MCAT Biology : Biology

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #3 : Pulmonary And Systemic Circuits

A man is diagnosed with increased pulmonary capillary resistance. As a result, which part of the heart would be expected to increase in muscle mass?

Possible Answers:

Right ventricle

Left ventricle

Left atrium

Right ventricle and left atrium

Right atrium

Correct answer:

Right ventricle

Explanation:

Increased pulmonary resistance means that it will be more difficult to pump blood into the lungs. The right ventricle, which performs this function, will compensate by increasing in muscle mass. The left atrium will not increase in muscle mass because it receives blood from the lungs and pumps blood into the left ventricle; its muscle mass will likely be unaffected.

Example Question #11 : Pulmonary And Systemic Circuits

The brain is a very delicate structure with little room to move around. Surrounding the brain and the spinal cord are three protective layers in addition to the skull and the vertebral column. Directly surrounding the brain and spinal cord is the pia mater. Following the pia mater is the arachnoid mater. Between the pia mater and the arachnoid mater is the sub-arachnoid space where the cerebrospinal fluid circulates. Finally, the protective layer is the dura mater is loosely attached to the arachnoid mater but is strongly associated with the skull bone.

Depending on the type of injury, a certain type of vein and/or artery are more susceptible to injury. For example, the meningeal artery and vein run through the foramen spinosum and travel between the two layers making up the dura mater. As the artery and the vein are traveling in between the dura mater, there is a vulnerable region at the temple. A strike to the temple region could rupture these vessels and result in a epidural hematoma. 

Traveling from the cerebral cortex to the venous dural sinus (located at certain regions between the two layers of the dura mater) is the cerebral vein. When an injury results in the dura mater shifting away from the arachnoid mater, the cerebral vein could rupture and lead to a subdural hematoma.

According to the passage, the cerebral vein will ultimately drain into which structure?

Possible Answers:

None of these

Left ventricle 

Superior vena cava 

Aorta

Foramen spinosum

Correct answer:

Superior vena cava 

Explanation:

All of the venous blood will ultimately drain into the vena cava. From the vena cava, blood is then drained into the right atrium, the right ventricle, the pulmonary artery and finally to the lungs to exchange carbon dioxide for oxygen.

Example Question #63 : Circulatory System

The brain is a very delicate structure with little room to move around. Surrounding the brain and the spinal cord are three protective layers in addition to the skull and the vertebral column. Directly surrounding the brain and spinal cord is the pia mater. Following the pia mater is the arachnoid mater. Between the pia mater and the arachnoid mater is the sub-arachnoid space where the cerebrospinal fluid circulates. Finally, the protective layer is the dura mater is loosely attached to the arachnoid mater but is strongly associated with the skull bone.

Depending on the type of injury, a certain type of vein and/or artery are more susceptible to injury. For example, the meningeal artery and vein run through the foramen spinosum and travel between the two layers making up the dura mater. As the artery and the vein are traveling in between the dura mater, there is a vulnerable region at the temple. A strike to the temple region could rupture these vessels and result in a epidural hematoma. 

Traveling from the cerebral cortex to the venous dural sinus (located at certain regions between the two layers of the dura mater) is the cerebral vein. When an injury results in the dura mater shifting away from the arachnoid mater, the cerebral vein could rupture and lead to a subdural hematoma.

The meningeal artery received its blood supply from which specific structure? 

Possible Answers:

Right ventricle

Inferior vena cava 

Right atrium

Pulmonary artery 

Left ventricle 

Correct answer:

Left ventricle 

Explanation:

Oxygen-rich blood will enter the left atrium, left ventricle, aorta, then to the systemic circulation including the brain.   

Example Question #1 : Hemoglobin, Blood Cells, And Blood Proteins

Bilirubin is a byproduct of heme catabolism, and is excreted in the bile and stool. Bilirubin is likely derived from processes in what cell type?

Possible Answers:

Red blood cells

Adipocytes

Epithelial cells

Enterocytes

Correct answer:

Red blood cells

Explanation:

Heme is an important functional group of hemoglobin. Bilirubin, which is a byproduct of heme breakdown, comes from red blood cells. The liver receives unconjugated bilirubin from the blood and conjugates it via phase II metabolism to make it more soluble for excretion via the bile and stool. Fat cells (adipocytes), skin cells (epithelial cells), and small intestine absorptive cells (enterocytes) do not contain heme to be processed into bilirubin.

Example Question #1 : Hemoglobin, Blood Cells, And Blood Proteins

A fetus does not breathe inside the womb, and so it must obtain oxygen a different way. What property of hemoglobin allows a fetus to recieve the oxyge it needs to develop?

Possible Answers:

Fetal hemoglobin is composed of four subunits while adult hemoglobin is composed of two.

The partial pressure of oxygen in fetal hemoglobin is always the same as that of its mother.

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin.

The partial pressure of oxygen in fetal hemoglobin is always higher than that of its mother.

Fetal hemoglobin has a lower affinity for oxygen than adult hemoglobin.

