MCAT-TEST Real Exam Questions and Verified Answers

Question 1 Single choice

In the United States, breast cancer is the second leading cause of death for women, and as a result, the American Cancer Society, has recommended annual mammography screening for women age 40 years and older. It is estimated that the risk of mortality can be reduced through this procedure by approximately 20-25% during a ten-year period for women age 40 years and older.

In general, cancer screening behaviors have increased in the United States. According to the National Health Interview Survey, in 1987, approximately 29% of women age 40 years and older reported having had a mammogram in the last 2 years. By 2000, this increased to 70%. However, there are racial disparities, as fewer African American and Hispanic women have mammograms compared to their Caucasian female counterparts. Some studies have looked into these differences. Cultural factors seem to play a role in minority women obtaining fewer mammograms. Asian women, for example, do not like to discuss sensitive topics with strangers.

Prevention promotions have been designed to increase awareness for the need of breast cancer screening, particularly for women in racial and ethnic minority groups. An innovative breast cancer education program, called the Educational Intervention Asian Grocery Store-Based Education Program, was designed to target Asian women. Located in 20 different Asian grocery stores in communities, the cancer screening exhibits were placed at the entrances of the stores. As Asian women came into the grocery store, health information was passed out to Asian women. Even though only a small amount of women who were considered non-adherents to breast cancer screening ended up scheduling a screening, the study demonstrated an innovative culturally competent approach to health promotion.

Source: Adapted from G.R. Sadler, P.R. Beerman, K. Lee et al. "Promoting Breast Cancer Screening Among Asian American Women: The Asian Grocery Store Based Cancer Education Program." Copyright 2012 Journal of Cancer Education.

If the goal of the health communication is to influence individuals, families, neighborhoods, medical and social service organizations, and ultimately public health policy, health promoters are adhering to:

A
Urie Bronfenbrenner's ecological systems theory.
B
Murray Bowen's family systems theory.
C
John Bowlby's attachment theory.
D
Milton Gordon's assimilation theory.

Show answer and explanation

Correct answer: A

Explanation

A is correct. Ecological systems theory was first applied to understand child development and their socialization. It maintains that human behavior (in this case, health behavior) is influenced by multiple levels or spheres of influence of different orders, including the microsystem, which is related to the individual (e.g., the patient's beliefs, personality, past experiences, etc.); the mesosystem, which is related
to those with whom the person relates to directly (e.g., the family, community, neighborhood, workplace, school, friends, etc.); the exosystem, which relates to institutions and organizations which regulate that
person's community and with which the person does not often interact directly (e.g., health services, social services, legal institutions, industry, mass media, etc.); the macrosystem, which relates to that person's
cultural milieu (e.g., culture, traditions, laws, etc.); and the chronosystem, which relates to the dimension of time (e.g., when the person was born, when they lost their parents, etc.). The latter system was introduced a later stage of his career.
B. This is incorrect. Family systems theory argues that individual behaviors must be understood within the
family system they come about. That is, one cannot understand individuals outside their family unit. It does not identify a wider frame of influence, as ecological system theory does.
C. This is incorrect. Attachment theory emphasizes that behavior stem from the emotional attachments
developed between infant and parents/caregivers. There are several types of attachment, characterized by the different sets of behaviors and experiences, and that influence relationship patterns established during adulthood. This theory is not concerned with the spheres of social influence upon the individual, as ecological system theory is. D. This is incorrect. Assimilation theory is used in sociology to understand how immigrants adopt the cultural norms of the new host country. It is not concerned with the spheres of social influence upon the individual, as ecological system theory is.

Question 2 Single choice

The time has come to acknowledge the ascendancy of the humanistic psychology movement. The so-called "Third Stream" emerged at mid-century, asserting itself against the opposition of a pair of mighty, long-established currents, psychoanalysis and behaviorism. The hostility between these two older schools, as well as divisiveness within each of them, probably helped enable humanistic psychology to survive its early years. But the movement flourished because of its wealth of insights into the nature of this most inexact science.

Of the three major movements in the course of 20th century psychology, psychoanalysis is the oldest and most introspective. Conceived by Sigmund Freud as a means of treating mental and emotional disorders, psychoanalysis is based on the theory that people experience unresolved emotional conflicts in infancy and early childhood. Years later, although these experiences have largely disappeared from conscious awareness, they may continue to impair a person's ability to function in daily life. The patient experiences improvement when the psychoanalyst eventually unlocks these long-repressed memories of conflict and brings them to the patient's conscious awareness.

