Transport Across Cell Memvrane - Mark Scheme Answers (study Mind)

Question 1

.(a) Describe how you would test a piece of food for the presence of lipid.

Answer 1

1. Dissolve in alcohol, then add water;
2. White emulsion shows presence of lipid.

Question 2

Use the information in the figure above to explain how tissue fluid is formed.

Answer 2

1. (Overall) outward pressure of 3.2 kPa;
   2.Forces small molecules out of capillary.

Question 3

The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why.

Answer 3

Loss of water / loss of fluid / friction (against capillary lining).

Question 4

High blood pressure leads to an accumulation of tissue fluid. Explain how.

Answer 4

1. High blood pressure = high hydrostatic pressure;
2. Increases outward pressure from (arterial) end of capillary / reduces
   inward pressure at (venule) end of capillary;
3. (So) more tissue fluid formed / less tissue fluid is reabsorbed.

Question 5

The water potential of the blood plasma is more negative at the venule end of the
capillary than at the arteriole end of the capillary. Explain why.

Answer 5

1. Water has left the capillary;
2. Proteins (in blood) too large to leave capillary;
3. Increasing / giving higher concentration of blood proteins (and thus wp).

Question 6

The stomata close when the light is turned off.
Explain the advantage of this to the plant.

Answer 6

1. (Because) water is lost through stomata;
2. (Closure) prevents / reduces water loss;
3. Maintain water content of cells.

Question 7

The scientists gave an injection to a mouse to make it produce the monoclonal
antibody used in this investigation (line 7).
What should this injection have contained?

Answer 7

Regulator protein.

Question 8

LDL enters the liver cells (lines 3−4).
Using your knowledge of the structure of the cell-surface membrane, suggest how
LDL enters the cell.

Answer 8

1. Lipid soluble / hydrophobic
2. Enters through (phospholipid) bilayer

Goes through carrier / channel protein.

Question 9

Explain how the monoclonal antibody would prevent the regulator protein from
working (lines 7−8).

Answer 9

1. (Monoclonal antibody) has a specific tertiary structure / variable region /
   is complementary to regulator protein
2. Binds to / forms complex with (regulator protein)
3. (So regulator protein) would not fit / bind to the receptor / is not
   complementary to receptor

Question 10

Give two ways in which pathogens can cause disease.

Answer 10

1. (Releases) toxins;
2. Kills cells / tissues.

Question 11

Putting bee honey on a cut kills bacteria. Honey contains a high concentration of
sugar.
Use your knowledge of water potential to suggest how putting honey on a cut kills
bacteria.

Answer 11

1. Water potential in (bacterial) cells higher (than in honey) / water potential in honey lower (than in bacterial cells);
2. Water leaves bacteria / cells by osmosis;
3. (Loss of water) stops (metabolic) reactions.

Question 12

Give one similarity and two differences between the membrane structure
shown in Figure 2 and the fluid-mosaic model of membrane structure.

Answer 12

(Similarity)
1. Both have a phospholipid bilayer
Both have fatty acid/hydrophobic tails pointing in/. face each other

(Differences)
2. No channel/carrier proteins, whereas fluid mosaic does
3. Cholesterol is not present whereas it is present in fluid mosaic;

Question 13

Name and describe five ways substances can move across the
cell-surface membrane into a cell.

Answer 13

1. (Simple) diffusion of small/non-polar molecules down a concentration gradient;
2. Facilitated diffusion down a concentration gradient via protein carrier/channel;
3. Osmosis of water down a water potential gradient;
4. Active transport against a concentration gradient via protein carrier using ATP;
5. Co-transport of 2 different substances using a carrier protein;

Question 14

(a) 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.

Answer 14

1. (ATP to ADP + Pi ) Releases energy;
2. (energy) allows ions to be moved against a concentration gradient

Question 15

The movement of Na+ out of the cell allows the absorption of glucose into
the cell lining the ileum. - explain how

Answer 15

1. (Maintains/generates) a concentration/diffusion gradient for Na+ (from ileum into cell);
2. Na+ moving (in) by facilitated diffusion, brings glucose with it

Question 16

Describe and explain two features you would expect to find in a cell specialised for absorption.

Answer 16

1. Folded membrane/microvilli so large surface area (for absorption);
2. Large number of co-transport/carrier/channel proteins so fast rate (of absorption)

Large number of mitochondria so make (more) ATP (by respiration)

Question 17

The movement of substances across cell membranes is affected by membrane structure. Describe how.

Answer 17

1. Phospholipid (bilayer) allows movement/diffusion of non- polar/lipid-soluble substances;
2. Phospholipid (bilayer) prevents movement/diffusion of polar/
   charged/lipid-insoluble substances
3. Carrier proteins allow active transport;
4. Channel/carrier proteins allow facilitated diffusion/co-transport;
5. Shape/charge of channel / carrier determines which substances move;
6. Number of channels/carriers determines how much movement;
7. Membrane surface area determines how much
   diffusion/movement;
8. Cholesterol affects fluidity/rigidity/permeability;

Question 18

(a) Give two similarities in the movement of substances by diffusion and by
osmosis.

Answer 18

1. (Movement) down a gradient / from high concentration to low concentration;
2. Passive / not active processes;

Question 19

(b) 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

Answer 19

1. Movement through carrier proteins;

Between A and B
2. Rate of uptake proportional to (external) concentration;
Between C and D

3. All channel / carrier proteins in use / saturated / limiting;

Question 20

(c) The graph is evidence for monoglycerides being lipid-soluble molecules.
Suggest how.

Answer 20

1. Rate of uptake is proportional / does not level off (so diffusion occurring);
2. (Lipid-soluble molecules) diffuse through / are soluble in phospholipid (bilayer);

Question 21

(a) 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.

Answer 21

1. Method to ensure all cut surfaces of the eight cubes are exposed to the sucrose solution;
2. Method of controlling temperature;
3. Method of drying cubes before measuring;
4. Measure mass of cubes at stated time intervals;

Question 22

Q7.
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.

Answer 22

1. (If) too much water the concentration of pigment (in solution) will be
   lower / solution will appear lighter / more light passes through (than
   expected);
2. So results (from different temperatures) are comparable;

Question 23

Describe a method the student could have used to monitor the temperature
of the water in each tube.

Answer 23

(Take) readings (during the experiment) using a (digital) thermometer/ temperature sensor;

Question 24

(d) 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.

Answer 24

1. Damage to (cell surface) membrane;
2. (membrane) proteins denature;
3. Increased fluidity / damage to the phospholipid bilayer;

Question 25

(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.

Answer 25

1. Membrane folded so increased / large surface area; 2. Large number of protein channels / carriers (in membrane) for facilitated diffusion; 3. Large number of protein carriers (in membrane) for active transport; 4. Large number of protein (channels / carriers in membrane) for co-transport;

Question 26

(a) 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.

Answer 26

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);

Question 27

Water and inorganic ions have important biological functions within cells. (c) Compare and contrast the processes by which water and inorganic ions enter cells.

Answer 27

1. Comparison: both move down concentration gradient; 2. Comparison: both move through (protein) channels in membrane; 3. Contrast: ions can move against a concentration gradient by active transport

Question 28

Contrast the processes of facilitated diffusion and active transport.

Answer 28

1. Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins; 2. Facilitated diffusion does not use ATP / is passive whereas active transport uses ATP; 3. Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient.