Q: Which equation correctly represents the Nernst equation for calculating the equilibrium potential ($E_{ion}$) for a monovalent cation at body temperature?

$E_{ion} = \frac{61}{z} \log_{10} \left( \frac{[\text{ion}]_{out}}{[\text{ion}]_{in}} \right)$

Question 1

Which of the following best describes the function of a negative feedback system in maintaining homeostasis?

Accepted Answer

It reverses the direction of the initial change to return the system to its set point.

Question 2

A patient is experiencing dehydration, leading to increased plasma osmolarity. Which hormone is most likely to be secreted in response, and what is its primary effect?

Accepted Answer

Antidiuretic hormone (ADH); increases water reabsorption in the kidneys

Question 3

Which of the following best characterizes the distribution of sodium ($\mathrm{Na^+}$) and potassium ($\mathrm{K^+}$) ions in the body’s fluid compartments?

Accepted Answer

$\mathrm{Na^+}$ is higher in the extracellular fluid, $\mathrm{K^+}$ is higher in the intracellular fluid.

Question 4

A cell is placed in a hypotonic solution. Predict what will happen to the cell and explain why, using the concept of osmosis.

Accepted Answer

The cell will swell and may burst because water moves into the cell.

Question 5

Which of the following best explains why lipid-soluble messengers can act on intracellular receptors, while water-soluble messengers cannot?

Accepted Answer

Lipid-soluble messengers can diffuse through the plasma membrane, but water-soluble messengers cannot.

Question 6

During the depolarization phase of an action potential, which ion channels open and what is the resulting movement of ions?

Accepted Answer

Voltage-gated sodium channels open; $\mathrm{Na^+}$ moves into the cell.

Question 7

A patient has a mutation that causes their sodium-potassium pump ($\mathrm{Na^+/K^+}$ ATPase) to be nonfunctional. Which of the following would most likely occur?

Accepted Answer

The cell would accumulate $\mathrm{Na^+}$ inside and lose $\mathrm{K^+}$, disrupting membrane potential.

Question 8

Which of the following is an example of a positive feedback mechanism in the human body?

Accepted Answer

Release of oxytocin during childbirth to intensify uterine contractions

Question 9

Which equation correctly represents the Nernst equation for calculating the equilibrium potential ($E_{ion}$) for a monovalent cation at body temperature?

Accepted Answer

$E_{ion} = \frac{61}{z} \log_{10} \left( \frac{[	ext{ion}]_{out}}{[	ext{ion}]_{in}} ight)$

Question 10

A neuron is exposed to a toxin that blocks voltage-gated potassium channels. What effect will this have on the action potential?

Accepted Answer

The neuron will be unable to repolarize efficiently, prolonging the action potential.

Question 11

Which of the following best describes the role of second messengers in signal transduction?

Accepted Answer

They relay signals from membrane receptors to target molecules inside the cell.

Question 12

A patient is found to have low plasma calcium ($\mathrm{Ca^{2+}}$) levels. Which hormone is most likely to be secreted in response, and what is its effect?

Accepted Answer

Parathyroid hormone; increases calcium release from bones

Question 13

Which of the following best explains why the resting membrane potential of a neuron is close to the equilibrium potential of potassium ($E_K$)?

Accepted Answer

The membrane is much more permeable to $\mathrm{K^+}$ than $\mathrm{Na^+}$ at rest.

Question 14

Which of the following scenarios best illustrates the concept of homeostasis?

Accepted Answer

A person’s blood glucose rises after a meal and is then brought back to normal by insulin secretion.

Question 15

Which of the following best describes the process of up-regulation in cellular signaling?

Accepted Answer

An increase in the number of receptors on the cell surface in response to low ligand concentration.

Question 16

A patient is given an intravenous solution of 0.9% NaCl (normal saline). Which statement best explains why this solution is considered isotonic to human cells?

Accepted Answer

It has the same osmolarity as plasma, so there is no net movement of water into or out of cells.

Question 17

Which of the following is the correct sequence of events in a typical negative feedback loop?

Accepted Answer

Sensor → Integrator → Effector → Response

Question 18

Which of the following best describes facilitated diffusion across a cell membrane?

Accepted Answer

Movement of molecules from high to low concentration through a protein channel, without ATP.

Question 19

A patient with severe diarrhea is losing large amounts of bicarbonate ($\mathrm{HCO_3^-}$) in their stool. What acid-base disturbance are they most at risk for developing?

Accepted Answer

Metabolic acidosis

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