1. What is the primary function of gas exchange in animals ?
Answer
To obtain oxygen for respiration and get rid of carbon dioxide.
2. Terrestrial insects have an exoskeleton that is fairly rigid and coated with a waxy substance. This makes their surface waterproof, which is important to ensure they do not dry out. However, this means that gas exchange through simple diffusion through the body surface, such as with single-celled organisms, is not possible. Describe how insects have evolved to overcome this.
Answer
They have evolved a series of openings called spiracles, which lead to a series of tubes called tracheae and then tracheoles.
3. Insects have evolved to have a series of openings leading to a network of tubes that are able to transport oxygen to their tissues and organs around their body. Describe the pathway of oxygen from the surrounding air to the cells, naming the structures that are involved.
Answer
Oxygen enters via the spiracles on the surface of the insect. Travels down the tracheae. Continues down the tracheoles until it reaches the tissues.
4. The figure below shows the relationship between pleural pressure, alveolar pressure and change in lung volume. Pleural pressure is the pressure within the cavity surrounding the lung. Describe the relationship between the three different graphs.
Answer
As pleural pressure decreases, lung volume increases. Alveolar pressure has an intermediate pattern, decreasing and then returning to original state.
5. Use your understanding of pulmonary ventilation to explain the changes that occur in the figure above.
Answer
Lung volume increases because thoracic pressure decreases. This occurs when the diaphragm contracts and the external intercostal muscles contract. Once the pressure inside the thorax is lower than atmospheric pressure, air enters the alveoli, causing the pressure to return to 0. Alternatively, lung volume decreases because thoracic pressure increases. This happens when the diaphragm relaxes and the internal intercostal muscles contract. Once the pressure inside the thorax is higher than atmospheric pressure, air leaves the alveoli, causing the pressure to return to 0.
6. Name the term given to the interaction between internal and external intercostal muscles, and explain what this term means.
Answer
Antagonistic: when one muscle contracts, the other relaxes.
7. There is a counter-current flow system in the gills of a fish. This achieves efficient gas exchange. Explain how.
Answer
Water and blood flow in opposite directions, which maintains a concentration gradient along the entire length of the lamellae.
8. A fish has a mass of 260 g. It needs 4580 mg of oxygen per kg of body mass per day. The water contains 8.93 mg of oxygen per dm3. Assume that the fish gills absorb 70% of the dissolved oxygen from the water. Calculate the volume of water in dm3 that passes through the fish gills in one hour to supply the fish with the oxygen it needs.
Answer
Fish needs (4580/24) × (260/1000) = 49.62 mg oxygen per hour.
Fish absorbs 70/100 × 8.93 = 6.25 mg of oxygen per dm3
49.62/6.25 = 7.94 dm3 (water passing through gills in 1 hour)
9. The value you calculated above would be higher if the temperature was increased by 3°C. Give two reasons why.
Answer
Oxygen is less soluble in warmer water. Enzyme activity increases with temperature so more oxygen needed for respiration.