Topic 3 - Transport

Question 1

Surface area to volume ratio

Answer 1

As size increases, ratio (of surface area to volume) decreases;
Comparison required, e.g., smaller organisms have a larger ratio

Question 2

Insect – structural adaptations

Answer 2

1. Tracheoles have thin walls so short diffusion distance to cells;
2. Highly branched / large number of tracheoles so short diffusion distance to cells;
3. Highly branched / large number of tracheoles so large surface area (for gas exchange);
4. Tracheae provide tubes full of air so fast diffusion (into insect tissues);
5. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface;
   OR
   Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);
6. Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;

Question 3

Fish – structural adaptation

Answer 3

1. Many lamellae / filaments so large surface area;
2. Thin (surface) so short diffusion pathway;

Question 4

Fish - Countercurrent mechanism

Answer 4

1. Water and blood flow in opposite directions;
   Allow diagram showing counter-flow
2. Blood always passing water with a higher oxygen concentration;
3. Diffusion gradient maintained throughout length (of gill)
   OR
   Diffusion occurs throughout length of gill
   OR
   If water and blood flowed in same direction equilibrium would be reached

Question 5

Gas exchange system

Answer 5

1. Named structures – trachea, bronchi, bronchioles, alveoli;
2. Above structures named in correct order
3. Breathing in – diaphragm contracts and external intercostal muscles contract;
4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);
5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);
   For thoracic cavity accept ‘lungs’ or ‘thorax’.

Question 6

Inhalation mechanism

Answer 6

1. Diaphragm (muscle) contracts and external intercostal muscles contract;
2. (Causes volume increase and) pressure decrease;
3. Air moves down a pressure gradient
   OR
   Air enters from higher atmospheric pressure

Question 7

Lung gas exchange adaptation

Answer 7

1. (The alveolar epithelium) is one cell thick;
   Reject thin membrane
2. Creating a short diffusion pathway / reduces the diffusion distance;

Question 8

Leaf adaptations for gas exchange

Answer 8

1. (Carbon dioxide enters) via stomata; Reject stroma
2. (Stomata opened by) guard cells;
3. Diffuses through air spaces;
4. Down diffusion gradient;

Question 9

Haemoglobin structure and binding

Answer 9

1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin;
2. Creates / leads to / uncovers second / another binding site
   OR
   Uncovers another iron / Fe / haem group to bind to;

Question 10

Bohr shift

Answer 10

1.   Increases/more oxygen dissociation/unloading
OR
Deceases haemoglobin’s affinity for O2;
2.   (By) decreasing (blood) pH/increasing acidity;

Question 11

Oxygen dissociation (shift to left)

Answer 11

1. lower affinity for O2 at low partial pressures;
   OR
   lower affinity for oxygen at pp found in tissues;
2. Easier unloading of O2 ;
3. For aerobic respiration at the tissues/muscles/cells
   OR
   Anaerobic respiration delayed at the tissues/muscles/cells
   OR
   Less lactate at the tissues/muscles/cells;

Question 12

Oxygen dissociation – high metabolism organism

Answer 12

1. Curve to the right so lower affinity / % saturation (of haemoglobin);
2. Haemoglobin unloads / dissociates more readily;
3. More oxygen to cells / tissues / muscles;
4. For greater / more / faster respiration;
   Idea of a higher rate of respiration

Question 13

What is digestion?

Answer 13

1. Hydrolysis (of);
2. (Large / insoluble substances) to small(er) / soluble substances;

Question 14

Starch digestion

Answer 14

1. Maltose;
2. Salivary amylase breaks down starch

Question 15

Protein digestion

Answer 15

1.   (Reference to) hydrolysis of peptide bonds;
2.   Endopeptidase act in the middle of protein/polypeptide
OR
Endopeptidase produces short(er) polypeptides/ increase number of ends;
3.   Exopeptidases act at end of protein/polypeptide
OR
Exopeptidase produces dipeptides/amino acids;
4.   Dipeptidase acts on dipeptide/between two amino acids
OR
Dipeptidase produces (single) amino acids

Question 16

Lipid digestion – bile salts

Answer 16

1. Small droplets have a larger surface area to volume ratio;
2. More surface for lipase (to act), leading to faster digestion of triglycerides;

Question 17

Lipid absorption

Answer 17

1. Micelles contain bile salts and fatty acids/monoglycerides;
2. Make fatty acids/monoglycerides (more) soluble (in water) OR Bring/release/carry fatty acids/monoglycerides to cell/lining (of the iluem) OR Maintain high(er) concentration of fatty acids/monoglycerides to cell/lining (of the ileum);
3. Fatty acids/monoglycerides absorbed by diffusion;
4. Triglycerides (re)formed (in cells);
5. Vesicles move to cell membrane;

