MCAT Biology : Biology

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Biology

To form a female zygote, the sperm cell must contribute which chromosome(s)?

Possible Answers:

A Y-chromosome

Two Y-chromosomes

Two X-chromosomes

Both an X- and a Y-chromosome

An X-chromosome

Correct answer:

An X-chromosome

Explanation:

The necessary genotype for a female zygote is XX.

The mother will share this XX genotype (since she is also female) and will contribute one X-chromosome. The father, however, will be male and have the genotype XY. This means he has a 50% chance of passing on an X-chromosome and a 50% chance of passing on a Y-chromosome. If the zygote inherits a Y-chromosome from the father's sperm, then the offspring will be male. If the zygote inherits an X-chromosome from the father's sperm, then the resulting genotype will be XX and the offspring will be female.

Example Question #1 : Reproductive System And Development

What is a totipotent cell?

Possible Answers:

Stem cells from the inner cell mass

A cell that has the ability to differentiate into a limited number of tissue types if exposed to the appropriate chemical signals

A cell that has the ability to differentiate into any type of tissue if exposed to the appropriate chemical signals

A cell that has the ability to form a complete organism through embryogenesis

Stem cells from adult tissues

Correct answer:

A cell that has the ability to form a complete organism through embryogenesis

Explanation:

Totipotent cells have the ability to propogate and differentiate into any cell types, including the trophoblast. They are different from stem cells, which could be considered multipotent (able to differentiate into multiple tissue types) or pleuripotent (able to differentiate into any major tissue type, but cannot create trophoblast). The only truly totipotent cells are the first two blastomeres.

Example Question #1 : Systems Biology And Tissue Types

What is the "common dogma"?

Possible Answers:

Cells lose genetic material over time, becoming less totipotent

All cells come from other cells

None of the other answers

Most cells in the body contain a complete genome, despite the fact that most of the genes in the genome are not necessary for each cell's specific function

All organisms are made of cells

Correct answer:

Most cells in the body contain a complete genome, despite the fact that most of the genes in the genome are not necessary for each cell's specific function

Explanation:

Most cells contain a complete genome, but not all genes are activated in each cell. Activation of particular genes produces appropriate protein function.

Example Question #1 : Reproductive System And Development

Differentiation of the endoderm in a developing human embryo will eventually give the human the ability to __________.

Possible Answers:

breathe

think

move

produce urine

circulate blood

Correct answer:

breathe

Explanation:

The endoderm develops into a number of internal organs, including the lung, which are vital for breathing.

The kidneys (urine production), muscles (movement), and blood vessels (blood circulation) develop from the mesoderm. The brain (thought) develops from the ectoderm.

Example Question #1 : Biology

A new medication has been created that is very effective at treating brain tumors; however, the medication has a short half-life once inside the body. If the medication travels through the blood stream, which method of administration would give the medication the most time to affect a tumor in the brain? (Assume an equal dosage of the medicine is used for each potential method.)

Possible Answers:

Inhalation

Sublingual

Subcutaneous Injection

Intravenous Injection (Jugular Vein)

Correct answer:

Inhalation

Explanation:

This question is targeting your knowledge of the circulatory system. Since the medication has a short half-life, it is necessary that it be carried by the patient's blood stream to the tumor as quickly as possible. Blood travels through the right side of the heart, to the lungs, through the left side of the heart, then to the body. Therefore, inhalation of a chemical would require the least amount of traveling (Lungs, Left Atrium, Left Ventricle, Body). Each other method of administration, including IV, would require more time to travel to the brain. For example, for the IV answer choice, the pathway would be Vein, Right Atrium, Right Ventricle, Lungs, Left Atrium, Left Ventricle, Body.

Example Question #1 : Other Concepts

Thermoregulation of the human body is controlled by a __________.

Possible Answers:

set of hormones

None of these answers

biological rhythm

positive feedback mechanism

negative feedback mechanism

Correct answer:

negative feedback mechanism

Explanation:

Like many biological functions, thermoregulation is controlled by a negative feedback system. This is because the response is the opposite of the input: a hot environment triggers cooling, while a cool environment triggers heating. A positive feedback system would intensify a response in the same direction as the input. If a positive feedback mechanisms were true of regulating body temperature, cold weather would trigger sweating and dilation of blood vessels. The result would be that you would get even more cold, which would not be good for maintaining homeostasis. Hormones do help regulate many body functions, but they are not the best description of how body temperature is controlled.

Example Question #2 : Other Concepts

Which of the following accurately describes the body of a fresh water fish immediately following its transfer to a salt-water aquarium?

