1. The figure below shows the human gas exchange system. Identify the labelled structures A–F.
Answer
A = Trachea,
2. Xerophytes are plants that live in conditions where there is very little fresh water. They have evolved adaptations to deal with this lack of water. Give some ways in which xerophytes can be adapted.
Answer
They may develop a thick cuticle to reduce water loss, have small or needle-shaped leaves, and possess very few stomata. In some species, the stomata are located in sunken pits and surrounded by hairs to minimize evaporation. Leaves can inroll to trap moisture, or be reduced to spikes with photosynthesis occurring in the stems instead. Additionally, many xerophytes grow extensive root systems to maximize water absorption from the soil.
3. The figure below shows the structure of a single gill. Identify X and Y.
Answer
X = Lamellae,
4. Explain how the arrangement of the gills above is an adaptation for efficient gas exchange.
Answer
Large surface area created. Good blood supply, maintaining concentration gradient.
5. The figure below shows the rate at which air is expelled from the lungs in a healthy person and a person with emphysema. There are differences in the way air is expelled from healthy lungs and from lungs with emphysema. Identify two of these differences.
Answer
Volume and rate of air leaving lungs is lower in emphysema.
6. Use the figure above to explain the difference in the rate at which air is breathed out between the healthy person and the person with emphysema.
Answer
The alveolar walls have been broken down, leading to a smaller surface area for gas exchange. As a result, less oxygen diffuses into the blood, causing an increased breathing rate. Additionally, the reduction in capillaries and the greater diffusion distance further impair gas exchange.
7. The figure below shows the main components of the circulatory system of a frog. Frogs have two gas exchange surfaces: the skin and the lungs. Gas exchange through the skin increases during a dive. Using your knowledge of circulatory systems to suggest how this occurs.
Answer
The heart rate increases, resulting in more blood flow through the skin capillaries and less blood flow through the pulmonary circuit. Arterioles dilate, allowing more blood to pass through the skin, while arterioles leading to the pulmonary vessels constrict. Additionally, the spiral valve in the heart may divert blood toward the skin to enhance gas exchange during the dive.
8. Scientists carried out an investigation to find out how much gas exchange occurs through the skin and the lungs in a frog during a dive. Their results are shown in the figure below. Total gas exchange falls during the dive and increases considerably after the dive. Explain why.
Answer
Skin gas exchange cannot increase enough to supply all the oxygen required. The lungs cannot be used for gas exchange during the dive, so more anaerobic respiration occurs. As a result, an oxygen debt builds up, leading to increased gas exchange after the dive when the lungs can be used again.
9. Gas exchange was measured per gram of body mass. Explain why.
Answer
Frogs vary in size, so measuring gas exchange per gram of body mass allows for comparison between frogs of different sizes.
10. Describe the relative importance of the lungs and skin in gas exchange when a frog is at rest.
Answer
The lungs carry out most of the gas exchange and are therefore the most important. Data show that gas exchange through the skin is about one-third of that through the lungs, or about one-quarter of the total gas exchange.