2.5 Membrane Permeability Flashcards
What do membranes control?
The passage of substances in and out of cells
What are the three processes substances move by?
Osmosis
Diffusion
Active transport
What is osmosis?
The diffusion or water molecules across a partially permeable membrane down a water potential gradient
What is diffusion?
The passive movement of molecules from a high to low concentration, down a concentration gradient until equilibrium is reached
What is active transport?
The movement of molecules from a low to high concentration, energy is required as it goes against the concentration gradient
If membrane structure is lost what occurs?
Disruption of cell processes and material entry and exit
What three things affect membrane structure/permeability?
Temperature
Solvent
PH
What is permeability?
The ability of molecules to pass through a membrane
Plasma membranes are semi permeable what does this mean?
Some substances can pass through others cannot
What determined if a substance passes through a oily membrane?
It’s solubility
Give examples of soluble substances that pass straight through the membrane:
Steroid hormones
Oxygen
Carbon dioxide
What substances so not pass through plasma membranes?
Glucose
Proteins
Lipids
Only pass through channel proteins
What increases the fluidity of the membrane?
The unsaturated hydrocarbon tails - they keep the molecules from packing together
What effect does increased temperature have on the membrane?
Phospholipids have more kinetic energy and they move more, making the membrane more fluid so it looses its structure
What does further temperature increase do to the membrane?
Causes the membrane to break down, increasing permeability making it easier for particles to pass through
What effect does further increased temperature have on the proteins in the membrane?
If denatures them, decreasing membrane permeability as molecules like ions require proteins to pass through the membrane
What is water?
A polar solvent essential for the formation of the phospholipid bilayer
What are many organic solvents and what affect do they have on membranes?
Less polar than water
They dissolve membranes, disrupting cells
What effect does surrounding cells in a solvent have on the permeability of the membrane? Why?
Increased permeability
As solvents dissolve lipids in the membrane causing it to loose structure
What effect does increasing solvent concentration have?
Increased permeability
What investigation into temperature’s effect on membrane permeability can be carried out?
Beetroot
What are the steps in the beetroot investigation?
- 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
Why are the pieces of beetroot rinsed in water?
To remove excess pigment
The higher the membrane permeability…
The more pigment released and the higher the absorbance
