AP Biology : 4.5 Feedback - Exam Style questions with Answer- MCQ

AP PhysicsAP Calculus AP ChemistryAP Biology

Question

Phosphofructokinase $(PFK)$ is a key enzyme in glycolysis. $ATP$ is one of the two substrates for the reaction catalyzed by $PFK$ . $ATP$ is also an allosteric regulator of $PFK$ . Figure 1 shows the enzyme-substrate interactions of $PFK$

The figure presents enzyme substrate interactions of P F K. The diagram consists of three stages. From left to right, the stages are as follows. In the first stage, a P F K enzyme is shown, with labels indicating the active site and an allosteric site. In the second stage, A T P approaches the allosteric site. In the third stage, A T P is bound in the allosteric site, and the active site has become distorted, resulting in the inability of a substrate to bind to the active site.

Figure 1. The enzyme-substrate interactions of $PFK$

A researcher found a mutation that resulted in the $PFK$ enzyme being unable to bind $ATP$ to the allosteric site. Which of the following best predicts the effect of the mutation?

A. The activity of the enzyme will not be affected because the active site is not involved in substrate binding at the allosteric site.

B. Negative feedback regulation does not occur, so the enzyme will be active when glycolysis is not needed.

C. Positive feedback does not occur, and the activity of the enzyme will decrease when glycolysis is needed.

D. The activity of the enzyme will fluctuate independent of the $ATP$ concentration.

▶️Answer/Explanation

Ans: B
The reaction is normally inhibited when $ATP$ binds to the allosteric site and changes the shape of the active site to the point where it can no longer bind to the substrate. The mutation will not allow this inhibition to occur, and the enzyme will be active even at high $ATP$ concentrations.

Question

A person’s blood glucose level fluctuates during the day, as represented in Figure 1. Two hormones, insulin and glucagon, are directly involved in regulating the blood glucose level to maintain a healthy level. Insulin acts to lower the blood glucose level, and glucagon acts to increase the blood glucose level.

The figure presents a line graph of blood glucose fluctuations of an individual. The horizontal axis is labeled Time, and the times 6 A M through 2 P M are indicated, in increments of 2 hours. The vertical axis is labeled Blood Glucose Levels, in milligrams per deciliter, and the numbers 60 through 140, in increments of 20, are indicated. The graph indicates that meals occurred at 6 A M and 11 A M. The data represented by the line are as follows. Note that all values are approximate. The line begins at 6 A M and 80 milligrams per deciliter, and steeply moves upward and to the right until it reaches 7 A M and 130 milligrams per deciliter. It then moves steeply downward and to the right until it reaches 8 A M and 80 milligrams per deciliter. The line moves gradually downward and to the right until it reaches 11 A M and 70 milligrams per deciliter. The line then moves upward and to the right until it reaches 12:30 P M and 130 milligrams per deciliter. The line steeply moves downward and to the right until it ends at 2 P M and 75 milligrams per deciliter.

Figure 1. Blood glucose fluctuations of an individual
Which of the following best predicts what will happen to the blood glucose level if the person has another meal at 5 p.m.?

A. Immediately after the meal, the blood glucose level will decrease because of the increase in glucagon levels.

B. Immediately after the meal, the blood glucose level will increase, and then insulin will be secreted to counter the increase.

C. Several hours after the meal, the blood glucose level will increase sharply because of an increase in the amount of glucagon secreted.

D. The blood glucose level will not change after the 5 p.m. meal because the person has already consumed two meals and the blood glucose level has been adjusted to a steady-state level.

▶️Answer/Explanation

Ans: B
The blood glucose levels increase due to the nutrients taken in. This increase is a signal for the pancreas to release more insulin that will stimulate cells to take in the excess glucose. As a result, the blood glucose level will then decrease.

Question

Blood clots are formed by a positive feedback loop. Two pathways exist, the extrinsic and intrinsic pathways, which converge during clot formation. There are many clotting factors involved, most of which are proteins. Vitamin $K$ is required for the formation of the active form of several of the clotting factors, including Factor $X$ . A simplified model of the blood clotting process is shown in Figure 1.

The figure presents a simplified model of the clotting cascade. The model is as follows. Two pathways, the extrinsic pathway and the intrinsic pathway, converge to cause clot formation. The extrinsic pathway begins with damage to the tissue outside a vessel which initiates the release of thromboplastin from the tissue. The intrinsic pathway begins with damage to a blood vessel which triggers a cascade of clotting factors. The thromboplastin and the cascade of clotting factors both mediate the conversion of inactive Factor 10 to activated Factor 10. Activated Factor 10 then triggers the conversion of Prothrombin to Thrombin. Thrombin then triggers the conversion of Fibrinogen to Fibrin. Factor 13 interacts with Fibrin to produce a blood clot.