Possible Answers:

Isotonic

Hypotonic

Hypertonic

Hyperosmotic

Correct answer:

Hypotonic

Explanation:

In its home environment, the fresh water fish will be in equilibrium with its surroundings. As such, it will essentially be isotonic with a fresh water solution. This represents a relatively low solute concentration in the fish's body.

When we transfer this fish to a medium that is more densely concentrated with solute molecules, the fresh-water fish will be hypotonic in relation to the external medium. The salt in the surrounding water will cause the external environment to be more concentrated than the body of the fish. As a result, the fish will quickly become dehydrated as water exits its body.

Hypertonic and hyperosmotic are synonyms, which both refer to greater concentrations than the surroundings (opposite the scenario described).

Example Question #2 : Other Concepts

A container has a semi-permeable membrane separating equal volumes of equimolar aqueous glucose and sodium hydroxide solutions. Which of the following describes the heights of the solutions after the system has equilibrated?

Possible Answers:

The sodium hydroxide solution will be at a higher level

The two solutions will be at the same height

The glucose solution will be at a higher level

We must know the shape of the container to determine an answer

Correct answer:

The sodium hydroxide solution will be at a higher level

Explanation:

Answering this question depends on your knowledge of concentration gradients and solution chemistry. Even though the sodium hydroxide and glucose solutions are equimolar, sodium hydroxide is an electrolyte, meaning it dissociates when in solution. The solute content of the sodium hydroxide solution is actually twice that of the glucose solution due to the presence of ions. This means that the sodium hydroxide solution will actually be hypertonic with respect to the glucose solution.

Only water can cross the semi-permeable membrane; the ions will be trapped in their respective chambers. Water from the glucose solution will diffuse down its concentration gradient into the sodium hydroxide solution. After the system equilibrates, the water level in the sodium hydroxide solution will be higher.

Example Question #1 : Biology

The cell is the most basic functional unit of life.  Everything that we consider to be living is made up of cells, and while there are different kinds of cells, they all have some essential features that link them all together under the category of "life."  One of the most important parts of a cell is the membrane that surrounds it, seperating it from the rest of the environment.

While organisms from the three main domains live in incredibly different environments, they all possess similar cell membranes.  This phospholipid bilayer protects the cell, giving it a way to allow certain things in while keeping other things out.  Though organisms from different domains have different kinds of fatty linkages in their membranes, they all serve this essential purpose.

Membranes contain all kinds of essential proteins and signal molecules that allow the inside of the cell to respond to the outside of the cell.  In a multicellular eukaryote, this ability can be used to allow cells to communicate.  In a bacterial colony, an extracellular signal could be used to signal other bacteria.  Signals cascade through a series of molecular pathways that go from the outside of the cell all the way to the nucleus and back out again, giving the cell control on a genetic level.  This allows cellular responses to be quick and effective, and it also allows the cell to control how long it stays in that state.

Fire was once debated over to decide if it should be considered alive or not; however, fire is not made of cells, so it was decided that it was indeed not alive. Which answer choice is NOT a tenet of all living things?

Possible Answers:

All cells contain a nucleus bounded by a membrane.

Cells compose all living things.

The cell is the most fundamental unit of all life.

Cells carry DNA.

All cells come from pre-existing cells.

Correct answer:

All cells contain a nucleus bounded by a membrane.

Explanation:

The four incorrect answers are simply the foundation of the Cell Theory, and you should know them.  While all cells have a membrane enclosing the whole cell, not all have a membrane-bound nucleus.  Prokaryotes have a nucloid that contains most of the genetic material, but it is not bound.

Example Question #1 : Biology

The cell theory describes the properties that are the basis of life. Which of the following is not a tenet of the cell theory?

Possible Answers:

Cells must undergo oxidative phosphorylation to produce energy

All cells come from pre-existing cells

Cells are the basic functional unit of life

Cells carry genetic information in the form of DNA

All living things are made of cells

Correct answer:

Cells must undergo oxidative phosphorylation to produce energy

Explanation:

Not all cells need to undergo oxidative phosphorylation to produce energy; they can also use anaerobic respiration or other methods of energy production.

The cell theory states that all living things are made of one of more cells, and that a cell is the basic functional unit of life. The theory claims that any cell must have originated from a pre-existing cell, detailing the concept of cellular reproduction. These three claims form the broad arc od concepts of the cell theory. Additional sub-claims to the theory dictate that cells contain DNA and require energy (nutrients).

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