In the heyday of behaviorism, which occurred between the two world wars, the psychoanalytic movement was heavily criticized for being too concerned with inner subjective experience. Behavioral psychologists, dismissing ideas and feelings as unscientific, tried to deal only with observable and quantifiable facts. They perceived the human being merely as an organism which generated responses to stimuli produced by its
body and the environment around it. Patients' neuroses no longer needed analysis; they could instead by
modified by behavioral conditioning. Not even babies were safe: B.F. Skinner devised a container in which infants could be raised under "ideal" conditions -- if a sound-proof box can be considered the ideal environment for child-rearing.

By mid-century, a number of psychologists had grown dissatisfied with both the deterministic Freudian perspective and the mechanistic approach of behaviorism. They questioned the idea that human personality becomes permanently fixed in the first few years of life. They wondered if the purpose of psychology was really to reduce people to laboratory specimens. Was it not instead possible that human beings are greater than the sum of their parts? That psychology should speak to their search for fulfillment and meaning in life?

It is questions like these that members of the Third Stream have sought to address. While the movement cannot be simplified down to a single theoretical position, it does spring from certain fundamental propositions. Humanistic psychologists believe that conscious experience, rather than outward behavior, is the proper subject of psychology. We recognize that each human being is unique, capable of change and personal growth. We see maturity as a process dependent on the establishment of a set of values and the development of self. And we believe that the more aspects of self which are satisfactorily developed, the more positive the individual's self-image.

Abraham Maslow, a pioneer of the Third Stream, articulated a hierarchy of basic human needs, starting with food, water and air, progressing upward through shelter and security, social acceptance and belonging, to love, esteem and self-expression. Progress toward the higher stages cannot occur until all of the more basic needs have been satisfied. Individuals atop the pyramid, having developed their potential to the highest possible extent, are said to be "self-actualized".

If this humanist theoretical perspective is aimed at empowering the individual, so too are the movement's efforts in the practical realm of clinical psychology. Believing that traditional psychotherapists tend to lead patients toward predetermined resolutions of their problems, Carl Rogers pressed for objective evaluations of both the process and outcome of psychotherapeutic treatment. Not content to function simply as a reformer, Rogers also pioneered the development of "client-centered" or nondirective therapy, which emphasizes the autonomy of the client (i.e., patient). In client-centered therapy, clients choose the subjects for discussion, and are encouraged to create their own solutions to their problems.

The author states that "not even babies were safe" (line 35) most probably in order to:

A
emphasize that the use of even very young subjects is considered valid among most psychologists.
B
indicate the pervasive influence of behaviorists on the field of psychology.
C
show that behaviorists were anxious to apply their theories to a wide range of subjects.
D
warn of the dangers of psychoanalysis for children.

Show answer and explanation

Correct answer: C

Explanation

This asks why the author says that "not even babies were safe." The line reference in the question stem leads you to the last sentence of the third paragraph. You must read that sentence and a few of the neighboring sentences, to understand the context of the statement. Babies were not safe from the behaviorists. In the third sentence of paragraph 3, the author says that behaviorists saw humans merely as organisms producing responses to stimuli. The author goes on to say that, for behaviorists, the technique of stimulus-response or behavioral conditioning could be used to condition and cure neurotic patients, thereby avoiding the lengthy process of analysis. "Not even babies were safe," says the author and goes on to describe Skinner's attempt to condition babies. In other words, behaviorists believed that the benefits of their conditioning process were so universal that they tried to test it on, or impose it upon, everyone, even babies. So choice (C) is correct here: the author uses the quoted phrase to assert that behaviorists were eager to try out their conditioning theories on a wide variety of subjects. Choice (A) is wrong because it generalizes about what "most psychologists" consider valid. The author is talking specifically about behaviorists, not psychologists in general. There's no way of knowing whether "most psychologists" believe that using very young subjects is scientifically valid. Choice (B) is similarly misdirected. During its heyday, behaviorism probably did have a pervasive influence on the field of psychology. But this has nothing to do with the author's statement, which has more to do with the effect of behaviorism on babies than on the field of psychology.
Like choice (A), choice (D) is an incorrect and very broad generalization. Choice (D) suggests that the author is warning against the dangers of psychoanalysis for children. It is true that the author suggests he feels babies are endangered by the reasoning behind behaviorism. But, the author's statement really is about behaviorism in particular, not psychoanalysis in general.

