Cell Transport Exam Questions Flashcards
(21 cards)
The movement of substances across cell membranes is affected by membrane structure.
Describe how.
Phospholipid bilayer allows movement / diffusion
Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid
insoluble substances
(Membrane) proteins allow polar/charged substances to cross the
membrane/bilayer;
Carrier proteins allow active transport;
Channel/carrier proteins allow facilitated diffusion/co-transport;
Shape/charge of channel / carrier determines which substances move;
Number of channels/carriers determines how much movement;
Membrane surface area determines how much diffusion/movement;
Give one similarity and two differences between the membrane structure
shown in Figure 2 and the fluid-mosaic model of membrane structure.
similarity
both have a phospholipid bilayer
differences
fluid mosaic has carrier protein
cholesterol is not present but in fluid mosaic model it is
The action of the carrier protein X in Figure 1 is linked to a
membrane-bound ATP hydrolase enzyme.
Explain the function of this ATP hydrolase.
converts ATP into ADP + Pi to release energy
for active transport
Name and describe five ways substances can move across the
cell-surface membrane into a cell.
simple diffusion
movement of small molecules / NON-polar down a concentration gradient
active transport
movement of sugars e.g. amino acids from a low conc to a high conc using ATP and carrier proteins against a conc gradient
faciliated diffusion
movement of molecules down a concentration gradient via channel/carrier proteins
osmosis
movement of water down a water potential gradient
Co-transport
movement of 2 different substances using a carrier protein;
Describe and explain two features you would expect to find in a cell
specialised for absorption.
many carrier proteins to increase rate for active transport
many microvilli to increase surface area for absorption
folded membrane increasing surface area
Give two similarities in the movement of substances by diffusion and by
osmosis.
moves molecules against a conc gradient high to low
does not use energy from respiration / ATP
Use your knowledge of transport across membranes to explain the shape
of the curve in the graph for uptake of monosaccharides between
concentrations:
A and B
C and D
Movement through carrier proteins;
OR
Facilitated diffusion;
Between A and B
Accept channel proteins
Rate of uptake proportional to (external) concentration;
Between C and D
3. All channel / carrier proteins in use / saturated / limiting;
The graph is evidence for monoglycerides being lipid-soluble molecules.
Suggest how
- Rate of uptake is proportional / does not level off (so diffusion
occurring);
Accept as one increases the other increases - (Lipid-soluble molecules) diffuse through / are soluble in phospholipid
(bilayer);
Describe the method the student would have used to obtain the results in
the graph. Start after all of the cubes of potato have been cut. Also
consider variables he should have controlled.
control temperature
Measure mass of cubes at stated time intervals
dry cubes before measuring
Method to ensure all cut surfaces of the eight cubes are exposed to
the sucrose solution;
The student put the same volume of water in each tube.
Explain why it was important that he controlled this experimental variable
(If) too much water the concentration of pigment (in solution) will be
lower / solution will appear lighter / more light passes through (than
expected);
The decrease in the percentage of light passing through the water between
25 °C and 60 °C is caused by the release of the red pigment from cells of
the beetroot.
Suggest how the increase in temperature of the water caused the release
of the red pigment.
- Damage to (cell surface) membrane;
- (membrane) proteins denature;
- Increased fluidity / damage to the phospholipid bilayer;
Suggest and explain two ways the cell-surface membranes of the cells
lining the uterus may be adapted to allow rapid transport of nutrients.
folded membrane increases surface area
many carrier proteins to increase rate of active transport
Sodium ions from salt (sodium chloride) are absorbed by cells lining the
gut. Some of these cells have membranes with a carrier protein called
NHE3.
NHE3 actively transports one sodium ion into the cell in exchange for one
proton (hydrogen ion) out of the cell.
Use your knowledge of transport across cell membranes to suggest how
NHE3 does this.
- Co-transport;
- Uses (hydrolysis of) ATP;
- Sodium ion and proton bind to the protein;
- Protein changes shape (to move sodium ion and / or proton
across the membrane);
The scientists carried out a statistical test to see whether the difference in
the means was significant. They calculated a P value of less than 0.05.
They concluded that Tenapanor did reduce salt absorption in the gut.
Use all the information provided and your knowledge of water potential to
explain how they reached this conclusion.
. Tenapanor / (Group)B / drug causes a significant increase;
OR
There is a significant difference with Tenapanor / drug /
between A and B;
2. There is a less than 0.05 probability that the difference is due to
chance;
3. (More salt in gut) reduces water potential in gut (contents);
4. (so) less water absorbed out of gut (contents) by osmosis
OR
Less water absorbed into cells by osmosis
OR
Water moves into the gut (contents) by osmosis.
OR
(so) water moves out of cells by osmosis.
High absorption of salt from the diet can result in a higher than normal
concentration of salt in the blood plasma entering capillaries. This can lead
to a build-up of tissue fluid.
Explain how.
high salt conc causes lower water potential in tissue fluid
less water moves in by osmosis to return to capillary at venule end
Compare and contrast the processes by which water and inorganic ions
enter cells
- Comparison: both move down concentration gradient;
- Comparison: both move through (protein) channels in membrane;
- Contrast: ions can move against a concentration gradient by active
transport
Contrast the processes of facilitated diffusion and active transport.
active transport moves molecules from a low to high conc whereas faciliated moves from high to low
active transport uses ATP and carrier proteins whereas faciliated uses both carrier and channel proteins
Calculate the ratio of the mean rate of uptake of chloride ions in the first
hour to the rate of uptake of chloride ions in the second hour for group B
plants.
Explain the results shown in the figure above.
3.3:1
1. Group A – initial uptake slower because by diffusion (only);
2. Group A – levels off because same concentrations inside cells
and outside cells / reached equilibrium;
3. Group B – uptake faster because by diffusion plus active
transport;
4. Group B fails to level off because uptake against gradient / no
equilibrium to be reached;
5. Group B – rate slows because few / fewer chloride ions in
external solution / respiratory substrate used up.
suggest one advantage of the different percentage of cholesterol in red blood cells compared with the cells lining ileum
red blood cells are free in the blood so cholesterol can help maintain the shape
E. coli has no cholesterol in its cell surface membrane. despite this, the cell maintains a constant shape. Explain why
E coli has a cell wall contains murein
cell unable to change shape
Using your knowledge of cell surface membrane suggest how LDL enters the cell
LDL attaches to receptors then enters through carrier protein
