MCAT Biology : Biology

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #657 : Systems Biology And Tissue Types

There are a large variety of over-the-counter pregnancy tests, although all of them share a set of common principles.

These home pregnancy tests are immunoassays which detect the presence of the peptide hormone human chorionic gonadotropin (hCG). hCG is produced by the fertilized ovum and released into the mother's bloodstream, preventing the degradation of the corpus luteum and thereby preventing menstruation. By the time of the mother's first missed period, hCG levels in the urine are high enough to detect.

The home pregnancy test generally involves dipping a stick containing immobilized hCG monoclonal antibodies into a urine sample. If hCG is present in the urine, it will bind to the monoclonal antibodies on the dipstick. The dipstick is then placed in a solution containing a second monoclonal antibody which recognizes the bound hCG antibody complex on the surface of the dipstick. This second antibody is conjugated to colloidal gold particles which change color when they are immobilized, indicating a positive test result (i.e., pregnancy).

Why isn't the presence of progesterone used as an indicator of pregnancy in the home pregnancy test?

Possible Answers:

Progesterone is continuously secreted by the adrenal gland and the levels are not subject to any alterations as a result of pregnancy

Progesterone is not made exclusively by the fertilized zygote

Progesterone is not present in the bloodstream

Progesterone is secreted too late in the pregnancy to be of any diagnostic value

All of these

Correct answer:

Progesterone is not made exclusively by the fertilized zygote

Explanation:

In order to be indicative of pregnancy, a hormone must only be produced either by a mother who is pregnant or the fertilized embryo itself. Otherwise, false test results might be possible. Progesterone is normally produced by females who are not pregnant during the course of their monthly menstrual cycles. It is not purely a hormone associated with pregnancy. The other answer choices do not offer valid explanations why progesterone can't be used.

Example Question #21 : Hormone Origins And Targets

Both the sympathetic and the parasympathetic nervous systems are essential for homeostasis and for survival. For example, when we are trying to run away from a threat, the sympathetic nervous system is in full effect to allow us to escape from danger. However, when there is no obvious threat, the parasympathetic nervous system tends to be more in control. 

There are similarities and differences between the sympathetic and the parasympathetic nervous systems. In preganglionic nerve fibers, both the sympathetic and the parasympathetic nervous system utilize the neurotransmitter acetylcholine. Closer to the target organ, the parasympathetic nervous system remains dependent on acetylcholine whereas norepinephrine and epinephrine are the predominant neurotransmitters utilized by the sympathetic nervous system. 

When norepinephrine and epinephrine bind to their receptors, different effects are carried out based on the type of receptor, affinity, and location of the receptor. For example, epinephrine has a higher affinity for the beta-2 receptor. When epinephrine binds to the beta-2 receptor, common effects include vasodilation and bronchodilation. Norepinephrine has a stronger affinity for the alpha-1, alpha-2 and beta-1 receptors. When norepinephrine binds to its receptor, common effects on the body include vasoconstriction (alpha-1), increased heart rate (beta-1) and uterine contraction (alpha-1).

Patient A has a genetic disorder which prevents him from producing sufficient amount of catecholamines. Which of the following events will be affected in this patient.  

I. Digestion

II. Pupil dilation

III. Erection

Possible Answers:

III only

I and II

II and III

I only

II only

Correct answer:

II only

Explanation:

Catecholamines consist of epinephrine and norepinephrine. Without these neurotransmitter, the nervous system cannot illicit a sympathetic response. Of the answer choices, only pupil dilation is an event mediated by the sympathetic nervous system. 

Example Question #21 : Hormones

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.

During a hematoma, the intercranial pressure could increase and push on certain regions of the brain. The compression of a certain region could either excite or inhibit the area. If patient A's laboratory results showed an increase blood concentration of antidiuretic hormone, which region of the brain is being compressed? 

Possible Answers:

Adrenal gland

Posterior pituitary 

Anterior pituitary 

Optic chiasm 

Cerebral cortex 

Correct answer:

Posterior pituitary 

Explanation:

Antidiuretic hormone is produced by the hypothalamus and is released by the posterior pituitary. Therefore, compression either of these structures could provoke the release of antidiuretic hormone.  

Example Question #671 : 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.

During a hematoma, the intercranial pressure could increase and push on certain regions of the brain. The compression of a certain region could either excite or inhibit the area. If patient A's laboratory results showed an increase blood concentration of antidiuretic hormone, which region(s) of the brain could be compressed? 

I. Posterior pituitary 

II. Anterior pituitary 

III. Hypothalamus

Possible Answers:

I and III

I only

III only

III only

II and III

Correct answer:

I and III

Explanation:

Antidiuretic hormone is produced by the hypothalamus and is released by the posterior pituitary. Therefore, compression either of these structures could result in increased blood concentrations of antidiuretic hormone.

Example Question #21 : Hormones

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.

During a hematoma, the intracranial pressure could increase and push on certain regions of the brain. The compression of a certain region could either excite or inhibit the area. If patient A has been diagnosed with Cushing's syndrome (excess cortisol), which region(s) could be compressed? 

Possible Answers:

Posterior pituitary 

Adrenal medulla 

Adrenal cortex

Anterior pituitary 

Pineal gland

Correct answer:

Anterior pituitary 

Explanation:

The anterior pituitary releases adrenocorticotropic hormone (ACTH). ACTH then binds receptors in the adrenal cortex and promotes the release of cortisol.  

