gas exchange

Question 1

How does oxygen move through the insect?

Answer 1

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

Question 2

Explainthreeways in which an insect’s tracheal system is adapted for efficient gas exchange.

Answer 2

1. Tracheoles have thin wallssoshort diffusion distance to cells;
   2.Highly branched / large number of tracheolessoshort diffusion distance to cells;
2. Highly branched / large number of tracheolessolarge surface area (for gas exchange);
   4.Tracheae provide tubes full of airsofast diffusion (into insect tissues);
   5.Fluid in the end of the tracheoles that moves out (into tissues) during exercisesofaster diffusion through the air to the gas exchange surface;
   OR
   Fluid in the end of the tracheoles that moves out (into tissues) during exercisesolarger surface area (for gas exchange);
3. Body can be moved (by muscles) to move airsomaintains diffusion / concentration gradient for oxygen / carbon dioxide;

Question 3

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

Answer 3

. Water and blood flow in opposite directions;
. Maintains diffusion/concentration gradient of oxygen OR Oxygen concentration always higher (in water);
. (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

. Large surface area provided by many lamellae over many gill filaments;
. Increases diffusion/makes diffusion efficient;
. Thin epithelium/distance between water and blood;
. Water and blood flow in opposite directions/countercurrent;
. (Point 4) maintains concentration gradient (along gill)/equilibrium not reached;
. As water always next to blood with lower concentration of oxygen;
. Circulation replaces blood saturated with oxygen;
. 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

. Named structures – trachea, bronchi, bronchioles, alveoli;
. Above structures named in correct order OR Above structures labelled in correct positions on a diagram;
. 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 6

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

Answer 6

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

Question 7

Explain why plants grown in soil with very little water grow only slowly.

Answer 7

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