All questions of Transport Across a Cell Membrane for MCAT Exam

Cholera affects millions of people around the world. It causes diarrhea, which can lead to dehydration and even death. Cholera toxin affects a chloride transporter that secretes chloride ion into the lumen of the small intestine. How does cholera toxin lead to dehydration?
a)
The toxin turns off the transporter, so the negatively charged chloride pushes water into the lumen
b)
The toxin turns on the transporter, and water follows the ion due to osmosis
c)
The toxin turns on the transporter, and water is actively transported with the ion
d)
The toxin turns off the transporter, so water is no longer exchanged for chloride ion
Correct answer is option 'B'. Can you explain this answer?

Isaac Bailey answered

Understanding Cholera Toxin and Dehydration
Cholera is caused by the bacterium Vibrio cholerae, which produces a potent toxin that disrupts normal intestinal function. This leads to severe dehydration, a life-threatening condition.
Mechanism of Cholera Toxin
- Cholera toxin binds to intestinal epithelial cells, leading to the activation of adenylate cyclase.
- This increases cyclic AMP (cAMP) levels in the cell, which in turn activates protein kinase A (PKA).
Effect on Chloride Transporter
- The activated PKA phosphorylates the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride ion channel.
- This phosphorylation opens the CFTR channel, resulting in increased secretion of chloride ions (Cl-) into the intestinal lumen.
Role of Water and Osmosis
- As chloride ions are secreted into the lumen, water follows due to osmosis.
- Osmosis is the movement of water from areas of lower solute concentration (inside the cells) to areas of higher solute concentration (the intestinal lumen where chloride concentration is increased).
- Consequently, this leads to massive water loss from the body, resulting in severe diarrhea and dehydration.
Conclusion
- Thus, the correct answer is option 'B': "The toxin turns on the transporter, and water follows the ion due to osmosis."
- This critical mechanism underscores the importance of rapid rehydration and medical intervention in cholera cases to prevent death.

View Answers

Join for Free

Which transport process is responsible for the movement of gases such as oxygen and carbon dioxide across the cell membrane?
a)
Diffusion
b)
Osmosis
c)
Facilitated diffusion
d)
Active transport
Correct answer is option 'A'. Can you explain this answer?

Orion Classes answered

Diffusion is the process responsible for the movement of gases such as oxygen and carbon dioxide across the cell membrane, as they passively move from areas of high concentration to low concentration.

View Answers

Selective serotonin reuptake inhibitors (SSRIs), used to treat depression, block a specific protein in the pre-synaptic neuron to keep the neurotransmitter in the synaptic cleft for a longer period of time. What sort of protein do they block?
a)
A neurotransmitter ATP pump
b)
A phagocytosis-inducing protein
c)
A sodium-neurotransmitter symporter
d)
A neurotransmitter channel
Correct answer is option 'C'. Can you explain this answer?

Orion Classes answered

Selective serotonin reuptake inhibitors (SSRIs) work by blocking the reuptake of serotonin, a neurotransmitter, in the pre-synaptic neuron. They specifically target and block the serotonin transporter protein, which is a sodium-neurotransmitter symporter. This protein is responsible for the reabsorption of serotonin from the synaptic cleft back into the pre-synaptic neuron. By blocking this transporter, SSRIs increase the concentration of serotonin in the synaptic cleft, allowing it to interact with and stimulate the post-synaptic receptors for a longer period of time. This helps alleviate symptoms of depression and improve mood.

View Answers

Pulmonary edema occurs when fluid builds up in the interstitium between the pulmonary capillaries and the alveoli, and eventually enters the alveoli. How do you decrease the risk of pulmonary edema?
a)
Decrease hydrostatic pressure and increase osmotic pressure
b)
Increase hydrostatic pressure and decrease osmotic pressure
c)
Decrease hydrostatic pressure and decrease osmotic pressure
d)
Increase hydrostatic pressure and increase osmotic pressure
Correct answer is option 'A'. Can you explain this answer?

Orion Classes answered

Pulmonary edema is the accumulation of fluid in the lungs, specifically in the interstitium and alveoli. To decrease the risk of pulmonary edema, it is necessary to address the factors that contribute to the movement of fluid into the interstitium and alveoli.

Hydrostatic pressure refers to the pressure exerted by fluid within blood vessels, and it tends to push fluid out of the vessels and into the surrounding tissues. To reduce the risk of pulmonary edema, it is important to decrease hydrostatic pressure, which can be achieved by improving heart function, reducing fluid volume, or relieving any obstructions or pressures on blood vessels in the lungs.

Osmotic pressure, on the other hand, is the pressure exerted by solutes (such as proteins) that draw water into the blood vessels. By increasing osmotic pressure, more fluid can be retained within the blood vessels, reducing the likelihood of it leaking into the interstitium and alveoli. This can be accomplished by maintaining adequate levels of proteins, particularly albumin, in the bloodstream.

