PMT Transport across cell membranes question

Question 1

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

Answer 1

1. (Simple) diffusion of small/non-polar molecules down a concentration gradient;
2. Facilitated diffusion down a concentration gradient via
   carrier protein or channel protein
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 2

Explain the function of this ATP hydrolase when linked to the carrier protein that actively transports Na+ ions out

Answer 2

ATP is hydrolysed ADP + Pi which Releases energy;
2. (energy) allows ions to be moved against a concentration gradient
(energy) allows active transport of ions;

Question 3

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

Answer 3

movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum because

It Maintains a concentration/diffusion gradient for Na+ from ileum into cell
Maintains concentration gradient
of Na+ inside the cell compared with outside the
cell’.
Na+ moving (in) by facilitated diffusion, brings glucose with it
Na+ moving (in) by co-transport, brings glucose with it;

Question 4

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

Answer 4

Features found in cell specialised for absorption are
1. Folded membrane and microvilli so large surface area for absorption

2. Large number of co-transporters or carrier and channel proteins so
   fast rate of absorption

Large number of co-transport and carrier proteins for active transport
or
Large number of co-transport
and carrier and channel proteins for facilitated
diffusion;

3. Large number of mitochondria to make more ATP by aerobic respiration and for aerobic respiration

Large number of mitochondria to release energy for active transport;

4. Membrane-bound digestive enzymes to maintain concentration gradient for fast absorption

Question 5

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

Answer 5

The movement of substances across cell membranes is affected by
membrane structure because

1. Phospholipid bilayer allows movement and diffusion of nonpolar and lipid-soluble substances;
2. Phospholipid (bilayer) prevents movement and diffusion of polar and
   charged and lipid-insoluble substances
3. Carrier proteins allow active transport;
4. Channel and carrier proteins allow facilitated diffusion and co-transport;
5. Shape and 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 and permeability;

Question 6

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

Answer 6

(Movement) is down a gradient / from high concentration to low
concentration; for both

2.Both are Passive / not active processes;

BothDo not use energy from respiration and hydrolysis of ATP

Both Use inbuild kinetic energy from the molecule/ solution;

Question 7

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 7

Membrane folded so increased / large surface area;

Membrane has increased / large surface area for (fast)
diffusion / facilitated diffusion / active transport / co-transport;
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 8

Compare and contrast the processes by which water and inorganic ions
enter cells.

Answer 8

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

Question 9

(a) Contrast the processes of facilitated diffusion and active transport.

Answer 9

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.