Gas Exchange 3.1-3.2

Question 1

What is the name given to the flow of blood through the lamellae of the gills?

Answer 1

Counter-current flow

Question 2

Why does counter-current flow increase amount of oxygen absorbed?

Answer 2

Water flows in the opposite direction to blood, maintaining the (constant) concentration difference across the gill lamellae.

Question 3

How is gas exchange increased in an insect? (3 points)

Answer 3

1. Abdominal muscles contract, moving air in and out to maintain a concentration gradient,
2. Branched tracheoles increase surface area,
3. Tracheoles have thin walls for short diffusion difference.

Question 4

How is a concentration gradient created in an insect?

Answer 4

Cellular aerobic respiration uses oxygen and creates carbon dioxide.

Question 5

Why are the ends of the tracheoles fluid filled?

Answer 5

During high intensity/strenuous respiration, the water moves into the muscles allowing:
- a greater surface area (for gas exchange)
- diffusion to happen as a gas rather than a liquid medium.

Question 6

How do fish gills use the counter-current system? BLURT

Answer 6

Fish gills use the counter-current system as blood flows in the opposite direction of the water moving over the gills lamellae, maintains (constant) concentration gradient.

The oxygen-rich fresh water enters the gills where the blood is leaving for the body. As it leaves the gills, low in oxygen, it passes by capillaries containing deoxygenated blood, maintains conc gradient.

Question 7

How do insects carry out gas exchange? BLURT

Answer 7

In an insect, the contraction of abdominal muscles moves air through the trachea and tracheoles and in and out of the spiracles.

Water is found at the end of the spiracles. During anaerobic respiration, the lactic acid produced draws the water into the muscle through water potential difference. This allows diffusion through gas rather than liquid when more oxygen is required.

Question 8

Pulmonary Ventilation Rate (PVR) =

Answer 8

PVR = Tidal Volume x breathing rate

(TV = Natural breathing rate)

Question 9

Fick’s Law =

Answer 9

Rate of diffusion = Surface Area x Concentration Gradient
/ Diffusion distance

Question 10

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

Answer 10

1. Named passage of oxygen through trachea -> bronchi -> bronchioles -> alveoli;
   (Lungs as human gas exchange surface)

Inhalation:
2. External intercostal muscles contract + diaphragm moves down (contracts) opening chest cavity;
3. Causes volume increase + pressure decrease in thoracic cavity;

Exhalation:
4. Internal intercostal muscles contract + Diaphragm relaxes;
5. Causing volume decrease + Pressure increase in lungs.

Question 11

Describe the pathway taken by an oxygen molecule from an alveolus to the blood [2]

Answer 11

1. Across alveolar/squamous epithelium;
2. To endothelium of capillary.

Question 12

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf (4)

Answer 12

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

Question 13

Explain why plants grown in soil with very little water grow only slowly (2)

Answer 13

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

Question 14

Describe how the movement of the diaphragm leads to air movement into the lungs

Answer 14

1. Diaphragm contracts and flattens;
2. Volume of lungs increases;
3. Presure inside the lungs is lower than atmospheric pressure;
4. Air moves into the lungs.

Question 15

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them

Answer 15

• Many alveoli / alveoli are folded - provides large surface area;
• Many capillaries provides large surface area so fast diffusion;
• Alveoli epithelium is 1 cell thick / thin so reduced/short diffusion distance (between alveoli and blood);
• Flattened/squamous epithelium so short diffusion distance / so fast diffusion;
• Ventilation/circulation so maintains a concentration/diffusion gradient so fast diffusion.

Question 16

Describe the gross structure of human gas exchange system and how we breathe in and out (5)

Answer 16

1. Named structures O2 IN - Trachea, Bronchi, Bronchioles, Alveoli
2. BREATHING IN/INHALATION - Diaphragm contract and external intercostal muscles contract, volume increase and pressure in thoracic cavity decrease;
3. BREATHING OUT/EXHALATION - Diaphragm relaxes and internal intercostal muscles contract, volume decrease and pressure increase in thoracic cavity.

Question 17

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

Answer 17

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

Question 18

How does oxygen move through an insect? (4)

Answer 18

1. Oxygen diffuses in through the spiracles;
2. Spiracle closes;
3. Oxygen moves through the trachea into the tracheoles;
4. Oxygen delivered directly to respiring tissues

Question 19

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange (5)

Answer 19

1. Tracheoles have thin walls so short diffusion distance;
2. Highly branched/many tracheoles so short diffusion distance AND large surface area;
3. Tracheae provides tubes full of air so fast diffusion;
4. Fluid in end of tracheoles moves into tissues during exercise so larger surface area;
5. Body moved by muscles so maintains diffusion/concentration gradient for O2/CO2

Question 20

Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill (3)

Answer 20

1. Water and blood flow in opposite directions;
2. Maintains diffusion/concentration gradient of O2 (always higher in water);
3. (Constant) Diffusion along lamellae/filament/gill.

Question 21

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

Answer 21

1. Large surface area as many lamellae over many gill filaments;
2. Makes diffusion efficient/increases diffusion;
3. Thin epithelium/short diffusion distance between blood and water;
4. Countercurrent/opposite flow of water and blood;
5. (so) maintains concentration gradient (as equilibrium not reached);
6. Water always next to blood with lower concentration of oxygen;
7. Circulation replaces blood saturated with oxygen;
8. Ventillation replaces water (as oxygen removed).