Cells - Transport across Cell Membrane

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
   protein carrier/channel;
3. Osmosis of water down a water potential gradient;
   4.** Active transport **against a concentration gradient via
   protein carrier using ATP;
4. Co-transport of 2 different substances using a carrier protein;

Question 2

Explain the function of this ATP hydrolase.

Answer 2

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

1. (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;

Question 4

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

Answer 4

1. 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 (digestive) enzymes so maintains
   concentration gradient (for fast absorption);

Question 5

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

Answer 5

1. Phospholipid (bilayer) allows movement/diffusion of nonpolar/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. Membrane surface area determines how much
   diffusion/movement;
7. Cholesterol affects fluidity/rigidity/permeability;