TOPIC 3 exam questions

Question 1

Describe and explain the mechanism that causes lungs to fill with air

Answer 1

1. Diaphragm (muscle) contracts and external intercostal muscles
   contract;

Ignore ribs move up and out

2. (Causes volume increase and) pressure decrease;
3. Air moves down a pressure gradient
   Ignore along
   OR
   Air enters from higher atmospheric pressure;

Question 2

Describe and explain the advantage of the counter-current principle in gas
exchange across a fish gill.

Answer 2

1. Water and blood flow in opposite directions;
2. Maintains diffusion/concentration gradient of oxygen

Accept: converse for carbon dioxide

Accept: equilibrium not reached

OR

Oxygen concentration always higher (in water);

3. (Diffusion) along length of
   lamellae/filament/gill/capillary;
   Accept: all/whole of lamellae/filament//gill/capillary

Question 3

Use your knowledge of gas exchange in leaves to explain why plants
grown in soil with very little water grow only slowly.

Answer 3

1.Stomata close;

2. Less carbon dioxide (uptake) for less photosynthesis/glucose
   production;

Question 4

Describe the gross structure of the human gas exchange system and how
we breathe in and out.

Answer 4

1. Named structures – trachea, bronchi, bronchioles, alveoli;

Reject mp1 if structures from other physiological
systems are named but award mp2 if the correct
structures are in the correct order.

2. Above structures named in correct order
   OR

Above structures labelled in correct positions on a diagram;

Reject mp1 if structures from other physiological
systems are named but award mp2 if the correct
structures are in the 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);
   For thoracic cavity accept ‘lungs’ or ‘thorax’.
   Reference to ‘thoracic cavity’ only required once.
5. Breathing out - Diaphragm relaxes and internal intercostal muscles
   contract;
   Accept diaphragm relaxes and (external) intercostal
   muscles relax and lung tissue elastic (so recoils).
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’.

Reference to ‘thoracic cavity’ only required once.
If idea of thoracic cavity is missing or incorrect,
allow ECF for mark point 6.

Question 5

Explain three ways in which an insect’s tracheal system is adapted for
efficient gas exchange.

Answer 5

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 6

Explain two ways in which the structure of fish gills is adapted for efficient
gas exchange.

Answer 6

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

1 & 2 must each have a feature and a consequence

Question 7

Explain how the counter current mechanism in fish gills ensures the
maximum amount of the oxygen passes into the blood flowing through the
gills.

Answer 7

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 8

Describe the processes involved in the absorption and transport of
digested lipid molecules from the ileum into lymph vessels. (5)

Answer 8

1. Micelles contain bile salts and fatty acids/monoglycerides;

Ignore other correct components of micelles

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);

Accept lipid/fat for fatty acid/ monoglyceride

3. Fatty acids/monoglycerides absorbed by diffusion;
   Reject if absorbed by facilitated diffusion
   Ignore if micelles themselves are being absorbed
4. Triglycerides (re)formed (in cells);
   Accept chylomicrons form
5. Vesicles move to cell membrane;
   Accept exocytosis for ‘vesicles move’

Question 9

Explain the function of this ATP hydrolase.

Answer 9

1. (ATP to ADP + Pi ) Releases energy;
   Reject ‘produces/makes/creates energy’.
2. (energy) allows ions to be moved against a concentration gradient

Question 10

The movement of Na+ out of the cell allows the absorption of glucose into
the cell lining the ileum.

Answer 10

1. (Maintains/generates) a concentration/diffusion gradient
   for Na+ (from ileum into cell);
   Accept ‘(Maintains/generates) a lower concentration
   of Na+ inside the cell compared with outside the
   cell’.
2. Na+ moving (in) by facilitated diffusion, brings glucose with it
   OR
   Na+ moving (in) by co-transport, brings glucose with it;
   Accept ‘co-transporter’ for ‘co-transport’.

Question 11

Describe the role of micelles in the absorption of fats into the cells lining
the ileum. (5)

Answer 11

1. Micelles include bile salts and fatty acids;
   Ignore other correct components of micelles.
2. Make the fatty acids (more) soluble in water;
   For ‘fatty acids’ accept fats / lipids.
3. Bring/release/carry fatty acids to cell/lining (of the ileum);
   For ‘fatty acids’ accept fats/lipids.
4. Maintain high(er) concentration of fatty acids to cell/lining (of the
   ileum);
5. Fatty acids (absorbed) by diffusion;
   Reject if absorbed by facilitated diffusion
   Ignore if micelles themselves are being absorbed.
   Ignore references to monoglycerides.

