Topic 3 - Organisms exchange substances EXAM QUESTIONS

Question 1

Explain the advantage for larger animals of having a specialised system
that facilitates oxygen uptake. (2)

Answer 1

1. Large(r) organisms have a small(er) surface area: volume (ratio);
   OR
   Small(er) organisms have a large(r) surface area: volume (ratio);
2. Overcomes long diffusion pathway OR
   Faster diffusion;

Question 2

Mammals such as a mouse and a horse are able to maintain a constant
body temperature.
Use your knowledge of surface area to volume ratio to explain the higher
metabolic rate of a mouse compared to a horse. (3)

Answer 2

Mouse
1. (Smaller so) larger surface area to volume ratio;
Accept larger SA:V.
Must be comparative.
2. More/faster heat loss (per gram/in relation to body size);
Ignore heat lost more easily/readily.
Must be comparative.
3. (Faster rate of) respiration/metabolism releases heat;
Accept respiration/metabolism replaces heat.
Reject produce/generate heat/energy.

Question 3

Explain why oxygen uptake is a measure of metabolic rate in organisms. (1)

Answer 3

(Oxygen used in) respiration, which provides energy / ATP;
OR
(Oxygen is used in) respiration, which is a metabolic process /
chemical reaction;

Question 4

Describe and explain one feature of the alveolar epithelium that makes the
epithelium well adapted as a surface for gas exchange. Do not refer to
surface area or moisture in your answer. (2)

Answer 4

Mark in pairs: 1 and 2 OR 3 and 4
1. Flattened cells
OR
Single layer of cells;
Reject thin cell wall/membrane
Accept thin cells
Accept ‘one cell thick’
2. Reduces diffusion distance/pathway;
3. Permeable;
4. Allows diffusion of oxygen/carbon dioxide;

Question 5

Explain how the counter-current principle allows efficient oxygen uptake in
the fish gas exchange system. (2)

Answer 5

1. Blood and water flow in opposite directions;
2. Diffusion/concentration gradient (maintained) along
   (length of) lamella/filament;

Question 6

Describe and explain the mechanism that causes lungs to fill with air. (3)

Answer 6

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 7

Particulate matter is solid particles and liquid particles suspended in air.
Polluted air contains more particulate matter than clean air.
A high concentration of particulate matter results in the death of some
alveolar epithelium cells. If alveolar epithelium cells die inside the human
body they are replaced by non-specialised, thickened tissue.
Explain why death of alveolar epithelium cells reduces gas exchange in
human lungs. (3)

Answer 7

1. Reduced surface area;
2. Increased distance for diffusion;
   Accept description of efficient gas exchange in
   healthy alveolar epithelium as long as reference
   made to the damaged tissue changing this.
3. Reduced rate of gas exchange;

Question 8

Use your knowledge of gas exchange in leaves to explain why plants
grown in soil with very little water grow only slowly. (2)

Answer 8

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

Question 9

Describe the pathway taken by an oxygen molecule from an alveolus to the
blood. (2)

Answer 9

1. (Across) alveolar epithelium;
2. Endothelium / epithelium of capillary;

Question 10

Explain how one feature of an alveolus allows efficient gas exchange to
occur. (2)

Answer 10

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

Question 11

Describe the gross structure of the human gas exchange system and how
we breathe in and out.
(6)

Answer 11

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;
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 12

Explain three ways in which an insect’s tracheal system is adapted for
efficient gas exchange. (3)

Answer 12

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 13

Explain two ways in which the structure of fish gills is adapted for efficient
gas exchange. (2)

Answer 13

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

Question 14

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

Answer 14

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 15

The movement of Na+ out of the cell allows the absorption of glucose into
the cell lining the ileum.
Explain how. (2)

Answer 15

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;

Question 16

Describe the role of micelles in the absorption of fats into the cells lining
the ileum. (3)

Answer 16

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

Question 17

Describe the role of enzymes in the digestion of proteins in a mammal. (4)

Answer 17

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 18

Explain the advantages of lipid droplet and micelle formation (3)

Answer 18

1. Droplets increase surface areas (for lipase /
   enzyme action);
2. (So) faster hydrolysis / digestion (of
   triglycerides / lipids);
3. Micelles carry fatty acids and glycerol /
   monoglycerides to / through membrane / to
   (intestinal epithelial) cell;

Question 19

Cells lining the ileum of mammals absorb the monosaccharide glucose by
co-transport with sodium ions. Explain how. (3)

Answer 19

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 20

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. (3)

Answer 20

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

Question 21

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 (4)

Answer 21

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 22

Describe the advantage of the Bohr effect during intense exercise. (2)

Answer 22

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 23

Describe and explain the effect of increasing carbon dioxide concentration
on the dissociation of oxyhaemoglobin. (2)

Answer 23

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;

Question 24

Binding of one molecule of oxygen to haemoglobin makes it easier for a
second oxygen molecule to bind.
Explain why. (2)

Answer 24

1. Binding of first oxygen changes tertiary / quaternary (structure) of
   haemoglobin;
   Ignore ref. to ‘positive cooperativity’ unqualified
   Ignore ref. to named bonds
   Accept conformational shift caused
2. Creates / leads to / uncovers second / another binding site
   OR
   Uncovers another iron / Fe / haem group to bind to;

Question 25

Explain the role of the heart in the formation of tissue fluid. (2)

Answer 25

1. Contraction of ventricle(s) produces high
   blood / hydrostatic pressure;
2. (This) forces water (and some dissolved
   substances) out (of blood capillaries);