3.1 Gas Exchange

Question 1

What makes the lungs well adapted for gas exchange (diffusion): (6)

Answer 1

• Many alveoli provide a large surface area
• Many capillaries provide a large surface area
• Alveoli and capillary walls are thin
• This is due to the squamous (flattened) epithelial cells
• So there is a short diffusion pathway between the alveoli and the blood
• Ventilation brings fresh air into the lungs containing a high concentration of oxygen and removes
• air with a low concentration of oxygen
• Circulation keeps the blood moving so there is deoxygenated blood in contact with the alveoli
• This maintains a concentration gradient between the alveoli and the blood
• So fast rate of diffusion

Question 2

What are spiracles? (2)

Answer 2

• pores on surface of insect
• let gases in and out open and close by valves

Question 3

Advantages of tracheoles

Answer 3

• Many tracheoles
• highly branched
• larger surface area higher & rate of diffusion
• Short diffusion pathway.
• close to respiring cells.

Question 4

in insects…

Function of abdominal pumping.

Answer 4

• Ventilation by abdominal pumping brings in more oxygen rich air,
• so concentration of O2 is always higher at the start of tracheae compared to tracheoles
• maintains greater concentration gradient.

Question 5

Describe how oxygen enters during exercise of an insect.

Answer 5

• Oxygen rich air enters the spiracles down a pressure gradient
• oxygen travels along the trachea and along the tracheoles by diffusion
• down its diffusion gradient
• oxygen diffuses from the tracheoles into respiring cells
• down a concentration gradient.

Question 6

Why is abdominal pumping beneficial during increased activity?

Answer 6

• More oxygen enters more quickly
• To maintain a greater concentration/diffusion gradient between respiring cells and tracheoles

Question 7

Describe how surface area is optimised in fish.

Answer 7

lots of gill filaments
have lots of lamellae
increased SA for gas exchange

Question 8

Describe how concentration gradient is optimised in fish.

Answer 8

• Large number of capillaries inside the lamellae
• so blood always has a lower concentration of oxygen
• compared to the water it’s next to

Question 9

Describe the steps of ventilation, (irrigation) in fish.

Answer 9

1. mouth opens and a opercular valve shuts.
2. pressure decreases.
3. Mouth closes and a operculum valve opens.
4. Increased pressure forces water over gills and out.
5. Water enters the mouth.
6. Volume increases and the floor of the mouth is lowered.
7. Volume decreases and the floor of the mouth is raised.
8. Pressure increases.

Question 10

Fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange. (6)

Answer 10

1. Large surface area provided by lamellae/filaments;
2. Increases diffusion/makes diffusion efficient;
3. Thin epithelium/distance between water and blood;
4. Water and blood flow in opposite directions/countercurrent;
5. (Point 4) maintains concentration gradient (along whole gill lamella)/equilibrium not reached;
6. As water always next to blood with lower concentration of oxygen;
7. Circulation replaces blood saturated with oxygen;
8. Ventilation replaces water (as oxygen removed);

Question 11

What is the benefit of the counter current flow mechanism?

Answer 11

• Blood and water flow in opposite directions
  sO…
• the water next to the blood in the gill always has a higher concentration of oxygen.
• So diffusion can occur across the whole gill lamella
• This means that more oxygen will diffuse into the blood

Question 12

Water containing dissolved oxygen flows over the gill in the opposite direction to the blood flow inside. Explain why this arrangement is important for efficient oxygen uptake (2)

Answer 12

MP1 diffusion gradient will be maintained all the way along the gill

OR the amount of oxygen in the water is always higher than in the blood

MP2 more oxygen will diffuse into the blood

Question 13

Explain five ways in which an insect tracheal system is adapted for efficient gas exchange. (5)

Answer 13

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 diffusion
4. Trachea 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 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 14

Arteries and arterioles take blood away from the heart. Explain how the structure of the walls of arteries and arterioles are related to their functions: (6)

Answer 14

Elastic tissue (in the arteries)
* elastic tissue stretches under pressure/ventricular contraction
* recoils back
* prevents large fluctuations in pressure

