Module 3 - Gas Exchange

Question 1

4 marks

Decsribe fish ventillation

Answer 1

1. Mouth opens, opercular valve shuts
2. Floor of mouth lowered
3. Water enters due to decreased pressure, increased volume
4. Mouth closed, opercular valave opens
5. Floor of mouth raised= increased pressure, decreased volume
6. Increased pressure pushes water over gills

Question 2

4 marks

Describe expiration

Answer 2

1. Contraction of internal intercostal muscles
2. Relaxation of diaphragm muscles and external intercostal muscles
3. Causes decrease in thoracic cavity
4. Air pushed down pressure gradient

Question 3

How does asthma affect the mean volume of air breathed out

Answer 3

1. Muscle walls of bronchi/bronchioles contract;
2. Walls of bronchi/bronchioles secrete more mucus;
3. Diameter of airways reduced;
4. (Therefore) flow of air reduced;

Question 4

3 marks

Describe how gas exchange occurs in single-celled organisms and explain why this method cannot be used by large, multicellular organisms.

Answer 4

1. Diffusion (across the cell surface membrane);
2. Large organisms have small(er) sa : vol ratio
3. Diffusion pathway would be too long

Question 5

3 marks

Describe and explain the importance of three adaptation of the gas exchange surface in the tracheal system of an insect

Answer 5

1. Tracheole (wall) thin/one cell thick;
2. (So) rapid diffusion (into cells)
3. Tracheoles enter/supply tissues/muscle fibres;
4. (So) diffusion direct into cells
5. Tracheoles are highly branched;
6. (So) large surface area for (rapid) diffusion;

Question 6

6 marks

Describe how the structure of the insect gas exchange system:
*   provides cells with sufficient oxygen
*   limits water loss.

Answer 6

1. Spiracles, tracheae, tracheoles;
2. Spiracles allow diffusion of oxygen
3. Tracheoles are highly branched so large surface area for exchange
4. Tracheole walls thin so short diffusion distance to cells
5. Tracheole walls are permeable to oxygen/air
6. Exoskeleton impermeable- covered with waterproof waxy cuticle so reduce water loss
7. Spiracles can close so less water loss
8. Hairs around spiracles reduce water loss

Question 7

5 marks

Describe how humans breathe in and out

Answer 7

Breathing in
1. Diaphragm muscles contract and diaphragm flattens
2. External intercostal muscles contract and ribcage pulled up
3. Increase in volume of thoraic cavity and pressure decreases
Breathing out
4. Diaphragm muscles relaxes and diaphragm becomes curved
5. External intercostal muscles relax and ribcage moves down
6. Decrease in volume of thoraic cavity and increase in pressure –> air pushed down pressure gradient

Question 8

3 marks

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

Answer 8

1. Tracheoles have thin walls so short diffusion distance to cells
2. Highly branched/ large no. of tracheoles so short diffusion distance to cells
3. Highly branched/ large no. of tracheoles so large SA
4. Tracheae provide tubes full of air so fast diffusion into insect tissues
5. Fluid in the end of tracheoles that move out into tissues during exercise so larer SA
6. Body can be moved by muscles to more air so maintains conc gradient for O2/CO2

Question 9

2 marks

The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain
oxygen from water. Explain how the presence of gills adapts the damselfly to its way of life

Answer 9

1. Damselfly has a higher metabolic/ respiratory rate
2. So uses more oxygen

Question 10

3 marks

Particulate matter is solid particles and liquid particles suspended in air. Polluted air contains more particulate matter than clean air. A high concentration of particulate matter results in the death of some alveolar epithelium cells. If alveolar epithelium cells die inside the human body they are replaced by non-specialised, thickened tissue.
Explain why death of alveolar epithelium cells reduces gas exchange in human lungs.

Answer 10

1. Reduced surface area
2. Increased distance for diffusion
3. Reduced rate of gas exchange