2.5 Membrane Permeability

Question 1

What do membranes control?

Answer 1

The passage of substances in and out of cells

Question 2

What are the three processes substances move by?

Answer 2

Osmosis
Diffusion
Active transport

Question 3

What is osmosis?

Answer 3

The diffusion or water molecules across a partially permeable membrane down a water potential gradient

Question 4

What is diffusion?

Answer 4

The passive movement of molecules from a high to low concentration, down a concentration gradient until equilibrium is reached

Question 5

What is active transport?

Answer 5

The movement of molecules from a low to high concentration, energy is required as it goes against the concentration gradient

Question 6

If membrane structure is lost what occurs?

Answer 6

Disruption of cell processes and material entry and exit

Question 7

What three things affect membrane structure/permeability?

Answer 7

Temperature
Solvent
PH

Question 8

What is permeability?

Answer 8

The ability of molecules to pass through a membrane

Question 9

Plasma membranes are semi permeable what does this mean?

Answer 9

Some substances can pass through others cannot

Question 10

What determined if a substance passes through a oily membrane?

Answer 10

It’s solubility

Question 11

Give examples of soluble substances that pass straight through the membrane:

Answer 11

Steroid hormones
Oxygen
Carbon dioxide

Question 12

What substances so not pass through plasma membranes?

Answer 12

Glucose
Proteins
Lipids
Only pass through channel proteins

Question 13

What increases the fluidity of the membrane?

Answer 13

The unsaturated hydrocarbon tails - they keep the molecules from packing together

Question 14

What effect does increased temperature have on the membrane?

Answer 14

Phospholipids have more kinetic energy and they move more, making the membrane more fluid so it looses its structure

Question 15

What does further temperature increase do to the membrane?

Answer 15

Causes the membrane to break down, increasing permeability making it easier for particles to pass through

Question 16

What effect does further increased temperature have on the proteins in the membrane?

Answer 16

If denatures them, decreasing membrane permeability as molecules like ions require proteins to pass through the membrane

Question 17

What is water?

Answer 17

A polar solvent essential for the formation of the phospholipid bilayer

Question 18

What are many organic solvents and what affect do they have on membranes?

Answer 18

Less polar than water

They dissolve membranes, disrupting cells

Question 19

What effect does surrounding cells in a solvent have on the permeability of the membrane? Why?

Answer 19

Increased permeability

As solvents dissolve lipids in the membrane causing it to loose structure

Question 20

What effect does increasing solvent concentration have?

Answer 20

Increased permeability

Question 21

What investigation into temperature’s effect on membrane permeability can be carried out?

Answer 21

Beetroot

Question 22

What are the steps in the beetroot investigation?

Answer 22

• cut 5 equal pieces of beetroot
• rinse in water
• place each in different test tube with 5cm of water
• test tubes in different water baths at different temp (e.g 20,30,40,50,60)
• allow pigment to leave
• remove beetroot
• use colourimiter to measure absorbance

Question 23

Why are the pieces of beetroot rinsed in water?

Answer 23

To remove excess pigment

Question 24

The higher the membrane permeability…

Answer 24

The more pigment released and the higher the absorbance