2.5 Cell Membranes

Question 1

What is the structure of cell membranes?

Answer 1

Made of phospholipid bilayer and has hydrophilic heads and hydrophobic tails. (Fluid Mosaic Model)
Also cholesterol, proteins, glycolipids and glycoproteins

Question 2

What is the function of a cell membrane?

Answer 2

It provides a partially permeable barrier that controls what enters and leaves the cell.
It is also involved in cell signalling.

Question 3

What is the role of Cholesterol in cell membranes?

Answer 3

Provides stability.

Question 4

Where would you find Cholesterol?

Answer 4

Binded to tails of phospholipids (in between them)

Question 5

What is the role of channel proteins ?

Answer 5

Allow small ions + polar molecules to diffuse through.

Question 6

What is the role of carrier proteins?

Answer 6

Allow larger molecules in and out of membrane down a conc gradient by diffusion. clasp around it.

Question 7

What are the factors effecting permeability?

Answer 7

1. solvents
2. temperature

Question 8

How do solvents effect permeability of membranes?

Answer 8

Can dissolve lipids in phospholipid bilayer so if you increase con of solvent = increased membrane permeability.

Question 9

Describe diffusion.

Answer 9

Diffusion is the net movement of particles from an area of high concentration to an area of low concentration down a conc gradient. It’s passive so no energy is needed
Molecules do have to be small and lipid soluble.

Question 10

What effects the rate of diffusion?

Answer 10

Temperature, Surface area, Concentration gradient, Thickness of exchange surface.

Question 11

What is facilitated diffusion?

Answer 11

Diffusion that uses carrier and channel proteins to diffuse larger and polar molecules quickly. Still down conc gradient and still no energy required.

Question 12

What is active transport?

Answer 12

Uses energy to move molecules and ions across a plasma membrane against its concentration gradient.
Uses carrier proteins and needs ATP.

Question 13

What is endocytosis?

Answer 13

Molecules that are too large to go through the membrane via carrier proteins get put into vesicles so they can enter (endo=enter as en)
Active process so needs ATP.

Question 14

What is exocytosis?

Answer 14

Vesicles move towards the membrane and fuse with it releasing the content. Exit Exo. Needs ATP to move vesicle along the cytoskeleton.

Question 15

What is osmosis?

Answer 15

The net movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane.

Question 16

What happens to a cell in an isotonic solution and why?

Answer 16

Stays same as water potential is same in and out of cell

Question 17

What happens to a cell in a hypotonic solution?

Answer 17

Cell bursts as water potential in cell is lower so water moves in causing them to swell and become turgid.

Question 18

What happens to a cell in a hypertonic solution?

Answer 18

Cell shrinks due to the solution having a lower water potential and therefore water moves out of cell into surrounding solution. Cell becomes flaccid

Question 19

What is the water potential of pure water?

Answer 19

0

Question 20

How are membranes involved in cell signaling?

Answer 20

They have receptors on their surface and when a messenger molecule binds to them it triggers a change in the cell.

Question 21

What is on the cell membrane allowing for cell signalling?

Answer 21

Receptor proteins called ‘membrane bound receptors’