Question 3 Single choice

Several techniques have been developed to determine the order of a reaction. The rate of a reaction cannot be predicted on the basis of the overall equation, but can be predicted on the basis of the rate-determining step. For instance, the following reaction can be broken down into three steps.

Step 1

(Slow)
Step 2

(fast)
Step 3

(fast)

Reaction 1
In this case, the first step in the reaction pathway is the rate-determining step. Therefore, the overall rate of the reaction must equal the rate of the first step, k1 [A] where k1 is the rate constant for the first step. (Rate constants of the different steps are denoted by kx, where x is the step number.)

In some cases, it is desirable to measure the rate of a reaction in relation to only one species. In a second-order reaction, for instance, a large excess of one species is included in the reaction vessel. Since a relatively small amount of this large concentration is reacted, we assume that the concentration essentially remains unchanged. Such a reaction is called a pseudo first-order reaction. A new rate constant, k', is established, equal to the product of the rate constant of the original reaction, k, and the concentration of the species in excess. This approach is often used to analyze enzyme activity.

In some cases, the reaction rate may be dependent on the concentration of a short-lived intermediate. This can happen if the rate-determining step is not the first step. In this case, the concentration of the intermediate must be derived from the equilibrium constant of the preceding step. For redox reactions, the equilibrium can be correlated with the voltage produced by two half-cells by means of the Nernst equation.
This equation states that at any given moment:

Equation 1
When

Reaction 2
Note: R = 8.314 J/K-mol; F = 9.6485 x 104 /mol.

) What is the effect of increasing the concentration of reactants in a voltaic cell?

A
The voltage increases, while the spontaneity of the reaction remains the same.
B
The spontaneity of the reaction increases, but the voltage remains the same.
C
Both the voltage and the spontaneity of the reaction increase.
D
The reaction rate increases, but the voltage and spontaneity of the reaction are unchanged.

Show answer and explanation

Correct answer: C

Explanation

To answer this question, you need to understand the relationship between the concentration of reactants and the spontaneity and voltage of the reaction. First let's review what is meant by voltage. When a reaction takes place in a voltaic cell, the oxidation reaction at the anode produces excess electrons.
Meanwhile, reduction at the cathode uses up electrons. For the reaction to continue, the cathode needs an additional supply of electrons. As a result of the two half-reactions, there is a movement of electrons through the wire from the anode to the cathode. The faster the reaction takes place, the greater the electrical force pushing electrons away from the anode and pulling them toward the cathode will be. This pressure on the electrons is called the electromotive force, or EMF. The electromotive force is measured in volts, and so is also known as the voltage. Don't confuse the voltage with the current--the voltage is the pressure on the electrons, while the current is the actual movement of electrons through the wire. The current depends not only on the pressure exerted by the EMF, but also on the amount of resistance of the wire. The voltage or electromotive force created by a redox reaction depends on the number of electrons exchanged in the reaction and the rate at which the reaction takes place. If the rate of the reaction changes, then the voltage or potential also changes. If the concentration of reactants is increased, then the reaction will move more quickly to the right, producing more electrons at the anode and using more at the cathode. This increases the voltage. So an increase in the concentration of reactants will increase the voltage. The spontaneity of a reaction is determined by Gibb's free energy, G. If G is negative, the reaction is spontaneous; if G is positive, the reaction is not spontaneous. There is a direct relationship between the
potential of a reaction and its free energy, given by the equation: G = -nFE, where n is the number of moles of electrons transferred in the reaction, F is Faraday's constant and E is the cell voltage. So what will happen to the value of G if we increase the concentration of the reactants? The reaction will proceed more quickly, increasing the flow of electrons, and therefore increasing the voltage, which in turn will make the value of G more negative. As the value of G becomes more negative, the reaction becomes more spontaneous. So choice C is correct; the increased concentration of reactants increases both the voltage
and the spontaneity of the reaction.

