Membranes

Question 1

Equilibrium

Answer 1

When there is no net movement of molecules in one direction

Question 2

Rate of diffusion affected by

Answer 2

Temperature (more Ek, more random movement, faster rate)
Concentration gradient
Stirring/moving molecules
Surface area (more space for molecules to diffuse)
Thickness/ diffusion distance
Size of molecule

Question 3

What sort of matter can use simple diffusion across a membrane

Answer 3

Small (simple) molecules, CO2, H2O

Lipid-based molecules (steroid hormones, oestrogen)

Question 4

What sort of matter can use facilitated diffusion using channel proteins to cross a membrane?

Answer 4

Ions (Na+ or Ca2+)
Polar molecules (water soluble molecules)

Question 5

What sort of matter use facilitated diffusion using carrier proteins to cross a membrane?

Answer 5

Large molecules eg glucose and amino acids

Question 6

Facilitated diffusion

Answer 6

Passive movement of molecules across membranes down their concentration gradients aided by transport proteins (channel/carrier)

Question 7

Channel proteins

Answer 7

Pores in membrane
often shaped to allow only one type of ion through
can be gated (opened or closed)

Question 8

Carrier proteins

Answer 8

Shaped so a specific molecule can fit into them at membrane surface
When it fits, protein changes shape, allows molecule through to other side.
Or use ATP carry specific molecules in opposite direction to concentration gradient
Shape change doesn’t allow molecule back through
Faster than diffusion
Can accumulate molecules inside/ outside cells or organelles

Question 9

How membranes control type of substances entering or leaving cell

Answer 9

Different membranes can have different carrier/channel proteins, so only certain types of substance can pass in or out across membrane

Question 10

Endocytosis and exocytosis

Answer 10

Endocytosis is the formation of vesicles by the plasma membrane, which moves molecules into the cell, using ATP
Exocytosis is fusion of vesicles with the plasma membrane, which moves molecules out of the cell, using ATP

Question 11

Define water potential

Answer 11

A measure of the tendency of water molecules to osmose from one place to another

Question 12

Functions of membranes

Answer 12

Cell surface membrane keeps cell contents separate form surroundings
Limits what molecules can enter and leave cell
Enables cell to communicate with other cells via cell signalling

Organelle membranes compartmentalise the cell
Keep cell processes separate
Enable each process to occur in a specialised area of the cell
Processes don’t interfere
Sets up concentration gradients

Question 13

Parts of the fluid mosaic model

Answer 13

Describes the molecular arrangement of all membranes in a cell

Phospholipid bilayer

Cholesterol regulates fluidity, more stable, holds phospholipid tails together (mechanical stability) makes membrane less permeable to water and other substances eg ions

Glycolipids and glycoproteins cell attachment/ signalling
Proteins within membrane (extrinsic, intrinsic or float freely)

Question 14

What do many medicinal drugs do?

Answer 14

Enhance or inhibit the action of hormones that usually bind to receptors on cell surface membrane

Question 15

Diffusion

Answer 15

Net movement of molecules from a region of high concentration to a region of lower concentration for that molecule down a concentration gradient