1. What is the relationship between the size of an organism and its surface area to volume ratio ?
Answer
As the organism gets bigger, their surface area to volume ratio gets smaller.
2. The blood system in the lamellae of fish gills is arranged to allow water to flow in the opposite direction to the blood flow. Name this process and explain why it is an advantage to the fish.
Answer
Counter-current system. This ensures that there is a concentration gradient all the way along the lamellae.
3. During times of vigorous movement, such as flying, changes occur at the ends of the tracheoles. The figure below shows these changes. Describe and explain these changes, and explain why it is advantageous for this to happen during flight.
Answer
During flight, the insect respires anaerobically, producing lactate. Lactate lowers the water potential of the cell's cytoplasm, causing water to be drawn into the muscle cells. This reduces the diffusion distance for oxygen into the muscle cells. Oxygen can then be used for aerobic respiration, providing ATP for movement and muscle contraction. As a result, the insect is able to obtain more oxygen for aerobic respiration.
4. Describe and explain the relationship between the two graphs below.
Answer
As the pressure decreases during inspiration, the volume of air in the lungs increases because the volume of the thorax has expanded due to the contraction of the diaphragm and external intercostal muscles. During expiration, the pressure increases and the volume of air in the lungs decreases because the volume of the thorax has reduced due to the relaxation of the diaphragm and the contraction of the internal intercostal muscles.
5. A mammalian heart is more efficient than that of an amphibian. Explain why.
Answer
Amphibians have only one ventricle, whereas mammals have two. As a result, oxygenated and deoxygenated blood mix and are not kept fully separated in amphibians.
6. The table below shows data for different kinds of marine fish. The gill area is measured in mm2 per gram of fish. Explain why mm2 per gram is used.
Answer
Fish vary in size. Measuring in mm2 per gram allows comparison.
7. Describe and explain the relationship between the activity level of the fish and the data for the filaments and lamellae.
Answer
Number of filaments, length of filaments and number of secondary lamellae per mm all increase with activity. Increases surface area for gas exchange. More active fish need more oxygen for aerobic respiration.
8. Birds that live in cold environments, such as certain species of duck, may spend a long time standing on ice. This means they can lose a great deal of body heat through their feet. It is important that blood flow is maintained to the cells in their feet or the cells will die. The figure below shows the position of the artery and vein in a duck's foot. The artery and vein run very close to each other. There are sphincter (ring) muscles that control blood flow. Explain how the circular muscle in the artery enables the duck to lose as little body heat as possible when standing on ice.
Answer
The circular muscle in the artery slows or reduces blood flow from the body to the leg, giving more time for heat transfer from the artery to the veins.
9. The table below shows the changes in temperature in both blood vessels of a duck. Use your understanding of the counter-current system to explain how birds are able to use this mechanism to be able to survive in such cold climates.
Answer
Arterial blood is warm as it comes from the core. As it flows down the leg, there is a large temperature difference between the artery and the vein. Heat from the artery is transferred to the vein, warming the blood before it returns to the core. By the time the arterial blood reaches the feet, it has cooled, meaning less heat is lost to the environment.