Question 4 Single choice

Fluoroscopy is an imaging technique that uses X-rays to obtain real-time moving images of the interior of the body. A patient was asked to perform cycles of deep inspiration and deep expiration. Fluoroscopy was used to measure the linear velocity of the movement of the diaphragm and the data was plotted against time. The origin in Figure 1 is the reference time 0 when the diaphragm was essentially in its equilibrium position.

At what time after t = 0 is the displacement of the diaphragm at a minimum?

A
A
B
B
C
C
D
D

Show answer and explanation

Correct answer: C

Explanation

To determine the displacement (NOT distance), take the area under the graph. The 2 similar sized trapezoids, one positive and the other negative, cancel each other. At time C, the diaphragm is back or near to its starting position; hence, its displacement has zero magnitude at that moment.

Question 5 Single choice

...Squeaking sand produces sounds with very high frequencies -- between 500 and 2,500 hertz, lasting less than a quarter of a second. The peals are musically pure, often containing four or five harmonic overtones. Booming sand makes louder, low-frequency sounds of 50 to 300 hertz, which may last as long as 15 minutes in larger dunes (although typically they last for seconds or less). In addition, they are rather noisy, containing a multitude of nearby frequencies. Booms have never been observed to contain more than one harmonic of the fundamental tone.
These dramatic differences once led to a consensus that although both types of sand produce acoustic emissions, the ways in which they do so must be substantially different.... In the late 1970s, however, Peter K. Haff, then at the California Institute of Technology, produced squeaks in booming sand, suggesting a closer connection between the two.
Both kinds of sand must be displaced to make sounds. Walking on some sand, for example, forces the sand underfoot to move down and out, producing squeaks. In the case of booming sand, displacement occurs during avalanches. It is within the avalanche that sound begins and where the answers must be hiding.
Before an avalanche can occur, winds must build a dune up to a certain angle, usually about 35 degrees for dry desert sand. Once an angle is achieved, the sand on the leeward side of the dune begins to slump.
Intact layers of sand slip over the layers below, like a sheared deck of cards. At the same time, the

individual grains in the upper layers tumble over the grains underneath, momentarily falling into the spaces between them and bouncing out again to continue their downward journey. Their concerted up-and-down motion is believed to be the secret source of sound. Fully developed avalanches, in which sliding plates of sand remain intact for most of their motion, have the greatest acoustic output. In some places, where large amounts of sand are involved, booming can be heard up to 10 kilometers away.
Because it is caused by large volumes of shearing sand, the roaring is also loud. In fact, sounds made by booming sand can be nearly deafening, and the vibrations causing them can be so intense that standing in their midst is nearly impossible.
A good place to start in exploring the vibrational properties of sand is with the grains themselves. The mean diameter of most sand grains, whether acoustically active or not, is about 300 microns. Usually the grains in a booming dune are very similar in size, especially near the leeward crest, where the sound most
often originates; such uniformity allows for more efficient shearing. Otherwise, the smaller grains impede
the smooth motion of the larger ones. Similar sizes do not alone allow sand to boom. On the contrary, the booming sands of Korizo and Gelf Kebib, also in Libya, feature an uncharacteristically broad range of particle sizes. Moreover, silent dune sand often contains grains somewhat similar to nearby booming sand.
Grains of booming sand also tend to have uncommonly smooth surfaces, with protrusions on the scale of
mere microns. Booming dunes are often found at the downwind end of large sand sources; having
bounced and rolled across the desert for long distances, the sand grains in these dunes are usually highly polished. Over time a grain can also be polished by repeated shifts within a moving dune. And squeaking sand as well tends to be exceptionally smooth.... ...Another important factor is humidity, because moisture can modify the friction between grains or cause sand to clump together, thus precluding shearing. Sounds occur in those parts of the dune that dry the fastest. Precipitation may be rare in the desert, but dunes retain water with remarkable efficiency. Sand near the surface dries quickly, however, and sand around a dune's crest tends to dry the fastest.

Which of the following characteristics is most helpful in differentiating booming sand from squeaking sand?

A
duration of the sound
B
frequency of the sound
C
size of the sand grains
D
smoothness of the sand grains

Show answer and explanation

Correct answer: B

Explanation

The first paragraph of the passage states that squeaking sand produces sounds with frequencies between 500 and 2500 hertz, while booming sand makes noises with frequencies from 50 to 300 hertz. This is the most definitive characteristic in distinguishing the two. None of the other choices allows for unambiguous categorization. Choice A, duration of sound, is not necessarily helpful since both kinds of sand can produce sounds lasting less than a second. Choice C, size of the sand grains, is also not useful: we are told in the passage that grains of booming sand tend to be of uniform size, but that there are exceptions.
Nothing is known about the actual (absolute) sizes of the grains, nor do we know anything about the size of grains of squeaking sand. Choice D, smoothness of grains, does not help in distinguishing the two since grains from both kinds of sand tend to be smooth.

