Tutorial - Week 1 Content

Question 1

Which of the following elements would you NOT expect to find in the plasma membrane of most cells?

a) A double layer of phospholipids
b) Membrane-spanning protein that form channels
c) Membrane protein that that act as receptors
d) Phospholipids with hydrophilic tails
e) Membrane proteins involved in solute pumping

Answer 1

d) Phospholipids with hydrophilic tails (because they are hydrophobic tails)

Question 2

Why are fatty acids able to rapidly move across the plasma membrane?

a) they are they small molecules so can easily move through protein channels

b) they are able to dissolve in the phospholipids of the lipid bilayer

c) they bond to a carrier protein the protein undergoes a conformational change

d) they have a very high thermal energy so a high rate of diffusion

e) they have a low lipid solubility

Answer 2

b) they are able to dissolve in the phospholipids of the lipid bilayer

Question 3

Macromolecules such as hormones and neurotransmitters that are synthesised by cells can be secreted into the extracellular space by which of the following processes?

a) phagocytosis
b) receptor-mediated endocytosis
c) pinocytosis
d) solute pumping
e) none of the above

Answer 3

e) none of the above

(Pinocytosis is the ingestion of liquid into a cell by the budding of small vesicles from the cell membrane)

Question 4

Which of the following substances can cross cell membrane by solute pumping?

1. Na+
2. K+
3. H2O
4. Ca2+

a) 1 and 2 only
b) 2, 3, and 4 only
c) 3 only
d) 1, 2 and 4 only
e) 1, 2, 3 and 4

Answer 4

d) 1, 2, and 4

(Key word is SOLUTE, H2O is a solvent technically)

Question 5

What is the fundamental difference between the diffusion of solutes and the diffusion of water?

a) only water moves against its concentration gradient
b) only solutes move down their concentration gradient
c) the diffusion of water results in changes in volume
d) there is a change in volume following diffusion of solutes
e) there is no difference between the diffusion of solutes and the diffusion of water

Answer 5

c) the diffusion of water results in changes in volume

Question 6

Answer 6

Question 7

Describe an experiment that you could perform to determine whether a substance moved across a cell membrane by facilitated diffusion or simple diffusion?

Answer 7

In order to determine whether a substance moved across the plasma membrane by simple or facilitated diffusion you could perform an experiment where you measured the rate at which the solute moved across the plasma the membrane varied. Because the rate of diffusion is directly proportional to the concentration gradient you would expect to see an increase in the rate of solute transport as the concentration of the solute increases. However because facilitated diffusion requires the solute to bind a carrier protein the rate of solute transport will plateau once all the carrier proteins are saturated. Because simple diffusion does not require a carrier protein the rate of solute will continue to increase.