MCAT Biology : MCAT Biological Sciences

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #2 : Pulmonary And Systemic Circuits

Which of the following vessels is not involved in the systemic circulation?

Possible Answers:

Hepatic portal capillaries

The vasa recta

Femoral artery

Pulmonary veins

Correct answer:

Pulmonary veins

Explanation:

The systemic circulation refers to the path that carries blood from the left ventricle, through the body, back to the right atrium. In contrast, the pulmonary circuit refers to the path from the right ventricle, through the lungs, and back to the left atrium.

The femoral artery is a major systemic artery found in the leg and thigh. The hepatic portal system delivers oxygenated blood to the liver. The vasa recta refers to the capillaries surrounding the nephrons in the kidney, which help to regulate the ion gradient responsible for concentrating urine.

The pulmonary veins carry oxygenated blood from the lungs to the left atrium, and are part of the pulmonary circuit.

Example Question #1 : Pulmonary And Systemic Circuits

An obstruction in the pulmonary artery would cause an immediate increase in blood pressure which region?

Possible Answers:

Left ventricle

Pulmonary veins

Right atrium

Right ventricle

Correct answer:

Right ventricle

Explanation:

When an obstruction causes a restriction of flow, increased pressure will occur upstream of the blockage. In the cardiopulmonary system blood flows from the right atrium to the right ventricle, then through the pulmonary artery, lungs, and pulmonary vein, before re-entering the heart at the left atrium.

Should a blockage occur in the pulmonary artery, blood will pool behind the blockage (upstream) in the right ventricle, increasing the pressure in this chamber.

Example Question #911 : Mcat Biological Sciences

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 optimized 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

 

Hemoglobin binding to oxygen is dependent on oxygen partial pressure, as depicted in the above graph. Where is oxygen partial pressure likely to be the highest?

Possible Answers:

Tissue arterioles

Venules

Aorta

Lung capillaries

Capillaries

Correct answer:

Lung capillaries

Explanation:

Oxygen partial pressure is likely to be highest in the lung capillaries, as this is where oxygen will be "loaded" on to hemoglobin molecules for transportation to the tissues. Since binding affinity increases with oxygen partial pressure, one would also expect red blood cells in lung capillaries to bind the strongest to oxygen, which allows hemoglobin saturation in the lungs.

Example Question #5 : 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

Right atrium

Left ventricle

Left atrium

Right ventricle and left 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 #891 : Biology

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:

Left ventricle 

None of these

Superior vena cava 

Foramen spinosum

Aorta

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 #12 : 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.

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

Possible Answers:

Inferior vena cava 

Right atrium

Pulmonary artery 

Left ventricle 

Right 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:

Adipocytes

Epithelial cells

Enterocytes

Red blood cells

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 #2 : 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:

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

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.

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 #881 : Systems Biology And Tissue Types

Which factors contribute to the Bohr Effect?

Possible Answers:

Low pH, high CO2, low temperature

High pH, low CO2

Low pH, low CO2

Low pH, high CO2

Low pH, high CO2, high temperature

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:

Level of solubility

Ability to reversibly bind oxygen

Peptide nature

Cooperativity

Iron-binding capacity

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.

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