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 (6)

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;
   OR
   Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);
5. Body can be moved (by muscles) to move air so maintains 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 (3)

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 (8)

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. 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 (4)

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 (2)

Answer 7

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

Question 8

What limits water loss in insects? (2)

Answer 8

• Waterproof coating - rigid outerskeleton covered with waterproof cuticles
• Small SA:V raio - minimise area which water is lost

Question 9

Adaptation of leaf for gaseous exchange (3)

Answer 9

• Flat - gives large SA:V ratio
• Many stomata - pores allow air to move in and out of leaf
• Air spaces in leaf = short diffussion distance between mesophyll + air

Question 10

Diffusion of CO2 for photosynthesis - plants (4)

Answer 10

1. Mesophyll cell photsyntesis = reduce conc of Co2 in cell
2. CO2 diffuses from air space into cell
3. Reduces CO2 conc in air spaces
4. Co2 moves inti air spaces from outside lead through stomata

Question 11

Diffusion of O2 - plants (2)

Answer 11

1. Mesophyll cells produce O2 result of photsynthesis
2. O2 diffuses into air spaces from cell
3. Increases conc of O2 in air spaces
4. O2 moves from air spaces to outside the leaf via stomata

Question 12

Adaptations of plants to reduce water loss (3)

Answer 12

1. At night guard cells close stomata to prevent water loss = less CO2 needed at night due to lack of sunlight for photosynthesis
2. Upper + lower surface = waxy cuticle
3. Most stomata found on lower surface

Question 13

Adaption of Xerophytic plants to reduce water loss (6)

Answer 13

1. Reduced num of stomata = less surface area
2. Stomata in pits = reduced conc gradient
3. Hair trap water vapour = reduced conc gradient
4. Rolled leaves = reduced conc gradient
5. Leaves reduced to spines = less SA for water loss
6. Thicky waxy cuticles = increased diffusion distance

Question 14

Why does Oxygen diffusion occurs in insects (4)

Explain every step

Answer 14

1. Tissue respires using O2 reducing conc of O2 in tissue
2. O2 moves from area of high conc to area of low conc
3. So O2 moves from Tracheae to tissues
4. Lowers O2 conc in trachea so O2 moves into tracheae via the spiracles

Question 15

Why does diffusion happen in insects - Carbon dioxide (3)

Explain

Answer 15

1. Respiration produced CO2 = increases conc of Co2 at tissue
2. Co2 moves from area of high conc in tissue to area of low conc in Tracheae
3. Co2 moves from high conc in Tracheae to low conc outside insect via spiracles

Question 16

Diffusion rate

Answer 16

SA x conc gradient / diffusion distance