View Answers

The nephron reabsorbs glucose through a sodium / glucose transporter. What sort of transporter is it?
a)
Protein channel
b)
Antiporter
c)
Sodium pump
d)
ymporter
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered

The sodium/glucose transporter found in the nephron is a symporter. A symporter is a type of transporter protein that simultaneously moves two different molecules across a cell membrane in the same direction. In this case, the transporter moves both sodium ions and glucose molecules from the tubular fluid in the nephron into the cells of the renal tubules. This process is known as co-transport or secondary active transport, as it utilizes the energy stored in the electrochemical gradient of sodium ions to drive the uphill movement of glucose against its concentration gradient. The symporter binds both sodium and glucose on one side of the membrane and undergoes a conformational change to transport them together into the cell. This allows for the efficient reabsorption of glucose from the filtrate back into the bloodstream, helping to maintain glucose homeostasis in the body.

View Answers

Which type of transport process involves the release of large particles or substances from the cell?
a)
Facilitated diffusion
b)
Endocytosis
c)
Exocytosis
d)
Osmosis
Correct answer is option 'C'. Can you explain this answer?

Orion Classes answered

Exocytosis is the process by which cells release large particles or substances from the cell by fusing vesicles containing the material with the cell membrane and expelling the contents outside the cell.

View Answers

What cell membrane property in the nephron capillaries allows small molecules to pass through?
a)
It has cholesterol rafts
b)
It has glycoprotein channels
c)
It has fenestrations
d)
It is amphipathic
Correct answer is option 'C'. Can you explain this answer?

Orion Classes answered

Fenestrations are small pores or openings in the endothelial cells lining the capillaries of the nephron. These fenestrations allow small molecules to pass through the capillary walls and enter the surrounding tissues. The presence of fenestrations increases the permeability of the capillaries, allowing for the filtration and exchange of small molecules, such as water, ions, and nutrients, between the blood and the surrounding tissues. This property is important in the function of the nephron, as it allows for the filtration of waste products and the reabsorption of essential substances during urine formation.

View Answers

What sort of transporters would be required to move glucose from the blood to the lumen?
a)
Apical sodium/glucose symporter and basolateral sodium/potassium pump and glucose channel
b)
Apical glucose channel and basolateral sodium/potassium pump and sodium/glucose symporter
c)
Apical glucose channel and basolateral sodium/potassium pump and sodium/glucose antiporter
d)
Apical sodium/glucose antiporter and basolateral sodium/potassium pump and glucose channel
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered

The apical side faces the lumen, while the basolateral side of the cell is the one closer to the capillary system.
There is effectively no glucose inside the cell.
To bring glucose into the cell requires some amount of energy.
To bring glucose from the blood to the cell, a basolateral glucose channel will allow glucose to move down its gradient. An apical sodium/glucose antiporter will move glucose against its gradient by using the energy of sodium following its gradient. A sodium/potassium pump maintains sodium concentration.

View Answers

Immune system cells use damaging proteases and reactive oxygen species to destroy foreign invaders. The immune system cells are not harmed because the microbes are sequestered in vesicles. How did the invaders get to the vesicles?
a)
Active transport
b)
Phagocytosis
c)
Exocytosis
d)
Pinocytosis
Correct answer is option 'B'. Can you explain this answer?

Orion Classes answered

In the context of the immune system, phagocytosis is the process by which immune cells engulf and internalize foreign invaders such as microbes. During phagocytosis, the immune cell surrounds the invader and forms a vesicle called a phagosome. The phagosome then fuses with lysosomes, forming a phagolysosome, where damaging proteases and reactive oxygen species are released to destroy the invaders.

So, the invaders reach the vesicles through phagocytosis. The immune cells recognize the presence of foreign substances and actively engulf them by extending pseudopods to surround the invaders and internalize them into vesicles for destruction. This sequestration in vesicles allows the immune system to isolate and neutralize the invaders while minimizing harm to the surrounding cells.

View Answers

How do potassium ions travel as they move into the cell?
a)
Down the concentration gradient and up the membrane potential
b)
Up the concentration gradient and down the membrane potential
c)
Down the concentration gradient and down the membrane potential
d)
Up the concentration gradient and up the membrane potential
Correct answer is option 'B'. Can you explain this answer?

Orion Classes answered

Potassium ions (K⁺) move into the cell by a process known as facilitated diffusion, which involves the movement of ions from an area of higher concentration to an area of lower concentration. In the case of potassium ions, they move from the extracellular fluid, where their concentration is higher, to the intracellular fluid, where their concentration is lower.

The movement of potassium ions is also influenced by the membrane potential, which is the difference in electrical charge across the cell membrane. The inside of the cell is negatively charged compared to the outside. This electrical gradient tends to attract positively charged potassium ions into the cell.

Therefore, the overall movement of potassium ions involves moving up the concentration gradient (from high to low concentration) and down the membrane potential (from a more positive to a less positive or negative potential) to enter the cell.

View Answers

Chapter doubts & questions for Transport Across a Cell Membrane - Biology for MCAT 2025 is part of MCAT exam preparation. The chapters have been prepared according to the MCAT exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for MCAT 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.

Chapter doubts & questions of Transport Across a Cell Membrane - Biology for MCAT in English & Hindi are available as part of MCAT exam. Download more important topics, notes, lectures and mock test series for MCAT Exam by signing up for free.