Membrane Function

Question 1

Describe the structure of the cell membrane?

Answer 1

• Cell membranes are composed of a phospholipid bilayer with embedded proteins.
  
  • The hydrophilic heads of phospholipids face outward, interacting with the aqueous environment, while the hydrophobic tails are oriented inward.

Question 2

How do substances cross the membrane?

Answer 2

Substances can cross cell membranes through passive processes (no energy required) like diffusion and facilitated diffusion, or active processes (energy required) like active transport.

Question 3

Describe diffusion through aqueous pores

Answer 3

Aqueous pores, formed by channel proteins, allow small, water-soluble molecules to diffuse across the membrane.

This process is selective, as the size and charge of the molecules influence their passage.

Question 4

What type of molecules can dissolve in the lipid bilayer?

Answer 4

Lipid-soluble molecules can dissolve directly in the lipid bilayer, traversing the membrane without the need for specific channels or carriers.

This method is efficient for substances that can easily penetrate lipid membranes.

Question 5

What is facilitated diffusion?

Answer 5

In facilitated diffusion, specific carrier proteins aid the movement of large or polar molecules across the membrane.

This process is passive and follows the concentration gradient.

Question 6

What is active transport?

Answer 6

Active transport requires energy (usually ATP) to move substances against their concentration gradient.

Carrier proteins, often pumps, actively transport ions or molecules, maintaining cellular homeostasis and creating concentration gradients.

Question 7

How does the sodium potassium pump work?

Answer 7

For each cycle of the sodium-potassium pump, it actively transports three sodium ions (Na+) out of the cell and two potassium ions (K+) into the cell, at the same time. This transport process is powered by the hydrolysis of one molecule of ATP (adenosine triphosphate).