gas exchange

Question 1

How does oxygen move through the insect?

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.

Answer 2

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);
4. 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;

Question 3

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

Answer 3

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

Question 4

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

Answer 4

1 Large surface area provided by many lamellae over many gill 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 gill)/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 5

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

Answer 5

1. Named structures – trachea, bronchi, bronchioles, alveoli;
2. Above structures named in correct order OR Above structures labelled in correct positions on a diagram;
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);
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);

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) via stomata;
2. (Stomata opened 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

Answer 7

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