Mass Transport Flashcards
What is the function of the coronary arteries?
(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
The rise and fall in blood pressure in the aorta is greater than in the small
arteries.Suggest why.
(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
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.
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
Other than causing slow blood flow, explain one advantage of capillaries being
narrow.
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
What factor limits the minimum internal diameter of the lumen of a capillary?
Width / size / diameter of blood cell.
The volume of blood leaving the capillary network into the veins is less than the
volume of blood entering from the arteries.
(Fluid) in tissue fluid / (fluid) in lymph.
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.
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.
Apoplastic
- Non-living cells, through the cell walls
-Water can diffuse straight though to the next cell
Cell wall to cell wall by capillary action
Symplastic
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
Evidence supporting mass flow
- There is pressure within the sieve tubes, as shown by sap being released when they are cut.
- The conc of sucrose higher in source than in sink (roots)
- Downward flow in phloem happens in daylight, not when in shade or night
- Increase sucrose levels in leaf results to increase sucrose levels in phloem
- Metabolic poisons/lack of 02 inhibit translocation
- Campanion cells -many mitacondria -a lot of ATP.
Evidence against mass flow
- Function of seive plate unclear, may have a structural function help prevent burst
- Not all solute move at same speed
- Sucrose delivery same other than going quickly to lower conc of sucrose
ii) Once in the root hairs, water is drawn into the roots, down a water potential gradient. Explain how this process occurs. (3 marks)
– 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
iii) ‘Water molecules are cohesive’ what is meant by this term in relation to the movement of water in the xylem? (3 marks)
– water molecules stick together - transpirational pull forms a continuous column of water through the plant
- water column moves is pulled up towards the leaf
i) The loss of water from a plant occurs through gas exchange. Explain this process. (2 marks)
stomata opens so carbon dioxide can enter
-water is lost from the stomata because the water potential is higher inside the leaf than outside
Describe how the mass flow hypothesis for the mechanism of translocation in the plants.
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.