Question 6 Single choice

X-rays are produced by a device which beams electrons with an energy between 103 and 106 eV at a metal plate. The electrons interact with the metal plate and are stopped by it. Much of the energy of the incoming electrons is released in the form of X-rays, which are high-energy photons of electromagnetic radiation. An example of such a device is shown below. Electrons are accelerated from the cathode towards the anode by an electric field.

There are two mechanisms by which the X-rays are produced within the metal. The first mechanism is called bremsstrahlung, which is German for "breaking radiation." X-rays are emitted by the electrons as they are brought to rest by interactions with the positive nuclei of the anode.

The second mechanism occurs when an incoming electron knocks an inner electron out of one of the metal atoms of the anode. This electron is replaced by an electron from a higher energy level of the atom, and a photon making up the energy difference is emitted.
X-rays are absorbed by a material when they pass through it. The amount of X-rays absorbed increases with the density of the material. In addition, lower energy X-rays are more likely to be absorbed than higher
energy X-rays. (Note: 1 eV = 1.6 x 1019 J; Planck's constant h = 4.1 x 10-15 eV-s; speed of light c = 3 x
108 m/s.)

What is the direction of the electric field that accelerates the electrons?

A
From the anode toward the cathode
B
From the cathode toward the anode
C
Into the page
D
Out of the page

Show answer and explanation

Correct answer: A

Explanation

This question involves the use of information in the passage along with some basic knowledge of electric fields and forces. In the second paragraph of the passage, we are told that electrons are accelerated from the cathode to the anode by an electric field. Now we have to figure out the direction of the electric field that would cause the electrons to move in that way. When the electric field lines are drawn, the arrows always point from the positive charge to the negative charge. So the direction of the electric field is the direction in which a positive charge would accelerate in that field. Since electrons are negative charges, they will be accelerated in the direction opposite to that of the electric field. We are pointing from the anode toward the cathode. Therefore, answer choice A is correct.

Question 7 Single choice

Hemoglobin (Hb) and myoglobin (Mb) are the O2-carrying proteins in vertebrates. Hb, which is contained within red blood cells, serves as the O2 carrier in blood and also plays a vital role in the transport of CO2 and H+. Vertebrate Hb consists of four polypeptides (subunits) each with a heme group. The four chains are held together by noncovalent attractions. The affinity of Hb for O2 varies between species and within species depending on such factors as blood pH, stage of development, and body size. For example, small mammals give up O2 more readily than large mammals because small mammals have a higher metabolic rate and require more O2 per gram of tissue.

The binding of O2 to Hb is also dependent on the cooperativity of the Hb subunits. That is, binding at one heme facilitates the binding of O2 at the other hemes within the Hb molecule by altering the conformation of the entire molecule. This conformational change makes subsequent binding of O2 more energetically favorable. Conversely, the unloading of O2 at one heme facilitates the unloading of O2 at the others by a similar mechanism.

Figure 1 depicts the O2-dissociation curves of Hb (Curves A, B, and C) and myoglobin (Curve D), where saturation, Y, is the fractional occupancy of the O2-binding sites. The fraction of O2 that is transferred from Hb as the blood passes through the tissue capillaries is called the utilization coefficient. A normal value is approximately 0.25.

Figure 1

Myoglobin facilitates transport in muscle and serves as a reserve store of O2. Mb is a single polypeptide chain containing a heme group, with a molecular weight of 18 kd. As can be seen in Figure 1, Mb (Curve
D. has a greater affinity for than Hb.

The llama is a warm-blooded mammal that lives in regions of unusually high altitudes, and has evolved a type of Hb that adapts it to such an existence.
If Curve B represents the O2-dissociation curve for horse Hb, which curve would most closely resemble the curve for llama Hb?