Muscle (in arteriole)
* muscle contracts
* lumen is narrowed
* changes/reduces blood flow

Endothelium:
* endothelium is smooth
* reduces friction/chance of blood clots

Question 15

How does the rate of blood flowing change from the arteries to capillaries? (4)

Answer 15

• BF decreases
• total cross sectional area increases
• lumen narrower
• increased friction betw/ blood & blood vessel wall

Question 16

Suggest why pulse felt can be a measure of heart rate (2)

Answer 16

• pulse felt is the pressure
• caused by a ventricular contraction

Question 17

Why does the pressure of blood decrease from arteries to capillaries? (4)

Answer 17

• inc. total cross sectional area
• inc. friction
• dec. velocity
• fewer RBC’s able to flow through

Question 18

What happens to the artery walls in ventricular systole and what is the effect? (3)

Answer 18

• artery wall strecthes
• becomes thinner
• prevents pressure getting too high

Question 19

What happens in ventricular diastole and what is the effect? (3)

to the arteries

Answer 19

• artery wall recoils
• becomes thicker
• prevents large decrease in pressure

Question 20

Explain how the elastic tissue in the artery helps to reduce fluctuations in blood pressure. In terms of diastole. (5)

Answer 20

• arteries recoil and get thicker
• decr. size of lumen
• decr. volume in artery
• incr. pressure
• so smaller reduction in blood pressure

Question 21

When the smooth muscle in arterioles relax: (3)

Answer 21

• arterioles are dialated
• lumen becomes wider
• blood flow increases

Question 22

Describe the difference in composition of gases in inhaled and exhaled air. Explain how these differences are caused. (6)

Answer 22

INHALED AIR
* contains more oxygen than exhaled air
* contains less CO2 than exhaled air
* contains less water vapour
* relative percentage of nitrogen also changes
* respiration results in lower blood oxygen
* oxygen enters blood
* by diffusion
* water vapour diffuses from moist surface

Question 23

What adaptations do capillaries have to maximise gas exchange (6)

Answer 23

1.Permeable membrane;
2.Walls are single cell thick which means short diffusion pathway
3.Flattened (endothelial) cells which means short diffusion pathway;
5.Narrow lumen, reduces flow rate giving more time for diffusion;
6.Red blood cells are in contact with wall which gives short DP;
7.Fenestrations allows molecules through

Question 24

Give two differences in structure between aorta and the vena cava (2)

Answer 24

• Aorta has thicker wall (than vena cava)
• Aorta has a narrower lumen (than the vena cava)
• Aorta contains more/thicker (smooth) muscle (than the vena cava)
• Aorta contains more/thicker elastic tissue (than the vena cava)
• Vena cava has valves along its length but aorta only has semi-lunar valves

Question 25

Explain what happens when blood moves from arteriole end to venous end and how lymph fluid is formed and drained (6)

Answer 25

1. (hydrostatic) pressure of blood high at arterial end; (hp>op) 2. fluid/water/soluble molecules pass out (reject plasma); 3. proteins/large molecules remain; 4. this lowers the water potential (op>hp) 5. water moves back into venous end of capillary (reject tissue fluid); 6. by osmosis / diffusion; 7. lymph system collects any excess tissue fluid; 8. (lymph) returns to blood

Question 26

Describe and explain how water is exchanged between the blood and tissue fluid as blood flows along the capillary (4)

Answer 26

* HP forces water out; * HP is higher than OP * proteins remain in blood (increases WP gradient); * idea that OP is now "higher" than HP; * water returns by osmosis / along WP gradient; * water moves out at arteriole end and back in (at venule end);

Question 27

What causes the high hydrostatic pressure in the arteriole end?

Answer 27

(left) ventricular contractions

Question 28

In children, some diets may result in a low concentration of protein in the plasma. This can cause the accumulation of tissue fluid. Explain the link between a low concentration of protein in plasma and the accumulation of tissue fluid. (3)

Answer 28

* Water potential (in capillary) not as low / water potential gradient is reduced; * More tissue fluid formed (at arteriole end); * Less water **absorbed** (into blood capillary) by osmosis;

Question 29

Where in the body does haemoglobin load / unload O2?

