Q: A cell is placed in a solution containing 0.15 mol/L NaCl and 0.10 mol/L glucose. Assuming complete dissociation, what is the total osmolarity of the solution?

$$0.15 \times 2 + 0.10 \times 1 = 0.30 + 0.10 = 0.40$$ Osm/L $$= 400$$ mOsm/L

Q: A solution contains 0.10 mol/L MgCl$$ _2 . $$Assuming complete dissociation, what is its osmolarity?

$$0.10 \times 3 = 0.30$$ Osm/L $$= 300$$ mOsm/L

Question 1

Which structural feature of the plasma membrane most directly restricts the passage of charged ions such as Na$$ ^+ $$ through the bilayer?

Accepted Answer

The hydrophobic interior formed by phospholipid tails

Question 2

A cell is placed in a solution containing 0.15 mol/L NaCl and 0.10 mol/L glucose. Assuming complete dissociation, what is the total osmolarity of the solution?

Accepted Answer

$$0.15 	imes 2 + 0.10 	imes 1 = 0.30 + 0.10 = 0.40$$ Osm/L $$= 400$$ mOsm/L

Question 3

Which process is responsible for the selective uptake of LDL cholesterol into cells, and what is the key mechanism?

Accepted Answer

Receptor-mediated endocytosis; cargo binds specific receptors and is concentrated in coated pits

Question 4

A neuron’s membrane contains open K$$ ^+ $$ channels. The concentration gradient favors K$$ ^+ $$ leaving the cell, but the negative interior attracts K$$ ^+ $$ inward. What determines the net direction of K$$ ^+ $$ movement?

Accepted Answer

The combined electrochemical gradient

Question 5

Carrier-mediated transport of glucose via GLUT proteins saturates at high glucose concentrations. What is the primary reason for this saturation?

Accepted Answer

A limited number of carriers and their maximum cycling rate restrict transport capacity

Question 6

During intestinal glucose absorption, which transporters are involved at the apical and basolateral surfaces, and what are their mechanisms?

Accepted Answer

Apical SGLT1: secondary active transport; basolateral GLUT2: facilitated diffusion

Question 7

A cell with 300 mOsm/L nonpenetrating solutes is placed in a solution with 200 mOsm/L nonpenetrating solutes. What is the expected effect on cell volume, assuming water can cross freely?

Accepted Answer

Water enters the cell and it swells

Question 8

Which statement best describes the Na$$ ^+ /K$ ^+ -$$ATPase pump’s activity during one complete cycle?

Accepted Answer

3 Na$$ ^+ $$ out, 2 K$$ ^+  in$$, and 1 ATP used

Question 9

A solution contains 0.10 mol/L MgCl$$ _2 . $$Assuming complete dissociation, what is its osmolarity?

Accepted Answer

$$0.10 	imes 3 = 0.30$$ Osm/L $$= 300$$ mOsm/L

Question 10

A white blood cell engulfs a bacterium by extending pseudopodia and enclosing it in a vesicle. Which transport process is this?

Accepted Answer

Phagocytosis

Question 11

A solution contains 300 mOsm/L NaCl (nonpenetrating) and 100 mOsm/L urea (penetrating). A cell with 300 mOsm/L nonpenetrating solutes is placed in this solution. How is the solution classified relative to the cell’s initial osmolarity and sustained volume response?

Accepted Answer

Hyperosmotic and isotonic

Question 12

Which best distinguishes receptor-mediated endocytosis from pinocytosis?

Accepted Answer

Receptor-mediated endocytosis binds and concentrates specific cargo before uptake

Question 13

During regulated exocytosis, what event directly releases the vesicle’s contents into the extracellular space?

Accepted Answer

The vesicle fuses with the plasma membrane

Question 14

Two solutes are transported across a membrane in opposite directions by the same protein. What is this transport mechanism called?

Accepted Answer

Antiport

Question 15

In a U-tube experiment, water moves into the side with higher solute concentration until the fluid column rises and net water entry stops. What balances the osmotic driving force?

Accepted Answer

Hydrostatic pressure generated by the fluid column

Question 16

A solution is iso-osmotic to a cell but contains only solutes that freely penetrate the membrane. What is the best conclusion about its effect on cell volume?

Accepted Answer

It may be hypotonic; equal total osmolarity does not guarantee unchanged cell volume

Question 17

If the Na$$ ^+ $$ gradient across an intestinal cell dissipates, what is the most direct consequence for SGLT1-mediated glucose transport?

Accepted Answer

Its ability to drive glucose uptake uphill decreases

Question 18

Which factor does NOT directly affect the rate of simple diffusion across a membrane?

Accepted Answer

The number of carrier proteins

Question 19

A cell is placed in a hypertonic solution. What is the expected effect on cell volume, and what is the term for red blood cell shrinkage?

Accepted Answer

Cell shrinks; the process is called crenation

Membrane Transport: Structure, Mechanisms, and Physiology

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