6. Continued Lipids, Cell Membranes & transport across cell membranes

Question 1

q21 Explain, with reference to Fig 2.2, whether the PAP extracted from M. charantia is a PAP1 or a PAP2 enzyme 2

Answer 1

It is PAP2, because at 0.0 Mg^2+, the enzyme activity is already at 30.

The enzyme activity also barely increases with an increased concentration of Mg^2+

Question 2

With reference to Fig 2.3, describe & explain the effect of increasing phosphatide concentration on PAP activity 3

Answer 2

The activity of PAP increases as phosphatide concentration increases.

The PAP activity increases steadily at first, but slows down at higher phosphatide concentrations

as phosphatide no longer becomes the limiting factor and more active sites are occupied.

Question 3

Explain why phospholipids are able to form a bilayer in cell membranes 2

Answer 3

They have hydrophilic heads with, hydrophobic tails.

They are then able to form a bilayer with hydrophilic heads pointing out into liquid and hydrophobic tails pointing inwards

Question 4

q22 Name structure P

Answer 4

Channel protein

Question 5

q22 Name structure Q

Answer 5

Glycoprotein

Question 6

q22 Name structure R

Answer 6

Cholesterol

Question 7

q22 Name structure W

Answer 7

Phospholipid bilayer

Question 8

q22 State the function of channel proteins

Answer 8

To provide a channel across the membrane for polar ions & molecules to pass through

Question 9

q22 State the function of glycoproteins

Answer 9

Allows cells to recognise each other & initiate immune responses

Question 10

q22 State the function of cholesterol 3

Answer 10

Provides stability and maintains fluidity of the cell membrane

Prevents phospholipids being tightly packed

Serves as myelin sheath in nerve cells

Question 11

q22 State the function of phospholipids 2

Answer 11

Main component of cell surface membrane

controls what enters and leaves the cell

Question 12

Explain what is meant by fluid mosaic 3

Answer 12

Cell membrane is a collection of different structures that resembles a mosaic

proteins and phospholipids can move about by diffusion, causing fluidity

Question 13

Describe how phospholipid molecules are arranged in a cell surface membrane 2

Answer 13

Non-polar, hydrophobic tails face inwards, creating a hydrophobic channel

while polar, hydrophilic heads face outwards

Question 14

State 2 ways in which phospholipids differ from triglycerides 2

Answer 14

triglycerides have 3 fatty acid tails whole phospholipids have 2

phospholipid tails are different lengths while triglyceride tails are all the same length

Question 15

Explain how the structure of triglycerides makes them more suitable for energy storage than carbohydrates 2

Answer 15

They have long hydrocarbon chains that have lots of C-H bonds, which release a lot of energy when broken

The same mass of triglycerides will then give more energy than carbs

Question 16

Name the type of membrane protein to which the cell signalling molecules bind

Answer 16

Cell surface receptors

Question 17

q24 a) The Visking tubing used by the student wasn’t permeable to sucrose. Explain the results shown in table 3.1 3

Answer 17

At sucrose concentrations less than 0.8 mol dm^-3 inside Visking tubing, the water potential is higher inside but lower outside

So water flows down the concentration gradient outside of the tubing

At sucrose concentrations higher than 0.9 mol dm^-3, the water potential is lower inside the tubing

So water outside goes down the concentration gradient into the tubing

and meniscus height increases

Question 18

24 b)Describe and explain the effects on red blood cells of immersion in different concentrations of sodium chloride as shown in Fig 3.2 5

Answer 18

At concentrations less than 0.04 mol dm^-3, all the cells burst

This is because water moves down the water potential gradient, causing the internal volume of the cell to increase

The cell membranes are not strong enough to withstand the pressure and so they burst

At concentrations between 0.04 and 0.14 mol dm^-3, fewer cells are bursting as the water potential gradient is decreasing in steepness

Above 0.14 mol cm^-3, no cells burst. This could be because water is moving out of the cells.

Question 19

q20 in which direction will the water move?

Answer 19

From cell x to both cells Y and z

Question 20

q19 What is 4 showing

Answer 20

diffusion of K+

Question 21

q19 What is 3 showing

Answer 21

Active transport of Na+

Question 22

q19 What is 2 showing

Answer 22

Active transport of K+

Question 23

q19 What is 1 showing

Answer 23

diffusion of Na+

Question 24

A molecule can enter the cell by two different passive processes. Which process would increase the rate at which this molecule enters the cells?

Answer 24

facilitated diffusion

Question 25

q17 the graph shows how the rate of entry of glucose into a cell changes as the concentration of glucose outside the cell changes. What causes the plateau at x?

Answer 25

All the carrier proteins are saturated with glucose

Question 26

Which ways of moving substances across cell surface membranes allows movement in both directions?

Answer 26

Active transport, diffusion, facilitated diffusion and osmosis

Question 27

When cylinders of potato tissue were immersed in 0.35 mol dm^-3 sucrose solution, they showed no change in mass. What happens when they’re immersed in 0.1 mol dm^-3 sucrose solution?

Answer 27

The water potential of the cells will become more negative