Example Question #21 : Hormones

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.

During a hematoma, the intracranial pressure could increase and push on certain regions of the brain. The compression of a certain region could either excite or inhibit the area. If the hematoma is compressing on the anterior pituitary, which of the following hormone(s) could be found in excess in the blood? 

I. Antidiuretic hormone (ADH)

II.Oxytocin 

III. Follicle-stimulating hormone (FSH)

Possible Answers:

III only

I only

II and III

III only

I, II, and III

Correct answer:

III only

Explanation:

Of the answer choices, only FSH is released by the anterior pituitary. To help remember the hormones released by the anterior pituitary, use the mnemonic FLAT PEG: Follicle-stimulating hormone, Luteinizing hormone, Adrenocorticotropic hormone, Thyroid-stimulating hormone, Prolactin, Endorphins, and Growth hormone. Both ADH and oxytocin are released by the posterior pituitary.  

Example Question #661 : Systems Biology And Tissue Types

Which of the following answer choices contains only hormones secreted by the anterior pituitary gland?

Possible Answers:

FSH and ACTH

ADH and ACTH

LH and Oxytocin

TSH and Estrogen

Oxytocin and ADH

Correct answer:

FSH and ACTH

Explanation:

The correct answer choice is the one containing FSH and ACTH. FSH, or Follicle-stimulating hormone, and ACTH, or Adrenocorticotropic hormone, are each secreted by the anterior pituitary gland. The anterior pituitary hormones can be remembered by the mnemonic, FLATPEG (FSH, LH, ACTH, TSH, Prolactin, Endorphins, Growth Hormone). 

Each of the other answer choices contains no more than one anterior pituitary hormone, along with either Estrogen (secreted by the ovaries), Oxytocin (secreted by the posterior pituitary), or ADH/Vasopressin (secereted by the posterior pituitary). 

Example Question #662 : Systems Biology And Tissue Types

Which of the following hormones secreted by the pituitary directly acts on the adrenal cortex as its target?

Possible Answers:

ACTH

ADH

FSH

LH

TSH

Correct answer:

ACTH

Explanation:

The only hormone listed that directly stimulates that adrenal cortex is ACTH, which stands for Adrenocorticotropic Hormone. This anterior pituitary-secreted hormone stimulates the adrenal cortex to release cortisol.

The other hormones listed are also secreted by the pituitary gland, but do not act on the adrenal cortex directly. 

Example Question #662 : Systems Biology And Tissue Types

Passage:

In a fictional universe, a new life form is discovered that appears to have a number of similarities to humans. Since its discovery by humans, it has been studied with x-ray imaging, magnetic resonance imaging (MRI), computed tomography imaging (CT), as well as with blood chemistries and laboratory studies. Based upon such analyses, scientists have found that both structurally and functionally, this fictional species, called Lorempis marengis, is highly similar to humans. It has structures that appear similar to lungs that are active during respiration. It has a structure that is highly active at all times, especially so in different parts during different activities (similar to the human brain). It also appears to have a digestive tract with a mouth, esophagus, stomach, small intestine, large intestine, and anus that is assumed to carry out the same functions at the cellular level as the parts of the human digestive tract. Scientists are now hoping to continue studying the organism at the cellular level to confirm their assumption that the cellular functions are indeed similar to those of human tissues.

If we assume that the endocrine anatomy, structure, and function in Lorempis marengis is identical to that of humans, which of the following choices correctly lists two hormones secreted by the posterior pituitary gland in Lorempis marengis?

Possible Answers:

Oxytocin and ACTH

FSH and LH

ADH and ACTH

ACTH and TSH

Oxytocin and Vasopressin

Correct answer:

Oxytocin and Vasopressin

Explanation:

The only answer choice that correctly lists two hormones secreted by the posterior pituitary gland in Lorempis marengis is the choice that includes Oxytocin and Vasopressin. This answer choice is correct because we are told in the question stem to assume that the endocrine anatomy, structure, and function in Lorempis marengis is identical to that of humans, and in humans, both Oxytocin and Vasopressin are secreted by the posterior pituitary gland.

Oxytocin and Vasopressin (also known as Anti-diuretic hormone, or ADH) are the two hormones secreted by the posterior pituitary gland.

Each of the other choices contains either a posterior pituitary and an anterior pituitary secreted hormone, or two hormones secreted by the anterior pituitary. 

The hormones secreted by the anterior pituitary can be remembered by the mnemonic, FLATPEG (FSH, LH, ACTH, TSH, Prolactin, Endorphin, and Growth Hormone). 

Example Question #62 : Endocrine System

All of the following are expected to increase after a meal has been consumed except __________.

Possible Answers:

glucagon

insulin

secretin

cholecystokinin

GLUT-4 receptors

Correct answer:

glucagon

Explanation:

When an a meal is consumed, the digestive system is stimulated. This causes the release of secretin and cholecystokinin, hormones that are involved in digestion. Once glucose is in the bloodstream, it interacts with beta cells and causes the release of insulin. Insulin enters the bloodstream and stimulates widespread expression of the GLUT-4 receptor. Glucagon, on the other hand, counters the effects of insulin in a negative feedback loop and would not be expected to increase after a meal is consumed.

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