Homeostasis & Resting Potential

Question 1

What is the internal environment of an animal that cells are bathed in?

Answer 1

Extracellular fluid

Question 2

Why carry out homeostasis?

Answer 2

Protect cells from changing external environment

Question 3

‘Constancy of the internal environment is the condition of free life’ - ?

Answer 3

Claude Bernard 1872

Question 4

What is the composition of extracellular fluid?

Answer 4

1/5 blood plasma

4/5 interstitial fluid

Question 5

What does homeostasis mean?

Answer 5

Maintaining the internal environment of an organism different from the external

Question 6

Who invented the name ‘homeostasis’?

Answer 6

Walter Cannon

Question 7

What is the lipid bi-layer membrane a barrier for?

Answer 7

Water, ions, sugars

Question 8

Is there a difference between the environments inside (cytoplasm) and outside the cell?

Answer 8

Yes, inside the cell is maintained ideal for biological molecules to work

Question 9

What is the electrical voltage difference between the inside and outside called?

Answer 9

Resting membrane potential

Question 10

What is ‘the cells electrical battery’?

Answer 10

The resting potential

Question 11

What is the value for the resting potential?

Answer 11

-60 to -80 mV

The inside is 60-80mV negative to the outside

Question 12

What can the resting potential be used for?

Answer 12

Make electrical signals

Movement across membrane

Question 13

How is the resting potential measured?

Answer 13

Intracellular microelectrodes:

Measure the voltage difference between inside and outside an axon, amplify it

Question 14

What are the 2 cell membrane proteins responsible for the resting potential?

Answer 14

Sodium-potassium exchange pump

Potassium ion channel

Question 15

Sodium-potassium exchange pump: what does it do and how?

Answer 15

Expels Na+; imports K+ (3:2 ratio)
Using ATP
So conc of K+ is greater inside the cell

Question 16

Potassium ion channel: what does it do?

Answer 16

Contains a gate
If gate is open, potassium moves through by diffusion
Direction of diffusion depends upon the electrochemical gradient across membrane

Question 17

Who created equation for calculating K+ equilibrium potential?

Answer 17

Nernst (Nernst equation)

Question 18

Who conducted experiment on frog muscle cells and what did they find?

Answer 18

Hodgkin & Horowicz (1959)

Varying external K+ conc alters membrane potential as predicted by Ernst

Question 19

What causes the large voltage difference if only a bit more Na+ is being removed than K+ being pumped in?

Answer 19

K+ moves down its conc gradient out of the cell, increasing voltage difference

Question 20

What is the equilibrium potential for K+

Answer 20

When the voltage difference balances the concentration difference