Active cellular physiology

Question 1

Define diffusion

Answer 1

The passive movement of molecules from an area of high to low concentration (along conc. gradient)

Question 2

Define osmosis

Answer 2

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

Question 3

Outline why water moves during osmosis, rather than the solute

Answer 3

Solute can’t pass across semi permeable membrane, so water must move to equalise solute concentration

Question 4

What causes osmotic pressure to increase?

Answer 4

An increase in the concentration gradient

Question 5

Describe osmotic pressure

Answer 5

Osmotic pressure is the pressure or force applied to a system to resist the movement of water

Question 6

Describe an isotonic solution

Answer 6

When the concentration of solute is equal on both sides of a semi permeable membrane

Question 7

Describe an hyPERtonic solution

Answer 7

High concentration of solute outside membrane, causing water to move from ICF to ECF to restore osmotic equilibrium

Question 8

Describe an hyPOtonic solution

Answer 8

Low concentration of solute outside membrane, causing water to move from ECF to ICF to restore osmotic equilibrium

Question 9

Outline why saline or Ringer’s solution is given intravenously to dehydrated patients instead of pure water

Answer 9

When water added to blood stream, conc. of solutes in blood cells cannot change,
therefore blood becomes hypotonic, water moves into blood cells, danger of cells bursting

Question 10

Name 3 of the most common ions in the human body

Answer 10

Na+, K+, Cl-

Question 11

What is an ion gradient?

Answer 11

The imbalanced distribution of charge across a membrane, which can be used to power future work

Question 12

How do ions move down their concentration gradient, and what is required for this to happen?

Answer 12

Move through passive ion channels, not requiring ATP. Ion channel just need to open

Question 13

Describe the sodium-potassium ion pump, including specific ion ratios.

Answer 13

The sodium-potassium ion pump uses ATP energy to push 3 Na+ ions out of cell and 2 K+ ions in, against their conc. gradient. This form of active transport is used to restore concentration gradient of ions across the membrane

Question 14

Describe the relative electrical gradient across the cell membrane

Answer 14

The inside of the cell is relatively negative, because 2 +ves in, 3 -ves out

Question 15

Define ‘resting membrane potential’ and the normal value of this

Answer 15

The electrical gradient DIFFERENCE when the cell is at rest/at balance point. About -70mV

Question 16

Describe the gradients of K+ (electrical, chemical and electrochemical gradients)

Answer 16

• Electrical gradient wants K+ to stay in cell to cancel out negative charge
• Outweighed by chemical gradient of high concentration of K+ inside cell, low outside
  = electrochemical gradient of K+ out of cell is small (difference of the two gradients)

Question 17

Describe the gradients of Na+ (electrical, chemical and electrochemical gradients)

Answer 17

• Electrical gradient wants Na+ to move into cell to cancel out negative charge
• Chemical gradient of high Na+ concentration outside cell, low inside also causes Na+ to move into cell
  = electrochemical gradient of Na+ into cell is large (sum of the two gradients)

Question 18

Name 2 types of ‘excitable’ cells

Answer 18

Nerve and muscle cells

Question 19

What is the function of depolarisation in excitable cells

Answer 19

Nerve and muscle cells use the movement of ions to depolarise the cell in order to send a signal (action potential)

Question 20

Describe the process of depolarisation

Answer 20

A chemical stimulus opens sodium ion channels, Na+ enters cells causing membrane potential to decrease (depolarisation) (~-60 mV)

Question 21

Describe the process of repolarisation

Answer 21

Stimulus removed, excess Na+ pumped out of cell using ATP energy, cell returns to resting membrane potential (repolarisation)