Answer 29

* loads in the lungs * unloads in the respiring cells

Question 30

# Haemoglobin assosiation Binding to the first O2 changes the...

Answer 30

tertiary structure of the HG * this uncovers another haem group for the O2 to bind to * so HG affinity for O2 increases * easier to pick up next 2 O2 molecules * called: co-operative binding

Question 31

Explain how O2 is loaded, transported and unloaded in the blood (6)

Answer 31

* Haemoglobin carries oxygen / has a high affinity for o2 * In red blood cells; * Loading in lungs; * at high p.O2 * Unloads O2 to respiring cells/tissues; * at low p.O2 (where HG has low affinity for O2)

Question 32

How is fetal HG different to adult HG? | structure

Answer 32

* different primary structure (2 gamma chains instead of 2 beta chains) * different R groups in different places * different ionic/ h/ disulf form in different places * so different tertiary structure

Question 33

# fetal v adult HG p.O2 v % saturation of HG w/ O2 Which HG has a higher affinity for O2 and what is the advantage of this?

Answer 33

* fetal HG has higher affinity for O2 * so it can load more O2 at same p.O2 from adult HG and so adult will unload more O2 * so O2 can move from the mother to the foetus

Question 34

Describe the Bohr effect on haemoglobin (at high CO2 concentrations): (4)

Answer 34

* CO2 dissolves in blood as carbonic acid -> **changes charges on R groups** * **distorts bonds** * changes tertiary structure * HG has lower affinity for O2

Question 35

Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta: (6)

Answer 35

* atrium has **higher pressure than** ventricle (due to filling) **causing** atrioventricular valve **to open** * vetricle has higher pressure than atrium (due to filling) **causing** atrioventricular valve to close * ventricle has higher pressure than aorta causing the **semilunar** valve to open * pressure higher in aorta than ventricle causing semilunar valve to close * **ventricular contraction** causes higher pressure

Question 36

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

Answer 36

* Named structures – trachea, bronchi, bronchioles, alveoli; * Breathing in – diaphragm contracts and **external** intercostal muscles contract; * (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in); * Breathing out - Diaphragm relaxes and internal intercostal muscles contract; * (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);

Question 37

Explain 6 ways in which an insects tracheal system is adapted for efficient gas exchange (during excercise): (6)

Answer 37

1. Tracheoles have thin walls so short diffusion distance to cells; 2. Large number of tracheoles so short diffusion distance to cells; 3. 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; 6. Body can be moved (by muscles) to move air so maintains diffusion gradient for O2/ CO2

Question 38

Why do damselfy larvae need gills but other species that also live in water not need gills? (2)

Answer 38

* damselfy larvae have a higher metabolic rate * so they need more O2 per unit mass

Question 39

Tissue fluid is formed from blood at the arterial end of the capillary bed. Explain how water from the tissue fluid is returned to the circulatory system. (4)

Answer 39

1. (Plasma) proteins remain; 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 40

Mackrel is fast but toad swim slowly Mackrel have thinner gills and more lamellae per gill. Explain how they are able to swim faster: (3)

Answer 40

* large numbers of lamellae so large SA; * lamellae thin so short (diffusion) pathway to capillaries; * high rate of oxygen uptake for respiration;

Question 41

Describe and explain how the structure of the mamallian breathing system enables efficient o2 uptake into the blood (6)

Answer 41

1. alveoli provide a large surface area; 2. walls of alveoli thin to provide a short diffusion pathway; 3. walls of capillary thin / close to alveoli provides a short diffusion pathway; 4. walls (of capillaries / alveoli) have flattened cells; 5. cell membrane permeable to gases; 6. many blood capillaries provide a large surface area; 7. diaphragm muscles maintain a diffusion gradient; 8. **wide trachea for efficient flow of air;** 9. **cartilage rings keep airways open;**

Question 42

equation for pulmonary ventilation

Answer 42

PV = BR X TV dm^3

Question 43

Suggest and explain one way the leaf growth of Xerophytic plants would be different from the leaf growth of sunflowers.

Answer 43

* Growth will be slower * fewer stormata for gas exchange