Correct answer:

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin.

Explanation:

Fetal hemoglobin has a higher affinity for oxygen that adult hemoglobin. Maternal and Fetal blood never mix during pregnancy, but they come close to each other in the placenta.  Oxygen diffuses easily to fetal hemoglobin here. The reason fetal hemoglobin has a higher affinity is it is composed of two alpha and two gamma subunits, while adult hemoglobin is composed of two alpha and two beta subunits.

Example Question #3 : Hemoglobin, Blood Cells, And Blood Proteins

Which factors contribute to the Bohr Effect?

Possible Answers:

Low pH, high CO2, low temperature

Low pH, low CO2

Low pH, high CO2, high temperature

Low pH, high CO2

High pH, low CO2

Correct answer:

Low pH, high CO2

Explanation:

The Bohr Effect describes hemoglobin's affinty for oxygen as a function of blood pH and carbon dioxide content. An increase in CO2 concentration will lower the blood pH, causing the hemoglobin affinity for oxygen to reduce. High temperature also causes oxygen to be released from hemoglobin, but is not related to the Bohr Effect.

Think about when you're exercising. Your blood has a reduced O2 concentration and an elevated CO2 concentration. These factors allow hemoglobin to release more oxygen in the muscles to faciliate ATP production and maintain energy levels.

Example Question #1 : Hemoglobin, Blood Cells, And Blood Proteins

Hemoglobin is the principal oxygen-carrying protein in humans. It exists within erythrocytes, and binds up to four diatomic oxygen molecules simultaneously. Hemoglobin functions to maximize oxygen delivery to tissues, while simultaneously maximizing oxygen absorption in the lungs. Hemoglobin thus has a fundamentally contradictory set of goals. It must at once be opitimized to absorb oxygen, and to offload oxygen. Natural selection has overcome this apparent contradiction by making hemoglobin exquisitely sensitive to conditions in its microenvironment.

One way in which hemoglobin accomplishes its goals is through the phenomenon of cooperativity. Cooperativity refers to the ability of hemoglobin to change its oxygen binding behavior as a function of how many other oxygen atoms are bound to the molecule. 

Fetal hemoglobin shows a similar pattern of cooperativity, but has unique binding characteristics relative to adult hemoglobin. Fetal hemoglobin reaches higher saturation at lower oxygen partial pressure.

Because of cooperativity, adult and fetal oxygen-hemoglobin dissociation curves appear as follows.

Untitled

Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin is given below.

H+ + HbO2 ←→ H+Hb + O2

Myoglobin is a similar carrier molecule to hemoglobin, but it only has one site of oxygen binding instead of four. Which characteristic of hemoglobin is most likely not shared by myoglobin?

Possible Answers:

Ability to reversibly bind oxygen

Iron-binding capacity

Cooperativity

Level of solubility

Peptide nature

Correct answer:

Cooperativity

Explanation:

Cooperativity, as defined in the passage, requires more than one binding site. Without more than one binding site, it is impossible for a carrier to change its affinity for additional cargo after the first piece is either loaded or unloaded. That additional cargo simply doesn't exist for myoglobin.

Example Question #5 : Hemoglobin, Blood Cells, And Blood Proteins

Which of the following gases can be bound by hemoglobin?

Possible Answers:

Oxygen

Carbon dioxide

All of the answers are correct

Carbon monoxide

Correct answer:

All of the answers are correct

Explanation:

All of these gases can be bound by hemoglobin. Hemoglobin transports oxygen from the lungs to the necessary tissue, and carbon dioxide from the tissue to the lungs. Hemoglobin has a much higher affinity for carbon monoxide than oxygen, which is why it is so dangerous to inhale carbon monoxide.

Example Question #2 : Hemoglobin, Blood Cells, And Blood Proteins

Which of the following is most likely to decrease oxygen's affinity to hemoglobin in the bloodstream?

Possible Answers:

Low pH

High pH

Low levels of carbon dioxide

Low temperature

Correct answer:

Low pH

Explanation:

High levels of carbon dioxide (CO2), low pH, and high temperatures all act to decrease oxygen's affinity toward human hemoglobin. Think of working muscle, which produces hot, acidic, high CO2 conditions in the blood; in this environment, it is important for hemoglobin to release transported oxygen to provide an aerobic environment to the muscle.

Example Question #891 : Biology

If an individual's blood has a slightly lower pH than normal, this means that oxygen affinity to hemoglobin __________.

Possible Answers:

decreases

remains the same because only oxygen levels can affect affinity

increases

remains the same because only temperature can affect affinity

remains the same because only carbon dioxide levels can affect affinity

Correct answer:

decreases

Explanation:

A decrease in pH is generally caused by an increase in carbon dioxide in the blood, and will cause hemoglobin to have a lower affinity to oxygen. This makes sense, because we want to easily release oxygen to tissues with high levels of carbon dioxide, and quickly bind and remove the carbon dioxide from the cells to the lungs for expiration from the body.

Increased temperature will also decrease the affinity of hemoglobin for oxygen.

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