Cell Membranes

Question 1

What does it mean by partially permeable

Answer 1

Allows some molecules to enter/exit but not all

Question 2

Why is the phospholipid bilayer fluid mosaic

Answer 2

Phospholipids constantly moving
Cholesterol, transport and receptor proteins scattered through phospholipids
Some proteins can move sideways
Proteins to polysaccharides = glycoproteins
Lipids attached to lipid = glycolipids

Question 3

Why does the bilayer not allow polar substances through

Answer 3

Polar molecules are water soluble

And the fatty acid tails are hydrophobic so repel water

Question 4

What is the function of cholesterol in the cell membrane

Answer 4

Helps maintain shape of cells of animal cells without - especially red blood cells not supported by other cells

Question 5

How does cholesterol work

Answer 5

Fits between phospholipids by binding to the fatty acid tails
Making phospholipids pack more closely together
Restricting the movement = more rigid

Question 6

What is the permeability like at 0 and why

Answer 6

Highly permeable

Phospholipids don’t have much energy = packed closely together = rigid
Channel proteins and carrier proteins deform = allow anything through
Ice crystals pierce membrane leaving holes when it thaws

Question 7

What is the permeability at 0-45 and why

Answer 7

Partially permeable

Phospholipids aren’t packed as close together
And have more energy so move more

Question 8

What is the permeability like at 45+ and why

Answer 8

Highly permeable

Bilayer breaks down
Water inside cell expands putting p on memebran s
Channel and carrier proteins deform

Question 9

Is facilitated diffusion passive

Answer 9

Yes

Question 10

Why do large molecules need transport proteins

Answer 10

Too large

Question 11

What type of protein do large molecules use

Answer 11

Carrier proteins

Question 12

What type of protein do polar molecules use

Answer 12

Channel proteins

Question 13

How do carrier proteins work

Answer 13

1. Large molecule attatches
2. Protein changes shape releasing the molecule on the other side
   Down conc grad

Question 14

How do channel proteins work

Answer 14

Pores for charged particles of move through down conc grad

Question 15

What are 3 factors affecting simple diffusion

Answer 15

Conc grad
Thickness of exchange surface
Surface area

Question 16

How does conc grad affect simple diffusion

Answer 16

High cg = higher rate

As diffusion happens the cg decreases until uqm reached (both sides the same concentration) so diffusion slows over time

Question 17

How does thickness affect simple diffusion

Answer 17

Thin = rate increases

Shorter diffusion pathway

Question 18

How does sa affect simple diffusion

Answer 18

Increase sa = rate

More particles can be exchanged in the same amount of time

Question 19

How does microvilli increase rate of diffusion in small intestine

Answer 19

Microvilli = projections of plasma membrane folding up on itself
Increases sa

Question 20

What are 2 things that facilitated diffusion depend on

Answer 20

Conc grad

No of transport proteins

Question 21

How does no of transport proteins affect rate of facilitated diffusion

Answer 21

If all proteins are being used then no more can get through even in conc grad increases

Question 22

How has the kidney adapted for more facilitée diffusion

Answer 22

Lots of aquaporins (water channel proteins) to speed of water réabsorption

Question 23

If a solution has a high water potential what does that mean

Answer 23

High water conc

Low solute conc

Question 24

What 3 things does osomosis rats dépend on

Answer 24

Water potential gradient
Thickness of exchange surface
Surface area

Question 25

What proteins are used in active transport

Answer 25

Carrier

Question 26

What direction do molecules move in active transport

Answer 26

From low conc to high

Question 27

What does actual transport need

Answer 27

Energy (from atp hydrolysis)

Question 28

What is co transport

Answer 28

Bind to 2 molecules At once

Use the conc grad of one molecule to transport the other against theirs

Question 29

What 3 factors affect the rate of active transport

Answer 29

Speed of carrier proteins
Number of carrier proteins
Rate of respiration/availability of atp

Question 30

Why is co transport needed In the ileum

Answer 30

The conc of glucose is too low to diffuse down its conc grad by diffusion