1. Larger organisms need specialised gas exchange organs, but single-celled organisms like Chlamydomonas do not. Explain why.
Answer
The diffusion distance in a larger organism is too great; therefore it would take too long for oxygen to diffuse into larger organisms, so cells would die as a result.
2. In the lungs of humans, each bronchiole ends in a cluster of alveoli. The alveoli are surrounded by a network of capillaries. Explain how a good blood supply ensures that gas exchange in the lungs is efficient.
Answer
A good blood supply maintains a high concentration gradient, which is needed for efficient diffusion/gas exchange to take place. It also increases the surface area for gas exchange to take place.
3. The figure below shows the flow of water and blood in a gill filament. The numbers indicate the relative concentration of oxygen in the water and in the blood. Explain how this ensures efficient gas exchange between the blood and the water.
Answer
Water flows in opposite direction to blood flow. This is called the counter-current system. Ensures that the oxygen concentration is always higher in the water than in the blood. This means that oxygen will continuously diffuse into the blood across the gill membrane.
4. The figure below shows the changes in breathing rate and depth of breathing of a person as they change the activity that they are doing. Calculate the pulmonary ventilation rate (PVR) of this person when they are at rest.
Answer
The breathing rate is identified as 12 breaths per minute, and the tidal volume is identified as 0.5 dm3. Therefore, pulmonary ventilation rate
5. Between B and C the person is exercising. Explain the changes that occur in their breathing.
Answer
As the person begins to exercise, their breathing rate increases and becomes faster. The depth of breathing (tidal volume) also increases. This allows gas exchange to occur more rapidly, so that more oxygen reaches the muscles to support increased aerobic respiration.
6. A scientist measured the gas exchange in a resting frog. The table below shows the results. Calculate the percentage of gas exchange that is occurring through the skin.
Answer
0.34/(0.34 + 1.80) × 100 = 15.9%
7. Fireflies are insects that are active at night. They are able to produce light signals using ATP. This is called bioluminescence. Fireflies have light organs that are surrounded by tracheoles. Organs inside the tracheoles contain chemicals that will produce bioluminescence but only in the presence of oxygen. The figure below shows the light-producing organs and the tracheoles when a firefly is not producing light, and the same structures when light is being produced. Describe the changes that occur in the tracheoles when the firefly is producing light.
Answer
Fluid in tracheole decreases when fireflies emit bioluminescence.
8. Explain how these changes help the firefly to produce light.
Answer
Water potential in surrounding cells and light organs decreases. Water moves by osmosis from tracheoles into surrounding cells. Oxygen is able to diffuse into cells allowing reactants to emit bioluminescent signals.
9. The figure below shows the gas exchange system of a bird. The arrows show the flow of air through the respiratory system. The gas exchange system of a bird is more efficient at extracting oxygen from inhaled air than the human gas exchange system. Explain how.
Answer
In birds, air flows in one direction with very little or no mixing of inhaled and exhaled air. This maintains a concentration gradient along the gas exchange surfaces, allowing more time for efficient gas exchange.
10. The lungs of a bird are filled with tiny tubes called parabronchi through which air flows. The parabronchi have many capillaries in their lining. Explain how the presence of parabronchi improves the efficiency of gas exchange.
Answer
Greater surface area for gas exchange.