Cell Membranes

Question 1

What do membranes do?

Answer 1

Act as a barrier but also are semi permeable so things can pass through.

Question 2

Cell membranes have … , what structure?

Answer 2

Fluid Mosaic Model

Fluid = phospholipids are moving
Mosaic = proteins scattered

Question 3

How are Glycoproteins formed?

Answer 3

When proteins have a carbohydrate chain attached.

Question 4

How are Glycolipids formed?

Answer 4

When lipids are combined with a carbohydrate chain.

Question 5

How are the phospholipid molecules arranged?

Answer 5

Head is hydrophilic so it faces the water.

Tail is hydrophobic so it faces away from the water and also means it is not water soluble.

Question 6

How do the molecules arrange themselves?

Answer 6

Into a bilayer.

Question 7

What do Receptor Proteins on the cell surface membrane do?

Answer 7

Detect chemicals released from other cells which signal a cell to respond in some way.

Question 8

What does Cholesterol do on the cell surface membrane?

What does this do?

Answer 8

It’s between the phospholipids and binds the tails together = more closely.

Restricts their movement - helps to maintain their shape since animal cells don’t have a Cell Wall.

Question 9

Investigate how temperature affects permeability of a beet root membrane: (3)

Answer 9

1) cut 5 equal beetroot’s with a scalpel then rinse, put them in test tubes containing same amount of water.
2) put each tube in water bath 10-50 degrees for same time and remove the beetroot from the tube, leaving liquid.
3) use a colorimeter to measure absorbable. Higher the absorbance, the more pigment and he more permeable be memebrane is.

Question 10

What would a Colorimeter show you about how temperature affects the permeability of a membrane: (3)
Below 0
0-45
Above 45

Answer 10

• below 0 degrees, no energy and no permeable membrane as things can’t move.
• 0-45 degrees, can move and phospholipids have more energy to move = increases permeability.
• above 45 degrees, phospholipid bilayer starts to break down as it becomes even more permeable - Proteins deform so they can’t control what enters . Increases permeability.

Question 11

Why is it bad for the membrane of the temperature is below 0 degrees?

Answer 11

Because channel proteins and carriers may deform and ice crystals may form and pierce the membrane making it highly permeable when it thaws.

Question 12

What is Diffusion?

Answer 12

The net movement of particles from an area of high concentration to an area of a lower concentration until equilibrium.

Question 13

Does Diffusion require energy?

Answer 13

No because it is a PASSIVE process.

Question 14

When would Facilitated Diffusion be used?

Answer 14

When larger molecules need to pass = takes longer.

Charged particles = diffuse slower because they’re water soluble and the tail is hydrophobic.

Question 15

What do Channel Proteins do?

Answer 15

They form pores in the membrane for charged particles to diffuse through - different channel proteins are needed for different charged proteins.

Question 16

What do Carrier Proteins do?

Answer 16

A large molecule attaches to a carrier protein in the membrane, the protein changes shape and releases the large molecule on the opposite side of the membrane.

Question 17

Does Facilitated Diffusion require energy?

Answer 17

No, it’s also a passive process.

Question 18

The rate of simple Diffusion depends on… (3)

Answer 18

• conc gradient, the higher = the faster.
• thickness of exchange surface = the shorter distance, the faster.
• the surface area, the larger the surface area. = the faster.

Question 19

Where do Microvilli work?

Answer 19

On epithelial cells in the small intestine.

Question 20

What do Microvilli do?

Answer 20

They increase the surface area by about 600 times meaning more particles can be exchanged in the same amount of time.

Question 21

The rate of Facilitated Diffusion depends on… (2)

Answer 21

• conc gradient, the higher = the faster.
• number of channel/carrier Proteins = the more of them = the faster but only to a point as there won’t be enough particles.

Question 22

What are Aquaporins?

Answer 22

Channel proteins that allow the Facilitated Diffusion of water throughcell membranes - kidney cells have lots of them.

Question 23

The aquaporins allow…

Answer 23

The cells to reabsorb a lot of the water that would otherwise be excreted by the body.

Question 24

What is Osmosis?

Answer 24

The diffusion of water molecules from an area of a high water potential to an area of lower water potential, across a semi permeable membrane.

Question 25

The rate of Osmosis depends on… (3)

Answer 25

• water potential gradient, the higher = the faster.
• thickness of exchange surface = the thinner = the faster.
• surface area of the exchange surface = the larger = the faster.

Question 26

What does Active Transport do?

Answer 26

It moves solutes from a low to a high concentration - against a concentration gradient.

Question 27

Does Active Transport require energy?

Answer 27

Yes, ATP energy which is produced by respiration.

Question 28

How does ATP provide energy?

Answer 28

It undergoes a hydrolysis reaction, splitting ATP into ADP and P - releases energy.

Question 29

What proteins are involved in Active Transport?

Answer 29

Carrier proteins.

Question 30

Give an example of one type of Carrier protein involved in Active Transport:

Answer 30

Co - Transporters.

Question 31

What do Co-Transporters do?

Answer 31

They bonds two molecules at a time and the conc gradient of one of the molecules is used to move the other molecule against its own conc gradient.

E.g. sodium and glucose.

Question 32

The rate of Active Transport depends on…. (3)

Answer 32

• the speed of carrier proteins, the faster they work = faster reaction.
• number of carrier proteins = more proteins, the faster.
• rate of respiration and the amount of ATP, more energy = faster.

Question 33

Describe how the products of starch (Glucose) is absorbed into the blood from the small intestine: (4)

Answer 33

• sodium is removed from epithelial cells by active transport via the sodium potassium pump into the blood.
• this maintains a low conc of sodium in epithelial cell compared to lumen.
• glucose moves into the blood by facilitated diffusion.
• glucose moves in with the sodium to the epithelial cell via a carrier protein.

Question 34

Solute

Answer 34

Any substance dissolved in a solvent.

Question 35

Solvent

Answer 35

e.g.water

Question 36

Solution

Answer 36

Solute and Solvent together.

Question 37

Units for water potential..

Answer 37

kPa

Question 38

What is the highest value for water potential?

Answer 38

0 - pure water has this.

Question 39

What happens if you add a solute to water and why?

Answer 39

You lower its water potential as the H20 molecules are attracted to the solute so they are less free to move around.

Question 40

Define Osmosis in terms of water potential:

Answer 40

The movement of particles from an area of high water potential to an area of low water potential against a semi-permeable membrane.

Question 41

What happens if an animal cell is put in pure water?

What happens if an animal cell is put in a high sugar conc?

Answer 41

• pure water would make it burst.

- high sugar conc would cause it to shrink and the membrane would wrinkle.

Question 42

Hypotonic..

Answer 42

A solution with a low solute concentration so there are more water particles.

Question 43

Hypertonic..

Answer 43

A solution that contains a high solute concentration and low water potential.