Module 1 Lecture 7: Tonicity + Osmolarity & Unassisted and Assisted Membrane Transport

Question 1

What is tonicity?

Answer 1

Effect that a solution has on the volume of the cell

Question 2

What is the tonicity of the solution determined by?

Answer 2

Non-penetrating solutes in the solution

Question 3

What does tonicity do to the volume of a cell?

Answer 3

Either make the volume stay the same, increase or decrease

Question 4

What do the penetrating solutes do in the solution (Tonicity)

Answer 4

Penetrating solutes exchange equally in the ECF and ICF

Question 5

What is isotonic?

Answer 5

When the cell volume stays the same

Question 6

What is hypotonic?

Answer 6

Solution that makes the volume swell in the cell

Question 7

What is hypertonic?

Answer 7

Solution that makes the volume decrease in the cell

Question 8

If we had 300mosm of non penetrating solutes in a beaker and we put a RBC with 300mosm of non-penetrating solute in the intracellular fluid in the beaker what would the tonicity turn out to be?

Answer 8

Isotonic because the non-penetrating solute concentration is equivalent meaning none of them have more water than the other

Question 9

What is Osmolarity?

Answer 9

Measure of solute concentration per unit of solvent (you count both penetrating and non-penetrating solute concentrations)

Question 10

How is osmolarity different from tonicity?

Answer 10

Take into account all solute concentration (you count both penetrating and non-penetrating solute concentrations)

Question 11

What affects the volume of a cell? Tonicity or Osmolarity?

Answer 11

Tonicity (only concentrations of non-penetrating solutes)

Question 12

What is iso-osmotic?

Answer 12

Osmolarity of a solution is equal to the osmolarity of a cell

Question 13

What is hypo-osmotic?

Answer 13

If the osmolarity of the solution is lower than the osmolarity of the cell

Question 14

What is hyper-osmotic?

Answer 14

Osmolarity of the solution is higher than the osmolarity of the cell

Question 15

What is molarity?

Answer 15

Ratio of solvents moles to the entire solution (i.e. 200mmol of NaCl dropped in solution still means 200mmol of that concentration)

Question 16

How do ion forming compound affect osmolarity? Explain using NaCl

Answer 16

With NaCl these compounds can dissolve in solution (like water) and form ions which makes the osmolarity twice the amount because each ion affects the movement of water (osmotic pressure) due to them both being non-penetrating

Question 17

Why is osmolarity>molarity

Answer 17

Molarity takes into account the concentration of that solute (compound) as a whole in terms of the solution it is in.

Osmolarity looks at the total amount of solutes present (individual ionic ions)

Question 18

Can large, poorly lipid soluble molecules passively move through the membrane?

Answer 18

No; requires assisted transport

Question 19

What are the two mechanisms in active transport?

Answer 19

Carrier-mediated transport & Vesicular transport

Question 20

What can carrier proteins do in the membrane when it takes a molecule in or kicks a molecule out?

Answer 20

It can change its shape so that the binding sites face the ICF or ECF

Question 21

What are the three characteristics of carrier mediated transport proteins?

Answer 21

Specificity, Saturation and Competition

Question 22

What does specificity mean in carrier mediated transport?

Answer 22

Binding sites will only expose itself to specific molecules (Glut transporter only takes glucose)

Question 23

What does saturation mean in carrier mediated transport?

Answer 23

A limited number of carrier binding sites

Question 24

What does competition mean in carrier mediated transport?

Answer 24

Closely related compounds compete to get access

Question 25

How does saturation work?

Answer 25

If we have 100 glucose transporters but have 1000 molecules of glucose only 100 of them can go at a time; limited by the number of carrier binding sites

Question 26

What are the two forms of carrier-mediated transport?

Answer 26

Active and passive

Question 27

What is facilitated diffusion?

Answer 27

Uses carrier molecules to assist the transfer of substances across the membrane from high concentration to low concentration

Question 28

Does a carrier-mediated transport need to use energy?

Answer 28

Not necessarily; if it’s something moving from high to low concentration then no need even if it’s a substance that requires the carrier-mediated transport to cross the membrane but in other cases it can use energy

Question 29

Type of diffusion where it’s passive but requires a carrier is?

Answer 29

Facilitated diffusion

Question 30

Passive diffusion is defined as?

Answer 30

Transfer of substance from high concentration to low concentration without assistance of a carrier

Question 31

What is facilitated diffusion rate limited by?

Answer 31

Saturation and Ficks Law

Question 32

Explain how facilitated diffusion would occur with glucose?

Answer 32

1) High concentration of glucose outside the cell can’t pass through the membrane itself so it goes to a carrier-mediated transport protein specific to glucose
2) Carrier in resting state faces the outside of the cell with it’s binding site open to glucose.
3) Once glucose binds to it the carrier protein shifts (confirmational change) from outside the cell
4) Glucose molecule is automatically released because there’s a lower concentration of glucose in the area it’s headed to
5) Once the glucose is gone and the binding site is empty; the carrier flips back to original position to repeat the process

Question 33

How is the rate of diffusion in simple diffusion differ from carrier-mediated transport?

Answer 33

Simple diffusion goes with fick’s law => greater concentration means faster the rate of diffusion

In carrier-mediated, there are things limiting the rate of diffusion, specifically saturation which makes the rate of diffusion, plateau if there is too much that wants to diffuse all at once but there are not enough carriers