Cell membrane and Osmosis

Question 1

cell membranes are composed primarily of _______ and _______.

Answer 1

phospholipids and proteins

Question 2

how do water-soluble substances (eg. Na+, Cl-, glucose, H2O) that do not dissolve in the lipid membrane cross the lipid bilayer?

Answer 2

they can cross through water-filled channels.

They may also be transported by carriers.

Question 3

what does carrier-mediated transport include?

Answer 3

includes facilitated diffusion and primary and secondary active transport.

Question 4

characteristics of carrier-mediated transport:

Answer 4

1. stereospecificity. a carrier can only transport certain types of substances.
2. Saturation. The transport rate increases as the concentration of the solute increases, until the carriers are saturated.
3. Competition. Structurally related solutes compete for transport sites on carrier molecules.

Question 5

does facilitated diffusion require metabolic energy?

Answer 5

facilitated diffusion does not require metabolic energy. it is passive.

Question 6

examples of facilitated diffusion:

Answer 6

glucose transport in muscle and adipose cells

Question 7

define: isosmotic, hyperosmotic, hyposmotic

Answer 7

Two solutions that have the same calculated osmolarity are isosmotic. If two solutions have different calculated osmolarities, the solution with the higher osmolarity is hyperosmotic and the solution with the lower osmolarity is hyposmotic.

Question 8

osmosis: define

Answer 8

Osmosis is the flow of water across a semipermeable membrane from a solution with low solute concentration to a solution with high solute concentration.

Question 9

reflection coefficient: define

Answer 9

a number between zero and one that describes the ease with which a solute permeates a membrane.
if the reflection coefficient is 1, the solute is impermeable. if the reflection coefficient is 0, the solute is completely permeable.

Question 10

effective osmotic pressure: define

Answer 10

Effective osmotic pressure is the osmotic pressure (calculated by van’t Hoff’s law) multiplied by the reflection coefficient.

Question 11

define: isotonic, hypertonic, hypotonic

Answer 11

Two solutions having the same effective osmotic pressure are isotonic because no water flows across a semipermeable membrane separating them.
If two solutions separated by a semipermeable membrane have different effective osmotic pressures, the solution with the higher effective osmotic pressure is hypertonic and the solution with the lower effective osmotic pressure is hypotonic. Water flows from the hypotonic to the hypertonic solution.