Transport Across Cell Membranes- exam q Flashcards
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
