Question 1

Which of the following best describes the 'fluid mosaic model' of the plasma membrane?

Accepted Answer

A dynamic bilayer of phospholipids with diverse proteins embedded and moving within it.

Question 2

A red blood cell is placed in a solution containing 2% NaCl. The cell's cytoplasm contains 0.9% NaCl. Assuming the membrane is impermeable to NaCl but permeable to water, what will happen to the cell and why?

Accepted Answer

Water will move out of the cell, causing it to shrink, because the solution is hypertonic.

Question 3

Which of the following molecules is most likely to diffuse directly through the phospholipid bilayer of a cell membrane without the aid of a transport protein?

Accepted Answer

Oxygen ($O_2$)

Question 4

Which statement about selective permeability is correct?

Accepted Answer

The plasma membrane allows some substances to cross more easily than others.

Question 5

A cell uses ATP to move potassium ions ($K^+$) into the cell against their concentration gradient. Which type of transport is this?

Accepted Answer

Active transport

Question 6

Which of the following best explains why phospholipids spontaneously form bilayers in water?

Accepted Answer

Their hydrophobic tails avoid water while hydrophilic heads interact with water.

Question 7

A plant cell is placed in pure water. What will happen to the cell, and what is the underlying process?

Accepted Answer

Water will enter the cell by osmosis, causing it to become turgid.

Question 8

Which of the following is an example of receptor-mediated endocytosis?

Accepted Answer

A cell taking in cholesterol by binding it to specific membrane receptors.

Question 9

Which of the following best describes the role of aquaporins in the cell membrane?

Accepted Answer

They allow rapid facilitated diffusion of water across the membrane.

Question 10

A scientist observes that a certain molecule can cross the cell membrane only when a specific protein is present, and this process does not require energy. Which transport mechanism is being observed?

Accepted Answer

Facilitated diffusion

Question 11

Which of the following scenarios best illustrates exocytosis?

Accepted Answer

A vesicle containing neurotransmitters fuses with the plasma membrane to release its contents outside the cell.

Question 12

Which of the following is NOT a function of membrane proteins?

Accepted Answer

Storing genetic information.

Question 13

If a cell is placed in a solution and water moves into the cell, what can you conclude about the tonicity of the solution relative to the cell?

Accepted Answer

The solution is hypotonic to the cell.

Question 14

Which of the following best explains why ions such as $Na^+$ and $Cl^-$ cannot easily cross the phospholipid bilayer?

Accepted Answer

They are repelled by the hydrophobic core of the bilayer.

Question 15

A cell needs to import a large quantity of glucose, which is polar and cannot diffuse directly through the membrane. Which process is most likely used?

Accepted Answer

Facilitated diffusion via a transport protein

Question 16

Which of the following equations correctly represents the movement of water during osmosis?

Accepted Answer

$Water: High \rightarrow Low$ concentration$

Question 17

Which of the following is a real-world example of active transport in human physiology?

Accepted Answer

The sodium-potassium pump moving $Na^+$ out and $K^+$ into nerve cells using ATP.

Question 18

Which process is responsible for a white blood cell engulfing a bacterium?

Accepted Answer

Phagocytosis

Question 19

A mutation causes a cell to lack functional attachment proteins. Which of the following is a likely consequence?

Accepted Answer

The cell cannot attach to the extracellular matrix or cytoskeleton, affecting its structure and signaling.

Question 20

Which of the following best describes the evolutionary significance of membrane formation in the origin of life?

Accepted Answer

Membranes enabled the compartmentalization of molecules, a critical step in the evolution of the first cells.

Cell Membrane Structure and Transport Mechanisms

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