(4) Structure Of Cell Membranes

Question 1

What makes up a phospholipid.

Answer 1

Hydrophilic phosphate head
Hydrophobic hydrocarbon tails

Question 2

Phospholipid function:

Answer 2

-Allow lipid-Soluble substances to enter and leave the cell.
-Prevents water soluble substances to enter and leave cell.
-Make the membrane flexible and self-sealing

Question 3

Function of Cholesterol in the cell membrane

Answer 3

-Reduces lateral movement
-Makes the membrane less fluid at high temperatures
- Prevents leakage of water and dissolved ions from cell.

Question 4

Compare the functions and structures of Intrinsic proteins In the cell membrane:

Answer 4

Protein channels:
Are selective
Opens to the presence of a specific water-soluble ions

Carrier proteins:
-Have binding sites for specific chemicals
-When binded causes change to tertiary structure
Which allows chemical to pass through

Question 5

Why is the structure of cell membrane referred to as a Fluid mosaic model?

Answer 5

Fluid: Individual phospholipids can move relative to each other. This makes the membrane flexible.

Mosaic:
Proteins embedded in phospholipid bilayer. Vary in shape, size and pattern.

Question 6

Permeability of the cell surface membrane:
Molecules do not diffuse freely through the membrane if:

Answer 6

-Non lipid soluble
- Too large of a molecule
- Similar/Identical charge to protein channels
-Polar

Question 7

Define diffusion and compare between facilitated and simple diffusion.

Answer 7

-net movement of particles from high to low concentration until evenly distributed.

Both:
Passive
Requires no ATP

Facilitated:
Relies on inbuilt motion(kinetic energy) of the diffusing molecules

Question 8

Osmosis:
State the Definition (1)

How water potential fluctuates when adding a solute to pure water. (2)

What happens when a red blood cell is placed into pure water (3)

Answer 8

(1) net movement of water particles from high water potential to low water potential through a partially permeable membrane.

(2) Adding solute to pure water will lower water potential. Eg. ( 0 to -30kPa)

(3) Red blood cells placed into pure water will absorb water. As the potential is lower inside cell
Cell will burst

Question 9

Describe the Co-Transport and Absorption of glucose into the ileum:

Answer 9

(1) Sodium ions actively transported out of epithelial cells by sodium potassium pump into the blood.

(2) This maintains a higher concentration gradient of sodium ions in the lumen of the intestine than the inside of the epithelial cells

(3) sodium ions diffuse into the epithelial cell down the concentration gradient through a different type of protein carrier. As the sodium ions diffuse, they carry either an amino acid or glucose molecule with them.

(4) glucose/ amino acids pass into blood plasma by facilitated diffusion using another type of carrier.

Question 10

Describe Direct active transport:

Answer 10

Molecule/ion attaches to receptor site of carrier protein.(This occurs on the side of membrane with lower concentration)

Molecule of ATP then binds to carrier protein.

ATP undergoes hydrolysis
producing inorganic phosphate and ADP.

Phosphate attaches to carrier protein causing it to change shape.

Shape change causes carrier protein to transport molecule to other side of membrane.

Phosphate now leaves carrier protein causing it to return to original shape.

ADP and phosphate later reform into ATP during aerobic respiration

Question 11

Factors affecting diffusion.

Answer 11

Temperature
Surface area
Concentration gradient
Size of diffusing molecules