the unfamiliar topic, and apply them to the question.

2)   Process of Elimination is paramount! The strikeout tool allows you to eliminate answer choices; this will improve your chances of guessing the correct answer if you are unable to narrow it down to one choice.

3)   Answer the straightforward questions first (typically the freestanding questions or the memory questions). Leave questions that require analysis of experiments and graphs for later. Take the test in the order YOU want.

4)   Make sure that the answer you choose actually answers the question, and isn’t just a true statement.

5)   Try to avoid answer choices with extreme words such as “always,” “never,” etc. In biology, there is almost always an exception and answers are rarely black-and-white.

6)   I-II-III questions: always work between the I-II-III statements and the answer choices. Unfortunately, it is not possible to strike out the Roman numerals, but this is a great use for scratch paper notes. Once a statement is determined to be true (or false) strike out answer choices which do not contain (or do contain) that statement.

7)   LEAST/EXCEPT/NOT questions: Don’t get tricked by these questions that ask you to pick that answer that doesn’t fit (the incorrect or false statement). It’s often good to use your scratch paper and write a T or F next to answer choices A–D. The one that stands out as different is the correct answer!

8)   Again, don’t leave any question blank.

A Note About Flashcards

Contrary to popular belief, flashcards are NOT the best way to study for the MCAT. For most of the exams you’ve taken previously, flashcards were probably helpful. This was because those exams mostly required you to regurgitate information, and flashcards are pretty good at helping you memorize facts. Remember, however, that the most challenging aspect of the MCAT is not that it requires you to memorize the fine details of content-knowledge, but that it requires you to apply your basic scientific knowledge to unfamiliar situations. Flashcards won’t help you do that.

There is only one situation in which flashcards can be beneficial, and that’s if your basic content knowledge is deficient in some area. For example, if you don’t know the hormones and their effects in the body, flashcards can help you memorize these facts. Or, maybe you are unsure of the functions of the different brain regions. You might find that flashcards can help you memorize these. (And remember that part of what makes flashcards useful is the fact that you make them yourself. Not only are they then customized for your personal areas of weakness, the very act of writing information down on a flashcard helps stick that information in your brain.) But other than straight, basic fact-memorization in your personal weak areas, you are better off doing and analyzing practice passages than carrying around a stack of flashcards.