lecture 7 - osmosis & membrane potential

Question 1

What is diffusion?

Answer 1

The movement of molecules from high concentration to low concentration

Question 2

What is osmosis?

Answer 2

The movement of water across a semi-permeable membrane to equalize solute concentration

Question 3

How can the flow of water across a semi-permeable membrane be opposed?

Answer 3

By applying force against the direction of flow

Question 4

What divides intracellular and extracellular spaces

Answer 4

semi-permeable membrane

Question 5

What does osmosis balance?

Answer 5

Tonicity

Question 6

What is an isotonic solution in cells?

Answer 6

When the ECF and ICF are in balance, with equal concentration

Question 7

What is a hypertonic solution?

Answer 7

A solution with a higher solute concentration, and less water, so water will flow into the solution

Question 8

What is a hypotonic solution?

Answer 8

A solution with a low solute concentration and high amount of water. Water flows into cell to restore equilibrium

Question 9

If the extracellular fluid is hypotonic, will a cell shrivel or swell?

Answer 9

Swell

Question 10

If the extracellular fluid is hypertonic, will a cell shrivel or swell?

Answer 10

Shrivel

Question 11

What are the two key electrolytes in the body?

Answer 11

NaCl and KCl

Question 12

What are the two key cations in the body?

Answer 12

Na+ and K+

Question 13

Is [Na+] greater inside or outside the cell?

Answer 13

Outside the cell.

Question 14

Is [K+] greater inside or outside the cell?

Answer 14

Inside the cell.

Question 15

How do Na+ and K+ passively move in/out of the intracellular fluid?

Answer 15

Through ion channels in the plasma membrane.

Question 16

What do active sodium and potassium pumps use to provide energy?

Answer 16

ATP, which is converted into ADP, releasing energy.

Question 17

What is the value of the resting membrane potential?

Answer 17

-70mV

Question 18

At rest, which side of the cell membrane is positive and which is negative?

Answer 18

Intracellular fluid is negative, Extracellular fluid is positive.

Question 19

What is the ratio of K+ to Na+ exchanged by the sodium potassium pump?

Answer 19

2 K+, 3 Na+

Question 20

What is an electrical gradient?

Answer 20

The difference in charge between the ICF and ECF, caused by a difference in the concentration of cations on either side of the cell membrane.

Question 21

What direction does the electrical gradient drive cations?

Answer 21

From positive to negative - into the intracellular fluid

Question 22

Why does the electrochemical gradient of K+ push ions weakly?

Answer 22

The electrical gradient opposes the chemical gradient of the Potassium, limiting movement out of the cell.

Question 23

Why does the Na+ electrochemical gradient strongly push Na+ into the cell?

Answer 23

The chemical and electrical gradient are in the same direction, meaning they add to give an electrochemical gradient with a large magnitude.

Question 24

What is depolarization?

Answer 24

When excitable cells trigger ion channels, causing sodium ions to flow into the cell, increasing the membrane potential (the magnitude of the membrane potential decreases, but it becomes more positive so there is a net increase).

Question 25

What is repolarisation?

Answer 25

When a stimulus is removed and excess ions in the cell are removed, decreasing the membrane potential until it reaches the initial membrane potential.

Question 26

What is hyperpolarization

Answer 26

Membrane potential becomes more negative and so K+ channels open and more K+ leave cell