Cells (TRANSPORT ACROSS CELL MEMBRANES)

Question 1

What is a phospholipids bilayer made up of

Answer 1

Hydrophilic (water loving) heads facing outwards
Hydrophobic tails ( repel water) facing inwards

Question 2

Describe what the fluid mosaic model of the cell membrane is made up of

Answer 2

Phospholipid bilayer
Cholesterol
Intrinsic protein (spans the whole length of the membrane)
Channel proteins
Carrier proteins
Extrinsic protein (spans halfway through membrane)
Glycolipid (attached to head)
Glycoprotein (attached to a protein)

Question 3

What does cholesterol due to the cell membrane

Answer 3

More cholesterol present makes the membrane less fluid and more rigid
—> this prevents the water leaking out of the cell

Question 4

Define simple diffusion + Give the features of simple diffusion and the molecules it transports

Answer 4

Movement of molecules through the bilayer from a region of high concentration to low concentration (down the concentration gradient)
–> Passive process so does not require ATP
Transports:
–> lipid soluble molecules
–> non polar molecules (not soluble in water)
–> small molecules

Question 5

Define facilitated diffusion + give the features of facilitated diffusion and the molecules it transports

Answer 5

Movement of molecules through the bilayer from a region of high concentration to low concentration (down the concentration gradient) with the use of either a channel protein or carrier protein
–> Passive process so does not require ATP
Transports:
–> polar molecules
–> charged molecules (ions)
–> water soluble molecules

Question 6

Define osmosis

Answer 6

The movement of water molecules from an area of high water potential to an area to low water potential through a partially permeable membrane.
–> Passive process so does not require ATP

Question 7

Define active transport

Answer 7

Movement of all types of molecules through CARRIER protein from an area of low concentration to an area of high concentration.
–> requires energy in the form of ATP

Question 8

Describe how a carrier protein works

Answer 8

The molecule binds to complimentary receptor on the carrier protein
ATP binds to carrier protein and is hydrolysed into ADP + Pi
This causes carrier protein to change shape as the tertiary structure is altered so molecule is released on other side

Question 9

Describe the co trasport of glucose and sodium ions
NOTE: co transport is a type of active transport

Answer 9

1) Sodium ions are actively transported out of the epithelial cell into the blood by the sodium potassium pump
2) This results in a high concentration of sodium outside epithelial cell and lower concentration inside the epithelial cell. This causes sodium ions from the lumen to diffuse from lumen into epithelial cell WITH a glucose molecule by co transporter carrier proteins. Glucose molecule MOVES AGAINST CONCENTRATION GRADIENT
3) Glucose diffuses out of the epithelial cell into blood through protein channel by facilitated diffusion