Question 18

Golgi and lipid absorption

Answer 18

1. Modifies / processes triglycerides;
2. Combines triglycerides with proteins;
3. Packaged for release / exocytosis
   OR
   Forms vesicles;

Question 19

Ventricular systole

Answer 19

1. Atrium has higher pressure than ventricle (due to filling / contraction) causing atrioventricular valves to open;
2. Ventricle has higher pressure than atrium (due to filling / contraction) causing atrioventricular valves to close;
3. Ventricle has higher pressure than aorta causing semilunar valve to open;
   Points 1, 2 and 3 must be comparative: eg higher
4. Higher pressure in aorta than ventricle (as heart relaxes) causing semilunar valve to close;
5. (Muscle / atrial / ventricular) contraction causes increase in pressure

Question 20

Name the blood vessel that carries the blood to:
The heart
The kidneys
The lungs

Answer 20

Coronary arteries
Renal artery
Pulmonary artery

Question 21

Artery and arteriole structure

Answer 21

Elastic tissue
1. Elastic tissue stretches under pressure / when heart beats then recoils / springs back;
2. Evens out pressure / flow;
Muscle
3. Muscle contracts to reduce diameter of lumen / vasoconstriction / constricts vessel;
4. Changes flow / pressure;
Epithelium
5. Epithelium smooth;
6. Reduces friction / blood clots / less resistance

Question 22

Aorta structure to function

Answer 22

1. Elastic tissue to allow stretching / recoil / smoothes out flow of blood / maintains pressure;
2. (Elastic tissue) stretches when ventricles contract
   OR Recoils when ventricle relaxes;
3. Muscle for contraction / vasoconstriction;
4. Thick wall withstands pressure OR stop bursting;
5. Smooth endothelium reduces friction;
6. Aortic valve / semi-lunar valve prevents backflow

Question 23

Explain how the atrioventricular valve maintains a unidirectional flow of blood

Answer 23

1.   Pressure in (left) atrium is higher than in ventricle/B causing valve to open;
OR
(When) pressure above valve is higher than below valve it opens;
2.   Pressure in (left) ventricle/B is higher than in atrium causing valve to close;
OR
(When) pressure in below valve is higher than above valve it closes;

Question 24

Tissue fluid formation and high blood pressure

Answer 24

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.
   Allow lymph system not able to drain tissues fast enough

Question 25

Dissection safety

Answer 25

Use a sharp scalpel/scissors
Wash hands/wear gloves
Disinfect bench/equipment
Cover any cuts
Cut away from self/others/on a hard surface
Safe disposal

Question 26

Transpiration

Answer 26

1. Stomata open and photosynthesis increases / transpiration increases;
2. More water pulled up due to cohesion between water molecules / by cohesion tension;
3. Water pulled up trunk / moves up at fast rate under tension;
4. Sticking / adhesion (between water and) cells / walls / pulls xylem in;

Question 27

Factors affecting rate of transpiration

Answer 27

Light;
Humidity / moisture in air;
Air movement / wind;
Temperature;

Question 28

Xerophyte adaptations

Answer 28

1. Hairs so ‘trap’ water vapour and water potential gradient decreased;
2. Stomata in pits/grooves so ‘trap’ water vapour and water potential gradient decreased;
3. Thick (cuticle/waxy) layer so increases diffusion distance;
4. Waxy layer/cuticle so reduces evaporation/transpiration.
5. Rolled/folded/curled leaves so ‘trap’ water vapour and water potential gradient decreased;
6. Spines/needles so reduces surface area to volume ratio

Question 29

Translocation

Answer 29

1. (At source) sucrose is actively (transported) into the phloem/sieve element/tube;
2. By companion/transfer cells;
3. Lowers water potential in phloem/sieve element/tube and water enters by osmosis;
4. (Produces) high (hydrostatic) pressure;
5. Mass flow/transport towards sink/roots/storage tissue;
6. At sink/roots sugars are removed/unloaded;

Question 30

Evidence for mass flow

Answer 30

In support of mass flow hypothesis
1. phloem is involved;
2. respiration / active transport is involved (in flow / movement);
3. Because 4 °C / cooling reduces / slows / stops flow / movement;
4. The agar block is the source;
5. Roots are the sink;
Against the mass flow hypothesis
6. No bulge above ringing ;
7. No (role for) osmosis / hydrostatic pressure / water movement;
8. Movement could be due to gravity;
9. Roots still grow without (intact/functioning) phloem;
10. No leaves / sugars / photosynthesis to act as a source;