Plasma membranes

Question 1

What is the purpose of phospholipids in the cell membrane?

Answer 1

Molecules arrange into a player where reads face outward (towards the water) on either side of the membrane.
Centre of bilayer hydrophobic, so water-soluble substances can’t pass through it.

Question 2

What is the purpose of cholesterol in the phospholipid bilayer and where are they found?

Answer 2

Fits between phospholipids; binds to hydrophobic tails to make them closely pack together, restricting movement and making the membrane more rigid. Helps maintain the shape of animals cells, which aren’t supported by other cells.

Question 3

What is the purpose of glycolipids and glycoproteins and where are they found in the phospholipid bilayer?

Answer 3

Exist on surface which allows them to act as receptors. Allows them to bind with certain substances on cell’s surface

Question 4

What is the purpose of integral/intrinsic proteins and where are they found?

Answer 4

Pass through the membrane, some form channels or carriers for water soluble molecules to pass through

Question 5

What is the purpose of extrinsic proteins and where are they found?

Answer 5

Found on surface of membrane; some act as enzymes

Question 6

What is diffusion?

Answer 6

Net movement of particles from an area of higher concentration to an area of lower concentration. Passive process

Question 7

What is simple diffusion?

Answer 7

When molecules directly diffuse through a membrane

Question 8

What is facilitated diffusion?

Answer 8

When particles diffuse through carrier or channel proteins

Question 9

What particles go through facilitated diffusion?

Answer 9

Large molecules that would diffuse very slowly. Charged particles as they’re water soluble.

Question 10

What are carrier proteins?

Answer 10

Move large molecules across membranes, down the concentration gradient.

Question 11

How do carrier proteins work?

Answer 11

1) large molecules attach binding site in carrier protein in the membrane
2) protein changes shape
3) releases molecule on opposite side of membrane

Question 12

What are channel proteins?

Answer 12

Form pores in the membrane for charged particles to diffuse through.

Question 13

What 3 factors affect simple diffusion?

Answer 13

1. Concentration gradient: the higher the CG, the faster the rate of diffusion.
2. Thickness of membrane: the thinner the exchange surface, the faster the rate of diffusion.
3. Surface area: the larger the surface area, the faster the rate of diffusion.

Question 14

What 2 factors affect facilitated diffusion?

Answer 14

1. Concentration gradient: the higher the CG, the faster the rate of facilitated diffusion.
2. No. Of channel/carrier proteins: once all proteins are in use, facilitated diffusion can’t happen faster, even if conc. Is increased.

Question 15

What is osmosis?

Answer 15

Diffusion of water molecules from an area of high water potential to an area of low water potential, across a partially permeable membrane

Question 16

What does isotonic mean?

Answer 16

When two solutions have the same water potential

Question 17

What 3 factors does the rate of osmosis depend on?

Answer 17

1)water potential gradient: the higher the gradient, the faster the rate of osmosis. As osmosis takes place, difference in water potential decreases, leading to a plateau.
2) thickness of exchange surface: the thinner the exchange surface, the faster the rate of osmosis.
3) surface area of exchange surface: the larger the surface area, the faster the rate of osmosis.

Question 18

What is active transport?

Answer 18

When a molecule attaches to a carrier protein, taking it from a high to low concentration using ATP as an energy source.

Question 19

ATP made up of

Answer 19

Adenine, ribose sugar and phosphate groups.

Question 20

When does ATP release energy?

Answer 20

Releases energy when phosphate bonds are broken in a hydrolysis reaction splitting into ADP and pi