Cell Membraines (Chapter 4)

Question 1

What do membranes do?

Answer 1

Control what passed through them

Question 2

Are membranes partially permeable?

Answer 2

Yes

Question 3

List the three SIMPLE ways substances can move across a membrane?

Answer 3

Osmosis

Diffusion

Active transport

Question 4

What molecules form a continuous bilayer?

Answer 4

Phospholipids

Question 5

Why is the cell membrane model called a fluid mosaic model?

Answer 5

Phospholipids are constantly moving and it looks like a bit like a mosaic

Question 6

What is cholesterols role in the bilayer?

Answer 6

Binds to the phospholipid tails causing them to pack more closely- restricting movement making it more rigid

Helps keep animal cell walls more rigid/ and support eg. Red blood cells

Question 7

What types of proteins are present in the bilayer?

Answer 7

Channel proteins

Carrier proteins

Receptor proteins

Question 8

What are glycoproteins?

Answer 8

Proteins which have a polysaccharide chain attached to it

Question 9

What are glycolipids?

Answer 9

Lipids which have a polysaccharide chain attached to it

Question 10

Can proteins move sideways and also be fixed in position in the bilayer?

Answer 10

Yes

Question 11

In a phospholipid what is the head?

Answer 11

Hydrophilic

Question 12

In a phospholipid what is the tail?

Answer 12

Hydrophobic

Question 13

How is the phospholipid bilayer arranged?

Answer 13

Phospholipid heads face outwards and tails inwards

Centre of the bilayer is hydrophobic- membrane does not allow water soluble substances in

Question 14

Which required practical investigates the permeability of cell membranes?

Answer 14

Beetroot cylinders- pigment leakage

Investigate temperature, concentration etc ………

Question 15

What happens to the permeability of the cell membrane in temperatures below 0°c?

Answer 15

HIGHLY PERMEABLE

Phospholipids do not have much energy so don’t move much
Phospholipids packed closer together

Channel and carrier proteins deform
Ice crystals can pierce membrane

Increases permeability

Question 16

What happens to the permeability of the cell membrane between 0°c & 45°c?

Answer 16

Phospholipids can move around and aren’t tightly packed together

MEMBRANE IS PARTIALLY PERMEABLE

As temperature increases phospholipids move more which increases permeability

Question 17

What happens to the permeability of the membrane at temperatures above 45°c?

Answer 17

Phospholipids start to melt

BECOMES MORE PERMEABLE

Water inside cell expands putting pressure on membrane
Channel and carrier proteins deform- cannot control entry and exit

Question 18

Define diffusion

Answer 18

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.

Question 19

Can molecules diffuse in both directions?

Answer 19

Yes
But the net movement will be to the area of lower concentration. This continues until particles are evenly distributed throughout the liquid or gas.

Question 20

Is diffusion passive?

Answer 20

Yes it does not require metabolic energy

(Requires kinetic energy)

Question 21

What is simple diffusion?

Answer 21

When molecules diffuse directly through a cell membrane

Question 22

What is facilitated diffusion?

Answer 22

Where large or charged molecules, diffuse through carrier or channel proteins in the membrane.

Question 23

Is facilitated diffusion passive?

Answer 23

Yes it does not require metabolic energy

(Requires kinetic energy)

Question 24

What do carrier proteins do?

Answer 24

Move large molecules across membranes

Question 25

How do carrier proteins work?

Answer 25

Large molecule attaches Protein changes shape Releases the molecule on the other side of the

Question 26

What do channel proteins do?

Answer 26

Allows charged particles to diffuse through the membrane

Question 27

What are the three factors that affect the rate of simple diffusion.

Answer 27

The concentration gradient Thickness of the exchange surface The surface area

Question 28

How do microvilli increase the surface area for faster diffusion?

Answer 28

Large surface area- can increase it by 600 times

Question 29

What are the two factors that affect the rate of facilitated diffusion?

Answer 29

Concentration gradient Number of channel or carrier proteins

Question 30

Define osmosis

Answer 30

Osmosis is the diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential

Question 31

What is water potential?

Answer 31

Water potential is the likelihood of water molecules to diffuse in and out of a solution

Question 32

Does pure water have a high water potential?

Answer 32

Yes the highest All solutions have a lower one than water

Question 33

Define isotonic

Answer 33

When two solutions have the same water potential

Question 34

List the three factors which effect the rate of osmosis

Answer 34

Water potential gradient Thickness of exchange surface Surface area of the exchange surface

Question 35

What is the required practical linked to water potential.

Answer 35

Using potato cylinders 5 serial dilutions using sucrose and water Measure mass change %

Question 36

What is active transport?

Answer 36

Active transport uses energy to move molecules and ions across membranes usually against a concentration gradient

Question 37

Which protein is usually involved in active transport?

Answer 37

Carrier proteins

Question 38

What are the two main differences between active transport and facilitated diffusion?

Answer 38

Active transport usually moves molecules form a low to high concentration, in facilitated diffusion they move from a high to low concentration Active transport requires metabolic energy (ATP) facilitated diffusion does not

Question 39

How does ATP release energy?

Answer 39

Undergoes hydrolysis splitting it into ADP and Pi (inorganic phosphate) This releases energy

Question 40

What is a co-transporter?

Answer 40

A type of carrier proteins which binds to two molecules at a time

Question 41

How does co transport work?

Answer 41

Concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient

Question 42

Explain the 4 steps of co-transport of glucose in the ileum of the small intestine?

Answer 42

Sodium ions actively transported out of the epithelial cell into the blood via sodium-potassium pump, this creates a concentration gradient of sodium ions. This causes sodium ions to diffuse from the lumen of ileum into epithelial cell, down their concentration gradient. Via sodium-glucose co-transporter proteins. The co-transporter carries glucose into the cell with sodium- glucose concentration inside cell increases. Glucose diffuses out of the cell into the blood, down its concentration gradient through a protein channel via facilitated diffusion .