Question 12

(a) Describe the role of enzymes in the digestion of proteins in a mammal.

Answer 12

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;
Accept chain/chain of amino acids/peptide for polypeptide

Accept digest/breakdown/ break for ‘act’
Mark points 2, 3 and 4 reject answers where substrate or
product is incorrect eg ‘Endopeptidase produces
dipeptides’
Ignore references to source and location of enzymes

Question 13

Cells lining the ileum of mammals absorb the monosaccharide glucose by
co-transport with sodium ions. Explain how.

Answer 13

1. Sodium ions actively transported from ileum cell to blood;
2. Maintains / forms diffusion gradient for sodium to enter cells from gut
   (and with it, glucose);
3. Glucose enters by facilitated diffusion with sodium ions;

Question 14

Give the pathway a red blood cell takes when travelling in the human
circulatory system from a kidney to the lungs.
Do not include descriptions of pressure changes in the heart or the role of
heart valves in your answer.

Answer 14

1. Renal vein;
2. Vena cava to right atrium;
3. Right ventricle to pulmonary artery;

Question 15

Tissue fluid is formed from blood at the arteriole end of a capillary bed.
Explain how water from tissue fluid is returned to the circulatory system.

Answer 15

1. (Plasma) proteins remain;
   Accept albumin/globulins/fibrinogen for (plasma)
   protein
2. (Creates) water potential gradient

OR
Reduces water potential (of blood);

3. Water moves (to blood) by osmosis;
4. Returns (to blood) by lymphatic system;

Question 16

Explain how an arteriole can reduce the blood flow into capillaries.

Answer 16

1. Muscle contracts;
2. Constricts/narrows arteriole/lumen;

Question 17

Describe the advantage of the Bohr effect during intense exercise.

Answer 17

1. Increases dissociation of oxygen;
   Accept unloading/ release/reduced affinity for
   dissociation
2. 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 18

Describe and explain the effect of increasing carbon dioxide concentration
on the dissociation of oxyhaemoglobin.

Answer 18

1. Increases/more oxygen dissociation/unloading

OR

Deceases haemoglobin’s affinity for O2;
Accept more readily
Accept releases more O2

2. (By) decreasing (blood) pH/increasing acidity;
   Reject if reference made to active site

Question 19

Explain the role of the heart in the formation of tissue fluid.

Answer 19

1. Contraction of ventricle(s) produces high
   blood / hydrostatic pressure;
2. (This) forces water (and some dissolved
   substances) out (of blood capillaries);
3. Do not accept contraction / pumping of the
   heart
4. Reject blood / plasma / tissue fluid forced out

Question 20

Phloem pressure is reduced during the hottest part of the day. Use
information in the graph above along with your understanding of
transpiration and mass flow to explain why.

Answer 20

1. High (rate of) transpiration/evaporation;
2. Water lost through stomata
   OR
   (High) tension in xylem;
3. (Causes) less water movement from xylem to phloem
   OR

Insufficient water potential in phloem to draw water from xylem;

Question 21

Describe the cohesion-tension theory of water transport in the xylem.

Answer 21

1. Water lost from leaf because of transpiration / evaporation of water
   (molecules) / diffusion from mesophyll / leaf cells;

OR

Transpiration / evaporation / diffusion of water (molecules)
through stomata / from leaves;

2. Lowers water potential of mesophyll / leaf cells;
3. Water pulled up xylem (creating tension);
4. Water molecules cohere / ‘stick’ together by hydrogen bonds;
5. (forming continuous) water column;
6. Adhesion of water (molecules) to walls of xylem;

Question 22

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

Answer 22

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.

Accept starch

Question 23

Describe the transport of carbohydrate in plants.

Answer 23

1. Sucrose actively transported into phloem (cell);
   OR
   Sucrose is co-transported/moved with H+
   into
   phloem (cell);
2. (By) companion/transfer cells;
3. Lowers water potential (in phloem) and water
   enters (from xylem) by osmosis;
4. ((Produces) high(er) (hydrostatic) pressure;
   OR
   (Produces hydrostatic) pressure gradient;
5. Mass flow to respiring cells
   OR
   Mass flow to storage tissue/organ;
6. Unloaded/removed (from phloem) by active
   transport;