Warfarin is a drug used to treat certain blood clots. Warfarin blocks the formation of the active form of vitamin

K

-dependent clotting factors. Based on the model, which of the following best predicts the effects of warfarin on a patient?

A. Fibrinogen will form fibrin, but the clot will not form because Factor

XIII

will not be synthesized.

B. The intrinsic pathway will take over because the clotting factors are part of that pathway.

C. Thrombin will be converted to prothrombin because Factor

X

will reverse the reaction.

D. Factor

X

will not be activated, which will prevent thrombin from forming.

▶️Answer/Explanation

Ans: D
Vitamin $K$ is required for the synthesis of Factor $X$ and warfarin inhibits that process; thus, clots are prevented from forming.

Question

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1.

The figure presents a simplified model of the epinephrine signaling pathway in muscle cells. A plasma membrane is shown with two transmembrane structures, a Beta-2 Adrenergic Receptor and Adenylyl Cyclase. Epinephrine is shown binding to the extracellular surface of the beta-2 adrenergic receptor. Bound to the cytosolic surface of the receptor is a G protein made up of alpha, beta, and gamma subunits. An arrow indicates that G D P that is bound to the alpha subunit of the G protein is now released from the subunit. A successive arrow points to the G protein subunits dissociated from the adrenergic receptor and the alpha subunit dissociated from a complex of the beta and gamma subunits. G T P is shown binding to the alpha subunit. A successive arrow points from the G T P-modified alpha subunit to the cytosolic region of adenylyl cyclase. Adenylyl cyclase intersects an arrow that points from A T P to Cyclic A M P. A series of arrows follows. An arrow from Cyclic A M P points to Protein Kinase A. An arrow from Protein Kinase A points to Phosphorylase Kinase and is paired with a curved arrow pointing from A T P to A D P. An arrow from Phosphorylase Kinase points to Glycogen Phosphorylase and is paired with a curved arrow pointing from A T P to A D P. An arrow from Glycogen Phosphorylase points to an arrow indicating the conversion of Glycogen to Glucose-1-Phosphate. A final arrow points from Glucose-1-Phosphate to Glycolysis.

Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells Cyclic $AMP$ phosphodiesterase is an enzyme that catalyzes the conversion of cyclic $AMP$ to a different molecule. Which of the following best predicts the effect of inhibiting cyclic $AMP$ phosphodiesterase in a muscle cell stimulated by epinephrine?

A. The concentration of cyclic $AMP$ will decrease because adenylyl cyclase will no longer be activated.

B. The G protein will diffuse out of the cell because it will no longer bind to the plasma membrane.

C. Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated.

D. Glycolysis will stop because epinephrine signaling will no longer stimulate glycogen breakdown.

▶️Answer/Explanation

Ans: C
Phosphorylase kinase is activated by protein kinase A, which is activated by binding to cyclic $AMP$ . Cyclic $AMP$ phosphodiesterase causes the deactivation of protein kinase A by lowering the intracellular levels of cyclic $AMP$ . Inhibiting cyclic $AMP$ phosphodiesterase will result in protein kinase A remaining active, which will result in phosphorylase kinase remaining active.

Question

Figure 1 is a proposed model of the feedback system controlling erythrocyte (red blood cell) production.

Figure 1. Model of erythrocyte production control

Air is less dense at very high elevations, so less oxygen is available than in the denser air at sea level. Based on the model in Figure 1, if a person travels from sea level to a high elevation location, which of the following correctly predicts the response to the decreased blood oxygen level?

A. More erythropoietin will be secreted from the kidneys, decreasing production of erythrocytes.
B. More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.
C. Less erythropoietin will be secreted from the kidneys, decreasing production of erythrocytes.
D. Less erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.

▶️Answer/Explanation

Ans: B
Erythropoietin production is triggered by a negative feedback mechanism. When kidney cells detect low oxygen levels, the kidney secretes more erythropoietin, which triggers the bone marrow to increase erythrocyte production.

AP Biology : 4.5 Feedback – Exam Style questions with Answer- MCQ

Question

Question

Question

Question

Question

Need Help ? Book A Tutor