Topic 1 - The cell membrane

Question 1

What is Diffusion?

Answer 1

Passive movement of molecules from a high concentration to a low concentration down a concentration gradient

Question 2

What are some factors affecting diffusion?

Answer 2

• Factors WITHOUT membrane = Concentration gradient & Mobility
• Factors WITH membrane = Concentration gradient, membrane permeability, lipid solubility/charge/molecular size & membrane SA/thickness

Question 3

What are the 4 ions and their concentrations inside and outside a cell?

Answer 3

Na+ ions = IN - 10-15mM OUT - 140-160mM
K+ ions = IN - 150mM OUT - 5mM
Cl- ions = IN - 10mM OUT - 100mM
Ca+2 ions = IN - 0.0001 OUT - 1mM

Question 4

How are the concentrations of K+ and Na+ ions maintained in a cell?

Answer 4

• The Na+/K+ pump (ACTIVE TRANSPORT)
• 3:2 respectively for exchange (3Na+ out, 2K+ in)

Question 5

What is membrane potential?

Answer 5

• the potential difference across the membrane due to the uneven distribution of ions between the in and out of the cell
• the inside of the cell is negative in respect to the outside of the cell

*membrane potential is due to a combination of all the ions and their influence in terms of membrane permeability & conc. gradient

Question 6

What is the average membrane potential in cells?

Answer 6

between -60mM to -80mM (use around -70mM)

Question 7

Which channels are voltage-gated?

Answer 7

Sodium, Calcium and Potassium ions

Question 8

What is an action potential?

Answer 8

Is a reversal of membrane potential as a result of change in something.

*characterised by a depolarisation phase then repolarisation phase

Question 9

What are the 3 states channels can be in?

Answer 9

• open
• closed
• inactive

Question 10

What is depolarisation?

Answer 10

It is when the membrane potential becomes more positive*

Question 11

What is hyperpolarisation?

Answer 11

It is when the membrane potential becomes more negative*

Question 12

What is osmolarity?

Answer 12

The concentration of all solute particles (penetrating and non-penetrating)

Question 13

What is Tonicity?

Answer 13

The concentration of non-penetrating solute particles (determines if cells lyse, crenate or remain unaffected)

Question 14

What are the 3 -tonic words and their meaning?

Answer 14

• hypotonic = cells swell & possibly lyse
• hypertonic = cells crenate (shrink)
• isotonic = cells remain unaffected

Question 15

What is the concentration of intracellular fluid?

Answer 15

0.3M/0.30sm/300mOsm