Mass Transport

Question 1

What is the function of the coronary arteries?

Answer 1

(Carry) oxygen / glucose;
Accept: oxygenated blood
Ignore references to removing waste products
Ignore references to arteries ‘pumping’ blood
2. (To) heart muscle / tissue / cells / myocytes.
Must be supply to heart or cardiac

Question 2

The rise and fall in blood pressure in the aorta is greater than in the small
arteries.Suggest why.

Answer 2

(Aorta)
1. (is) close / directly linked to the heart / ventricle / pressure is higher / is
very high;
2. (Aorta has) elastic tissue;
Accept elasticity
Ignore reference to muscle
3. (Aorta has) stretch / recoil.
Q Reject: contracts / relaxes / pumps
Accept: for mp 2 and mp 3, converse for small arteries if
qualified by little / less

Question 3

Although the speed of blood flow in an arteriole is greater than speed of blood flow
in a capillary, blood does not accumulate in the arterioles.

Answer 3

a) 1. Many / more capillaries (than arterioles);
2. (Cross-sectional) area of capillaries (much) greater (than of arterioles).
Note: maximum of 1 mark for this question

Question 4

Other than causing slow blood flow, explain one advantage of capillaries being
narrow.

Answer 4

Short pathway / short distance between blood and outside of capillary;
Reference to blood and cells required
2. Large surface area (of blood) in contact with walls of capillaries;
Idea is per unit volume of blood but candidates need not say
this
3. Fast exchange / fast diffusion / fast osmosis.
Must relate to increased speed

Question 5

What factor limits the minimum internal diameter of the lumen of a capillary?

Answer 5

Width / size / diameter of blood cell.

Question 6

The volume of blood leaving the capillary network into the veins is less than the
volume of blood entering from the arteries.

Answer 6

(Fluid) in tissue fluid / (fluid) in lymph.

Question 7

4.A principle of homeostasis is the maintenance of a constant internal environment. An
increase in the concentration of carbon dioxide would change the internal environment
and blood pH.
Explain the importance of maintaining a constant blood pH.

Answer 7

M4.(Maintaining constant pH to avoid)
1. Named protein / enzyme (in blood) sensitive to / affected by change in
pH;
Accept converse for MP2 and MP3.
Named example should be a protein that might be affected
(by change in pH) eg haemoglobin, carrier protein in plasma
membrane.
Accept ‘change in H+
concentration’ for ‘change in pH’.
2. (Resultant) change of charge / shape / tertiary structure;
The change in charge idea relates to the enzyme / protein
and not the blood (plasma) or red blood cells.
‘Denaturation’ alone is insufficient.
3. Described effect on named protein or enzyme.
e.g. less oxygen binds with haemoglobin / less transport across membranes /
fewer substrates can fit active site / fewer enzyme-substrate complexes.

Question 8

Apoplastic

Answer 8

• Non-living cells, through the cell walls
  -Water can diffuse straight though to the next cell
  Cell wall to cell wall by capillary action

Question 9

Symplastic

Answer 9

cell to cell by osmosis

• the endodermas actively transports potassium ions into the xylem causing the water to move by osmosis.
• water moves through living parts of the cell
• Through the cytoplasm
• Passes through plasmodesmata between cells

Question 10

Evidence supporting mass flow

Answer 10

1. There is pressure within the sieve tubes, as shown by sap being released when they are cut.
2. The conc of sucrose higher in source than in sink (roots)
3. Downward flow in phloem happens in daylight, not when in shade or night
4. Increase sucrose levels in leaf results to increase sucrose levels in phloem
5. Metabolic poisons/lack of 02 inhibit translocation
6. Campanion cells -many mitacondria -a lot of ATP.

Question 11

Evidence against mass flow

Answer 11

1. Function of seive plate unclear, may have a structural function help prevent burst
2. Not all solute move at same speed
3. Sucrose delivery same other than going quickly to lower conc of sucrose

Question 12

ii) Once in the root hairs, water is drawn into the roots, down a water potential gradient. Explain how this process occurs. (3 marks)

Answer 12

– Water moves from an area of high water potential to an area of low water potential
-High water potential in the soil -Low water potential in the leaves - Permanent gradient

Question 13

iii) ‘Water molecules are cohesive’ what is meant by this term in relation to the movement of water in the xylem? (3 marks)

Answer 13

– water molecules stick together - transpirational pull forms a continuous column of water through the plant
- water column moves is pulled up towards the leaf

Question 14

i) The loss of water from a plant occurs through gas exchange. Explain this process. (2 marks)

Answer 14

stomata opens so carbon dioxide can enter

-water is lost from the stomata because the water potential is higher inside the leaf than outside

Question 15

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

Answer 15

In the source, sugars actively transported into phloem by companion cells. This lowers water potential of sieve cells and so water enters phloem by osmosis from the xylem. This increases the hydrostatic pressure which causes mass movement towards sink. Sugars are used in the roots for respiration or are converted into starch for storage. Mass movement from source to sink.

Question 16

Explain Mass Flow hypothesis?

Answer 16

Active transport is used to actively load the sucrose from photosynthesis from companion cells into the sieve tubes of the phloem at the leaves. This lowers the water potential in the sieve tube so water enters the tubes by osmosis from the xylem and companion cells. This creates a high pressure inside the sieve tubes at the source end of the phloem. At the sink end solutes are removed from the phloem used up. This increases the water potential inside the sieve tubes so water also leaves the tubes by osmosis.This lowers the pressure inside the sieve tube at the sink end of the phloem.This results in a pressure gradient from the source end to the sink end. And this gradient pushed solutes along the sieve tubes towards the sink where they will be used in respiration or stored

Question 17

Xylem transports water through a plant. Describe and explain how the cells of xylem
are adapted for this function.

Answer 17

Thick cell walls withstand tension.Lignin in cell walls.Walls waterproof. Xylem cells have no end walls so this allows for a continuous column of water. Xylem vessels are stacked on top of each other so a continuous column of water. Have no cytoplasm so reduces resistance to flow of water. Xylem cells have pores in side walls which enables sideways flow.Narrow tubes increased surface area for adhesion. Molecules in cell walls allows adhesion.

Question 18

What is atheroma and how may it cause myocardial infarction? (5)

Answer 18

1. Cholesterol/ plaque / lipoprotein / LDL / fatty material / cells;
2. In artery wall / under lining / endothelium of artery / blood vessel;
3. Atheroma linked with blood clotting / thrombosis;
4. (Blocks) coronary artery / artery supporting heart muscle / tissue / cells;
5. Reduces oxygen / glucose supply (to heart muscle / tissues / cells);
6. (Heart muscle / tissue / cells) unable to respire / dies;

Question 19

Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta. (5)

Answer 19

1. Atrium has higher pressure than ventricle (due to filling/contraction);
2. Atrioventricular valve opens;
3. Ventricle has higher pressure than atrium (due to filling/contraction);
4. Atrioventricular valve closes;
5. Ventricle has higher pressure than aorta;
6. Semilunar valve opens;
7. Higher pressure in aorta than ventricle (as heart relaxes);
8. Semilunar valve closes;
9. (Muscle/atrial/ventricular) contraction causes increase in pressure;