Topic 2B: Cell Membranes

Question 1

What is the definition of diffusion?

Answer 1

Net movement of particles from an area of high concentration to an area of low concentration.

Question 2

What type of process is diffusion?

Answer 2

Passive process, no energy needed

Question 3

When does diffusion stop?

Answer 3

When an equlibrium is reached

Question 4

What 3 things affect diffusion- explain?

Answer 4

Concentration gradient- Higher means its faster
Thickness of exchange surface- Thinner means faster
Surface area- Larger means faster

Question 5

Why is facilitated diffusion needed?

Answer 5

Some larger molecules would diffuse extremely slowly through the phospholipid bilayer as they are so big

Question 6

What do the large/charged particles diffuse through in facilitated diffusion?

Answer 6

Carrier or channel proteins

Question 7

What type of process is facilitated diffusion?

Answer 7

Passive process, no energy needed

Question 8

How does a carrier protein work?

Answer 8

First a large molecule attatches to carrier proteins and the protein changes shape, this releases molecules on opposite side

Question 9

Where do channel proteins form?

Answer 9

In pores

Question 10

What are the 2 things that affect facilitated diffusion?

Answer 10

Concentration gradient- Increased faster until equlibrium reached
Number of proteins- Once all proteins are used, FD can’t occur any quicker even with increased conc gradient

Question 11

How do you work out gradient from a graph?

Answer 11

Change in y/change in x

Question 12

What the definition of osmosis?

Answer 12

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

Question 13

What is the definition of water potential?

Answer 13

Potential of water molecules to diffuse in/out a solution

Question 14

What’s the water potential of water?

Answer 14

Zero (0)

Question 15

What’s meant by isotonic?

Answer 15

2 Solutions with the same water potential

Question 16

What’s meant by hypotonic?

Answer 16

Solutions with higher water potential compared with inside cell

Question 17

What’s meant by hypertonic?

Answer 17

Solutions with lower water potential compared with inside cell

Question 18

What 3 factors affect osmosis?

Answer 18

Water potential (Increased WP)
Thickness of exchange surface (Thinner=faster)
Surface area (Increased SA=faster)

Question 19

Is energy needed for active transports?

Answer 19

Energy is needed

Question 20

Whats the definition of active transport?

Answer 20

Net movement of particles from an area of low concentration to an higher concentration

Question 21

What protein is needed for active transport, how does it work?

Answer 21

Carrier protein, molecules attatches to carrier proteins, it changes moving the molecules across the membrane

Question 22

What type of protein are co-transports?

Answer 22

Carrier protein

Question 23

How do co-transporters work?

Answer 23

But they bind 2 molecules at a time, the conc gradient of one is used to transport the other, gradient their conc gradient

Question 24

How do co-transporters work to move glucose into the blood? (step one)

Answer 24

Sodium ions are actively transported out of the epithelial cells in the ileum into the blood sodium-potassium pump creating the conc gradient of Na

Question 25

What’s step 2+3 of the process of glucose being transported into the blood via co-transporters?

Answer 25

This cause sodium ions to diffuse from the lumen of the ileum into the cells. Down the conc gradient via sodium glucose co-transporter proteins
Glucose diffues out of the cell, into the blood through a protein channel by FD

Question 26

What 3 things affect active transport?

Answer 26

Speed of individual carrier protein (Faster= Faster Rate of AT)
Rate of respiration (If respiration inhibited AT doesn’t occur)
Numbers of carrier proteins (More= Faster)

Question 27

How permeable is a cell membrane?

Answer 27

Partially permeable

Question 28

What model best describes cell membranes and when was it created?

Answer 28

Fluid mosaic model (1972)

Question 29

Why is the bilayer ‘fluid’?

Answer 29

Constantly moving

Question 30

What is it called when a carb is attached to a protein?

Answer 30

Glycoprotein

Question 31

Which part of the phospholipid is hydrophobic?

Answer 31

Tail, repels water

Question 32

What part of the phospholipid is hydrophilic?

Answer 32

Head, attracts water

Question 33

What does cholesterol give to a membrane and how?

Answer 33

Stability, fits into hydrophobic tails and packs them closely together restricting movement and makes them less fluid and more rigid

Question 34

Whats another characteristic of cholesterol?

Answer 34

Also has hydrophobic regions so its able to create a further barrier to polar substances moving through the membrane

Question 35

How does the cell membrane act at 0 degrees?

Answer 35

Phospholipids don’t have much energy, so they can’t move very much.
They’re packed closely together and membrane is rigid
Channel and carrier proteins in the membrane denature increasing permeability of the membrane

Question 36

How does the cell membrane act above 45 degrees?

Answer 36

Phospholipid starts to melt and the membrane becomes more permeable.
Water inside the cell expands, putting pressure on the membrane.
Protein denature so can’t control what enters or leaves

Question 37

How does the cell membrane act between 0-45 degrees?

Answer 37

Phospholipids can move around aren’t packed as tightly together, membrane is partially permeable
As the temp increases they move more increasing permeabilty