Ch 5

Question 1

What model describes the structure of the cell membrane?

Answer 1

Fluid mosaic model

This model illustrates how membranes are composed of a flexible combination of lipids and proteins.

Question 2

What are the main components of a phospholipid?

Answer 2

2 fatty acid chains, a glycerol molecule, a phosphate group

The fatty acid chains can be either saturated or unsaturated.

Question 3

What is the function of the hydrophilic heads and hydrophobic tails in phospholipids?

Answer 3

Hydrophilic heads face outward; hydrophobic tails point inward

This arrangement forms a bilayer in aqueous environments.

Question 4

What affects membrane fluidity?

Answer 4

Phospholipid type, temperature, cholesterol

Saturated fatty acids pack more closely than unsaturated fatty acids.

Question 5

What are the two types of membrane proteins?

Answer 5

Integral proteins, peripheral proteins

Integral proteins are embedded in the bilayer, while peripheral proteins are attached to the surface.

Question 6

What is the primary function of integral membrane proteins?

Answer 6

Transporters, receptors, enzymes, adhesion

Integral proteins can have hydrophobic and hydrophilic regions.

Question 7

How does simple diffusion occur?

Answer 7

Net movement from high to low concentration

This process does not require a membrane but can occur if the membrane is permeable.

Question 8

What is osmosis?

Answer 8

Diffusion of water across a semipermeable membrane

Water moves from a region of higher concentration to lower concentration.

Question 9

What is the difference between hypotonic, hypertonic, and isotonic solutions?

Answer 9

Hypotonic: cell swells; Hypertonic: cell shrinks; Isotonic: no change

Tonicity depends on the concentration of nonpermeating solutes.

Question 10

What is primary active transport?

Answer 10

Transport that directly uses ATP

Example: sodium-potassium pump.

Question 11

What is secondary active transport?

Answer 11

Transport that uses an electrochemical gradient indirectly

Example: sodium-glucose transporter (SGLT).

Question 12

What creates the resting membrane potential?

Answer 12

Combined effect of ion diffusion, selective permeability, electrical attraction

Typically around -70 mV due to K+ leakage.

Question 13

What is the role of cholesterol in cell membranes?

Answer 13

Maintains membrane fluidity

Cholesterol prevents membranes from becoming too rigid at low temperatures.

Question 14

Fill in the blank: The process of engulfing large particles by the cell membrane is called _______.

Answer 14

Phagocytosis

This process is also referred to as cellular eating.

Question 15

True or False: Exocytosis is the process of exporting substances out of the cell.

Answer 15

True

Involves vesicles fusing with the plasma membrane.

Question 16

What is facilitated diffusion?

Answer 16

Passive transport aided by integral membrane proteins

This process allows polar molecules or ions to diffuse into the cell.

Question 17

What is the function of aquaporins?

Answer 17

Facilitate the movement of water across membranes

They enhance the rate of osmosis.

Question 18

What is osmolarity?

Answer 18

Total osmotic concentration of all solutes in a solution

Important for understanding the movement of water between compartments.

Question 19

What is the difference between channels and carriers in membrane transport?

Answer 19

Channels allow ions/molecules to pass; carriers change shape to transport substances

Channels can be gated or open all the time.

Question 20

What happens during receptor-mediated endocytosis?

Answer 20

Specific substances bind to receptors and are internalized

This process is selective and efficient for certain molecules.

Question 21

What is the role of the sodium-potassium pump?

Answer 21

Maintains concentration gradients of sodium and potassium

Keeps sodium concentration lower and potassium higher inside the cell.

Question 22

What is turgor pressure?

Answer 22

Pressure exerted by the plasma membrane against the cell wall

Important for plant cell stability in hypotonic solutions.

Question 23

Define tonicity.

Answer 23

Ability of a surrounding solution to affect fluid volume and pressure in a cell

It is determined by the concentration of nonpermeating solutes.