MCAT Biology : Other Concepts

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Other Concepts

Thermoregulation of the human body is controlled by a __________.

Possible Answers:

set of hormones

biological rhythm

negative feedback mechanism

None of these answers

positive 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 #5 : Biology

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

Hyperosmotic

Hypotonic

Hypertonic

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 #6 : Biology

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 glucose solution will be at a higher level

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

The sodium hydroxide solution will be at a higher level

The two solutions will be at the same height

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 #2 : Other Concepts

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 come from pre-existing cells.

Cells compose all living things.

The cell is the most fundamental unit of all life.

All cells contain a nucleus bounded by a membrane.

Cells carry DNA.

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 #3 : Other Concepts

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 carry genetic information in the form of DNA

Cells are the basic functional unit of life

Cells must undergo oxidative phosphorylation to produce energy

All living things are made of cells

All cells come from pre-existing 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).

Example Question #2 : Other Concepts

Which fo the following marks a distinct quality of smooth muscle?

Possible Answers:

It contains specialized gap junctions

It fatigues rapidly 

It contains striations and intercalated discs

It develops tension slowly, but maintains contractions longer

It develops tension quickly, but maintains contractions longer

Correct answer:

It develops tension slowly, but maintains contractions longer

Explanation:

Smooth muscle varies from other muscle types because it has the capacity to develop tension slowly, but maintain contractions for a longer period. The autorhythmic cells within smooth muscle generate slow wave or pacemaker potentials that allow tension to develop slowly. Think, for example, of the smooth muscle that surrounds the bladder and generates tension slowly or of the smooth muscle that controls the size of the pupil and must maintain contractions for extended periods.

Example Question #3 : Other Concepts

A man must have his duodenum completely removed. During the surgery, the stomach will be connected to the jejunum. As a result of the surgery, the patient will likely suffer from which of the following conditions?

Possible Answers:

Inability to convert polysaccharides to disaccharides

Inability to produce bile

Inability to synthesize vitamin K

Inability to digest lipids

Deficiency in water absorption

Correct answer:

Inability to digest lipids

Explanation:

The duodenum and jejunum are two adjacent regions of the small intestine. The duodenum is the region in which the majority of chemical digestion occurs. The pancreas secretes several critical digestive enzymes into the duodenum. One of these enzymes is lipase, which is responsible for lipid digestion. Removal of this region would result in an inability to digest lipids.

Production of vitamin K mostly occurs in the large intestine, digestion of polysaccharides to disaccharides is accomplished with salivary amylase, water absorption occurs in the large intestine, and bile is produced by the liver.

Example Question #4 : Other Concepts

A vitamin is defined as an organic molecule that is required to be obtained from the diet because it cannot be synthesized by the organism. Based on this definition, which of the following is not a true vitamin?

Possible Answers:

Vitamin A

Vitamin E

Vitamin C

Vitamin D

Correct answer:

Vitamin D

Explanation:

Although there are recommended intake values for vitamin D, this "vitamin" can be synthesized by the body with the help of UV radiation from the sun. 

Example Question #4 : Other Concepts

Certain inhibitors bind enzymes irreversibly through covalent bonding. Would the kinetics (V vs. [S] curve) of this be similar to that of a reversible noncompetitive inhibitor? Why?

Possible Answers:

Yes, since the total effect would result in a loss of usable enzymes for the reaction

 No, since the total effect would result in a loss of usable enzymes for the reaction

Yes, since the  will be increased

 No, since the  will be reduced

None of these

Correct answer:

Yes, since the total effect would result in a loss of usable enzymes for the reaction

Explanation:

An irreversible noncompetitive inhibitor permanently deactivates some enzyme function. Therefore, the effective enzyme concentration will be reduced, which is also what is observed through using a reversible noncompetitive inhibitor.  is unaffected by noncompetitive inhibitors.

Example Question #6 : Other Concepts

Which of the following types of enzymes irreversibly modifies its substrate?

Possible Answers:

 Kinase

All of these

Protease

Phosphatase

Ligase

Correct answer:

Protease

Explanation:

Proteases are enzymes that cleave substrates at certain locations. This permanently removes a part of the protein and thus is irreversible. Kinases catalyze the phosphorylation of proteins. Since phosphatases do the opposite, we know that phosphate groups can be reversibly added to proteins. Ligases catalyze the joining of two molecules together, which is reversible since large dimers and polymers are broken down all the time.

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