plasma membrane questions

Question 1

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

Answer 1

Both have a phospholipid bilayer

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

Question 2

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

Answer 2

1. (Simple) diffusion of small 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 3

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 3

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

Folded membrane/ microvilli so large surface area (for absorption);
2. Large number of co-transport/carrier/channel proteins so fast rate (of absorption)
3. Large number of mitochondria so make (more) ATP (by respiration)
4. Membrane-bound enzymes so maintains
concentration gradient

Question 6

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

Answer 6

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

Question 7

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

Answer 7

1. (Movement) down a gradient
2. Passive / not active processes;

Question 8

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 8

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 9

The cells of beetroot contain red pigment. student investigated the effect of temp on the loss of pigment. He put discs cut of beetroot into tubes containing water. He maintained each tube at a different temp. After 25 min, he measured the % of light passing through the water in each tube.
(a) student put equal vol of water in each tube. Explain he controlled this experimental variable.

Answer 9

1. (If) too much water the concentration of pigment will be lower / solution will appear lighter
2. So results (from different temperatures) are comparable

Question 10

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

Answer 10

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

Question 11

In mammals, early stages of pregnancy, an embryo exchanges
substances with its mother via cells in the lining of the uterus. this stage, has a high conc. of glycogen in cells lining the uterus.
(c) explain 2 ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients.

Answer 11

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

Question 12

Sodium ions from sodium chloride are absorbed by cells lining the gut. Some 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. how does NHE3 do this.

Answer 12

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 13

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.

Answer 13

1. (Higher salt) results in lower water potential of tissue fluid;
2. (So) less water returns to capillary by osmosis
3. (Higher salt) results in higher blood pressure / volume;
4. (So) more fluid pushed / forced out (at arteriole end) of capillary;

Question 14

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 14

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 15

Contrast the processes of facilitated diffusion and active transport.

Answer 15

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