mass transport

Question 1

Describe the mass flow hypothesis for the mechanism of translocation in plants.

Answer 1

1. In source / leaf sugars actively transported into phloem;
2. By companion cells;
3. Lowers water potential of sieve cell / tube and water enters by osmosis;
4. Increase in pressure causes mass movement (towards sink / root);
5. Sugars used / converted in root for respiration for storage.

Question 2

One theory of translocation states that organic substances are pushed from a high
pressure in the leaves to a lower pressure in the roots.
Describe how a high pressure is produced in the leaves.

Answer 2

Water potential becomes lower / becomes more negative (as sugar enters
phloem)

2. Water enters phloem by osmosis;
3. Increased volume (of water) causes increased pressure

Question 3

Using the diagram, suggest and explain one other way in which companion
cells are adapted for the transport of sugars between cells.

Answer 3

1. Mitochondria release energy / ATP / site of respiration;
   Q Reject: ‘produce energy’
   but accept produce energy in form of ATP
2. For active transport / uptake against concentration gradient.

Question 4

Using the diagram, suggest and explain one other way in which sieve cells are
adapted for mass transport.

Answer 4

1. No / few organelles / very little cytoplasm / cytoplasm at
   edge / more room / hollow / large vacuole / large space /
   thick walls;
   Accept strong walls for thick walls
2. (So) easier / more flow / (thick / strong walls) resist pressure.
   Easier flow may be expressed in other ways e.g. lower
   resistance to flow

Question 5

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

Answer 5

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 6

why is the water potential lower at the venule end of the capillary

Answer 6

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 7

Describe how proteins are digested in the human gut

Answer 7

1. Hydrolysis of peptide bonds;
2. Endopeptidases break polypeptides into smaller peptide chains;
3. Exopeptidases remove terminal amino acids;
4. Dipeptidases hydrolyse / break down dipeptides into amino acids.

Question 8

how are carbohydrates digested

Answer 8

1. saliva enters the mouth via salivary glands
2. saliva contains salivary amylase which hydrolysis starch in the food to maltose
3. food enters the stomach which is acidic. The acid denatures amylase and prevents further breakdown of starch
4. food passes into the small intestine where it mixes with the pancreatic juices
5. the juices contain pancreatic amylase which continues to hydrolysed any starch into maltose
6. muscles in the intestine walls push the food along to the ileum
7. the epithelium lining has membrane-bound disaccharides. This hydrolysis the maltose into alpha glucose