A
Curve A
B
Curve B
C
Curve C
D
Curve D

Show answer and explanation

Correct answer: A

Explanation

The key to answering this question lies in knowing that at high altitudes, atmospheric pressure is low, meaning that there is less oxygen in the air than at sea level. We're told that the llama has adapted to life at high altitudes by evolving a different type of hemoglobin. Since the partial pressure of oxygen is lower up in the mountains, llama hemoglobin must be able to bind oxygen MORE readily at low partial pressures of oxygen. And this means that for a given value of oxygen pressure on the X-axis of Figure 1, the llama's hemoglobin will be more saturated with oxygen than the horse's hemoglobin, since horses don't typically live in regions of unusually high altitude. In terms of Figure 1, this means that the llama oxygen-dissociation curve will be to the left of the horse's. So if Curve B is the horse curve, then the llama curve most closely resembles Curve A. Thus, choices B and C are wrong. As for Curve D; remember, we're told
in the passage that Curves A, B, and C are hemoglobin curves, while Curve D is the myoglobin curve. So, choice D is wrong.

Question 8 Single choice

Artificial kidneys have been used for almost 50 years to treat patients with different forms of renal failure.
The artificial kidney (dialysis machine) removes unwanted substances from the blood by diffusion. A patient's blood is passed through channels bounded by a porous, semi-permeable membrane that allows the free diffusion in both directions of all plasma constituents except the plasma proteins. Erythrocytes and

other cellular components of blood cannot pass through the membrane. The other side of the membrane is exposed to the dialyzing fluid which carries away the unwanted materials.
If the concentration of a material in the blood is greater than in the dialyzing fluid, there will be a net flow of the material from the plasma to the dialyzing fluid. If the concentration of a material in the blood is less than in the dialyzing fluid, there will be a net flow of the material from the dialyzing fluid into the blood. The composition of normal plasma, plasma in an individual suffering renal failure, and dialyzing fluid are shown in Table 1.

Table 1

Dialysis replaces some functions of the kidneys and attempts to correct the effects of renal failure. For example, patients with renal failure develop acidosis due to a buildup of metabolically produced acids in the circulation. Without dialysis, the pH of the blood will drop and coma may occur. Dialyzing fluid contains a relatively high concentration of bicarbonate which diffuses into the circulation and neutralizes the acid.

All of the following are removed from the plasma by dialysis EXCEPT:

A
Na+
B
K+
C
Urea
D
Glucose

Show answer and explanation

Correct answer: D

Explanation

By comparing the concentration of a material in the dialyzing fluid with the concentration in plasma, we can determine the net flow by passive diffusion through the semi-permeable membrane. Of all of the choices, only glucose has a higher concentration in the dialyzing fluid than in the plasma (with or without renal failure). Thus, glucose will not be removed from the plasma by dialysis. Choice A is incorrect because the concentration of Na+ in the dialyzing fluid is 133 mEq/L which is less than the concentration in plasma (142 mEq/L). Sodium will be removed.

Choice B is incorrect because the concentration of K+ (1.0 mEq/L) is much lower than the concentration in the plasma.
Choice C is incorrect because there is no urea in the dialyzing fluid. One of the primary functions of dialysis is the removal of urea from the circulation.

Question 9 Single choice

Aerobic respiration is the major process used by oxygen-requiring organisms to generate energy. During respiration, glucose is metabolized to generate chemical energy in the form of ATP:

The biochemical machinery necessary for cellular respiration is found in the mitochondria, small organelles scattered throughout the cytoplasm of most eukaryotic cells. The number of mitochondria per cell varies by tissue type and cell function.

Mitochondria are unusual in that they have their own genetic systems that are entirely separate from the cell's genetic material. However, mitochondrial replication is still dependent upon the cell's nuclear DNA to encode essential proteins required for replication. Despite this fact, mitochondria seem to replicate randomly, out of phase with both the cell cycle and other mitochondria.

The nature of the mitochondrial genome and proteinsynthesizing machinery has led many researchers to postulate that mitochondria may have arisen as the result of the ingestion of a bacterium by a primitive cell millions of years ago. It is postulated that the two may have entered into a symbiotic relationship and
eventually became dependent on each another; the cell sustained the bacterium, while the bacterium
provided energy for the cell. Gradually, the two evolved into the present-day eukaryotic cell, with the mitochondrion retaining some of its own DNA. This is known as the endosymbiotic hypothesis. Because

mitochondrial DNA is inherited in a non-Mendelian fashion (mitochondria are inherited from the maternal parent, who supplies most of the cytoplasm to the fertilized egg), it has been used to look at evolutionary
relationships among different organisms.

