Transport Across Cell Membranes- exam q Flashcards
(16 cards)
Figure 1 shows a cell from the lining of the ileum specialised for absorption of
products of digestion.
SGLT1 is a carrier protein found in the cell-surface membrane of this cell, it
transports glucose and sodium ions (Na+
) into the cell.
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.
(ATP to ADP + Pi ) Releases energy;
- (energy) allows ions to be moved against a concentration gradient
OR
(energy) allows active transport of ions;
The movement of Na+ out of the cell allows the absorption of glucose into
the cell lining the ileum.
Explainnhow
(Maintains/generates) a concentration/diffusion gradient
for Na+ (from ileum into cell);
2. Na+ moving (in) by facilitated diffusion, brings glucose with it
OR
Na+ moving (in) by co-transport, brings glucose with it;
Describe and explain two features you would expect to find in a cell
specialised for absorption.
Folded membrane/microvilli so large surface area
2. Large number of co-transport/carrier/channel proteins so
fast rate (of absorption)
OR
Large number of co-transport/carrier proteins for active transport
OR
Large number of co-transport/carrier/channel proteins for facilitated
diffusion;
3. Large number of mitochondria so make (more) ATP (by respiration)
OR
Large number of mitochondria for aerobic respiration
OR
Large number of mitochondria to release energy for active transport;
4. Membrane-bound (digestive) enzymes so maintains
concentration gradient (for fast absorption);
The movement of substances across cell membranes is affected by
membrane structure. Describe how. (5)
- Phospholipid (bilayer) allows movement/diffusion of nonpolar/lipid-soluble substances;
- Phospholipid (bilayer) prevents movement/diffusion of polar/
charged/lipid-insoluble substances
OR
(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; - Cholesterol affects fluidity/rigidity/permeability;
The cells of beetroot contain a red pigment. A student investigated the effect of
temperature on the loss of red pigment from beetroot. He put discs cut from
beetroot into tubes containing water. He maintained each tube at a different
temperature. After 25 minutes, he measured the percentage of light passing
through the water in each tube.
(a) 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);
OR
(If) too little water the concentration of pigment (in solution) will
be greater / solution will appear darker / less light passes
through (than expected); - So results (from different temperatures) are comparable;
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 pigmen
- Damage to (cell surface) membrane;
- (membrane) proteins denature;
- Increased fluidity / damage to the phospholipid bilayer;
In mammals, in the early stages of pregnancy, a developing embryo exchanges
substances with its mother via cells in the lining of the uterus. At this stage, there
is a high concentration of glycogen in cells lining the uterus.
(c) Suggest and explain two ways the cell-surface membranes of the cells
lining the uterus may be adapted to allow rapid transport of nutrients.
- Membrane folded so increased / large surface area;
OR
Membrane has increased / large surface area for (fast)
diffusion / facilitated diffusion / active transport / co-transport; - Large number of protein channels / carriers (in membrane) for
facilitated diffusion; - Large number of protein carriers (in membrane) for active
transport; - Large number of protein (channels / carriers in membrane) for
co-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.
) 1. Co-transport;
2. Uses (hydrolysis of) ATP;
3. Sodium ion and proton bind to the protein;
4. Protein changes shape (to move sodium ion and / or proton
across the membrane);
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.
- (Higher salt) results in lower water potential of tissue fluid;
- (So) less water returns to capillary by osmosis (at venule end);
OR - (Higher salt) results in higher blood pressure / volume;
- (So) more fluid pushed / forced out (at arteriole end) of
capillary;
Compare and contrast the processes by which water and inorganic ions
enter cells
) 1. Comparison: both move down concentration gradient;
2. Comparison: both move through (protein) channels in membrane;
Accept aquaporins (for water) and ion channels
3. Contrast: ions can move against a concentration gradient by active
transport
Contrast the processes of facilitated diffusion and active transport
- Comparison: both move down concentration gradient;
- Comparison: both move through (protein) channels in membrane;
Accept aquaporins (for water) and ion channels - Contrast: ions can move against a concentration gradient by active
transport
Cholesterol increases the stability of plasma membranes. Cholesterol does this by making membranes less flexible.
(f) Suggest one advantage of the different percentage of cholesterol in red blood cells
compared with cells lining the ileum.
Red blood cells are free in blood
or not supported by other cells so cholesterol helps to maintain shape
(g) E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell
maintains a constant shape. Explain why.
Cell unable to change shape
Because cell has cell wall
Wall is made of peptidoglycan/murein
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 - Rate of uptake proportional to (external) concentration;
Between C and D
Accept description of proportional - All channel / carrier proteins in use / saturated / limiting;
Accept used up
Accept transport proteins
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.
- Method to ensure all cut surfaces of the eight cubes are exposed to
the sucrose solution;
Credit valid method descriptions to fulfil mp1, 2 and
3 (no explanation is required). - Method of controlling temperature;
Accept ‘at room temperature’ for method - Method of drying cubes before measuring;
- Measure mass of cubes at stated time intervals;
Accept time intervals between every 5 minutes with
maximum of every 40 minutes.
Accept ‘weigh the cubes at stated time intervals’
Scientists investigated the use of a drug called Tenapanor to reduce salt
absorption in the gut. Tenapanor inhibits the carrier protein, NHE3.
The scientists fed a diet containing a high concentration of salt to two
groups of rats, A and B.
* The rats in Group A were not given Tenapanor (0 mg kg−1).
* The rats in Group B were given 3 mg kg−1 Tenapanor.
One hour after treatment, the scientists removed the gut contents of the
rats and immediately weighed them.
Their results are shown in the table.
Concentration of Tenapanor / mg kg−1
0,
3
Mean mass of contents
of the gut / g
2.0
4.1
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; - There is a less than 0.05 probability that the difference is due to
chance; - (More salt in gut) reduces water potential in gut (contents);
- (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
