6. Continued Lipids, Cell Membranes & transport across cell membranes Flashcards
q21 Explain, with reference to Fig 2.2, whether the PAP extracted from M. charantia is a PAP1 or a PAP2 enzyme 2
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+
With reference to Fig 2.3, describe & explain the effect of increasing phosphatide concentration on PAP activity 3
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.
Explain why phospholipids are able to form a bilayer in cell membranes 2
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
q22 Name structure P
Channel protein
q22 Name structure Q
Glycoprotein
q22 Name structure R
Cholesterol
q22 Name structure W
Phospholipid bilayer
q22 State the function of channel proteins
To provide a channel across the membrane for polar ions & molecules to pass through
q22 State the function of glycoproteins
Allows cells to recognise each other & initiate immune responses
q22 State the function of cholesterol 3
Provides stability and maintains fluidity of the cell membrane
Prevents phospholipids being tightly packed
Serves as myelin sheath in nerve cells
q22 State the function of phospholipids 2
Main component of cell surface membrane
controls what enters and leaves the cell
Explain what is meant by fluid mosaic 3
Cell membrane is a collection of different structures that resembles a mosaic
proteins and phospholipids can move about by diffusion, causing fluidity
Describe how phospholipid molecules are arranged in a cell surface membrane 2
Non-polar, hydrophobic tails face inwards, creating a hydrophobic channel
while polar, hydrophilic heads face outwards
State 2 ways in which phospholipids differ from triglycerides 2
triglycerides have 3 fatty acid tails whole phospholipids have 2
phospholipid tails are different lengths while triglyceride tails are all the same length
Explain how the structure of triglycerides makes them more suitable for energy storage than carbohydrates 2
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
Name the type of membrane protein to which the cell signalling molecules bind
Cell surface receptors
q24 a) The Visking tubing used by the student wasn’t permeable to sucrose. Explain the results shown in table 3.1 3
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
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
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.
q20 in which direction will the water move?
From cell x to both cells Y and z
q19 What is 4 showing
diffusion of K+
q19 What is 3 showing
Active transport of Na+
q19 What is 2 showing
Active transport of K+
q19 What is 1 showing
diffusion of Na+
A molecule can enter the cell by two different passive processes. Which process would increase the rate at which this molecule enters the cells?
facilitated diffusion
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?
All the carrier proteins are saturated with glucose
Which ways of moving substances across cell surface membranes allows movement in both directions?
Active transport, diffusion, facilitated diffusion and osmosis
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?
The water potential of the cells will become more negative