Four different human cell cultures -- erythrocytes, epidermal cells, skeletal muscle cells, and intestinal cells -- were grown in a medium containing radioactive adenine. After 10 days, the mitochondria were isolated via centrifugation, and their level of radioactivity was measured using a liquid scintillation counter.

Which of the following cells would be expected to have the greatest number of counts per minute of radioactive decay?

A
Erythrocytes
B
Epidermal cells
C
Skeletal muscle cells
D
Intestinal cells

Show answer and explanation

Correct answer: C

Explanation

According to the question stem, four different human cell cultures were grown in a medium containing radioactive adenine. So, the first thing that you should be thinking about is DNA replication; while these
cells are replicating they're going to incorporate this radioactive adenine into all of their DNA. This includes chromosomal DNA, as well as mitochondrial DNA. Mitochondria replicate independently of their cells.
Since all autosomal human cells have the same amount of DNA in their nuclei, the only difference in radioactivity will be the amount that was incorporated into the mitochondrial DNA. And this is why the cells' mitochondria were isolated via centrifugation, and then the radiation from each sample was measure using a scintillation counter. The cells with the greatest number of mitochondria will have the highest radioactive count when their mitochondria are separated. So, you need to determine which of the four cell types would have the greatest number of mitochondria. This number is dependent on the energy needs of the tissue.
Given the choices -- erythrocytes, epidermal cells, skeletal muscle cells, and intestinal cells -- you should know that the correct answer is choice C, skeletal muscle cells. Muscle cells need a lot of energy in order to contract. ATP is required every time a molecule of myosin binds to actin in the sarcomeres. In general, muscle cells have a higher content of mitochondria than do any other type of autosomal cell. Choice A, erythrocytes, do not even contain any mitochondria. Choice B, epidermal cells, do not have any special
energy requirements. The same thing applies to intestinal cells, choice D.

Question 10 Single choice

One of the most common methods that scientists use to determine the age of fossils is known as carbon dating. 14C is an unstable isotope of carbon that undergoes beta decay with a half-life of approximately 5,730 years. Beta decay occurs when a neutron in the nucleus decays to form a proton and an electron which is ejected from the nucleus. 14C is generated in the upper atmosphere when 14N, the most common isotope of nitrogen, is bombarded by neutrons. This mechanism yields a global production rate of 7.5 kg per year of 14C, which combines with oxygen in the atmosphere to produce carbon dioxide. Both the production and the decay of 14C occur simultaneously. This process continues for many half-lives of 14C, until the total amount of 14C approaches a constant. A fixed fraction of the carbon ingested by all living organisms will be 14C.
Therefore, as long as an organism is alive, the ratio of 14C to 12C that it contains is constant. After the organism dies, no new 14C is ingested, and the amount of 14C contained in the organism will decrease by beta decay. The amount of 14C that must have been present in the organism when it died can be calculated from the amount of 12C present in a fossil. By comparing the amount of 14C in the fossil to the calculated amount of 14C that was present in the organism when it died, the age of the fossil can be determined.

In generating 14C in the upper atmosphere, a 14C nucleus combines with a neutron to form a 14C nucleus and:

A
a proton.
B
an electron.
C
a 4He nucleus.
D
a neutron.

Show answer and explanation

Correct answer: A

Explanation

To answer this question, you have to balance a nuclear reaction. The question stem suggests the reaction, which has a nitrogen nucleus and a neutron on the left side and a carbon nucleus and the unknown particle on the right.

Two things must be balanced in a nuclear reaction: the charge of the nucleus (which corresponds to the number of protons), and the number of nucleons (which is the number of protons plus the number of neutrons). Balancing nuclear charge, we obtain 7 + 0 = 6 + b, which implies b = 1. Balancing the number of nucleons, we obtain 14 + 1 = 14 + a, which implies a = 1. Thus, the unknown particle is a nucleon with a charge of +1. The only particle that fits both criteria is the proton,
choice A.
Choice B is wrong because an electron is not a nucleon and it has a charge of ?.
Choice C is wrong because a helium nucleus has 4 nucleons and a charge of +2.
Choice D is wrong because a neutron has a charge of 0.