Gas Exchange

Question 1

How does oxygen move through the insect? (4)

Answer 1

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

Question 2

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

Answer 2

1. Tracheoles have thin walls SO short diffusion distance
2. Highly branched SO short diffusion distance
3. Highly branched SO large surface area
4. Tracheae provide tubes full of air SO fast diffusion

Question 3

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

Answer 3

1. Water and blood flow in opposite directions
2. Maintains diffusion / concentration gradient of oxygen
3. Along length of lamellae / filament / gill

Question 4

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

Answer 4

1. Many filaments SO large surface area
2. Thin lamellae FOR short diffusion pathway

Question 5

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange. (5)

Answer 5

1. Large surface area provided by many lamellae over many gill filaments
2. Increases diffusion
3. Thin distance between water and blood
4. Water and blood flow in opposite directions
5. Maintains concentration gradient (follow on from point 4)
6. Water is always next to blood with lower concentration of oxygen
7. Circulation replaces blood saturated with oxygen
8. Ventilation replaces water

Question 6

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

Answer 6

1. Carbon dioxide enters through stomata
2. Stomata opens by guard cells
3. Diffuses through air spaces
4. Down diffusion gradient

Question 7

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

Answer 7

1. Stomata close
2. Less carbon dioxide uptake so less photosynthesis

Question 8

Explain the movement of oxygen into the gas exchange system of an insect when it is at rest (3)

Answer 8

1. Oxygen used in (aerobic) respiration
2. Oxygen concentration gradient established
3. Oxygen diffuses in; 2 and 3.

Question 9

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. Details of breathing are not required (4)

Answer 9

1. Pass through trachea, into bronchi, into bronchioles
2. Down pressure gradient
3. Down diffusion gradient
4. Across alveolar epithelium
5. Across capillary endothelium

Question 10

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

Answer 10

1. Across alveolar epithelium
2. Across endothelium of capillary

Question 11

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

Answer 11

1. One cell thick
2. So short diffusion distance

Question 12

Explain why death of alveolar epithelium cells reduces gas exchange in human lungs (2)

Answer 12

1. Reduced surface area
2. Increased distance for diffusion

Question 13

Describe inhalation (5)

Answer 13

1. External intercostal muscles contract pulling rib cage up and out
2. Diaphragm contracts and pulls down
3. Thoracic cavity volume increases
4. Pressure in lungs lower than atmospheric pressure
5. Air moves into lungs down a pressure gradient

Question 14

Describe exhalation (5)

Answer 14

1. External intercostal muscles relax
2. Diaphragm relaxed and moves up
3. Thoracic volume decreases
4. Pressure in lungs greater than atmospheric pressure
5. Air moves out of lungs down a pressure gradient

Question 15

Describe the pathway of oxygen from the atmosphere to the blood (6)

Answer 15

1. Pass through trachea
2. Enter bronchi, leading to bronchioles
3. Enter alveoli
4. Squamous epithelial cell
5. Capillary endothelial membrane
6. Red blood cell membrane

Question 16

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

Answer 16

1. Trachea, into bronchi, into bronchioles, into alveoli
2. (Above structures named in correct order)
3. Breathing in - diaphragm contracts and external intercostal muscles contract
4. Causing thoracic cavity volume to increase and pressure decrease
5. Breathing out - diaphragm relaxes and internal intercostal muscles contract
6. Causes thoracic cavity volume to decrease and pressure increase