(a) Describe two ways in which the circulatory system of a fish is different from the circulatory system of a mammal.
(b) Explain the advantages of a double circulatory system.
(c) Fig. 5.1 shows part of the circulatory system of a mammal.
(i) State the letter from Fig. 5.1 that identifies where these processes occur:
absorption of the products of digestion into the blood
excretion of carbon dioxide from the body
formation of urine
production of bile.
(ii) Identify the name of the blood vessel labelled X in Fig. 5.1.
(d) Describe the role of the liver in excretion.
▶️ Answer/Explanation
(a)
1. Fish have single circulation (blood flows through the heart once per body circuit) while mammals have double circulation (blood flows through the heart twice per body circuit).
2. Fish hearts have two chambers (one atrium and one ventricle) while mammalian hearts have four chambers (two atria and two ventricles).
3. Fish hearts have no septum (allowing mixing of oxygenated and deoxygenated blood) while mammalian hearts have a complete septum separating oxygenated and deoxygenated blood.
Explanation: The fish circulatory system is simpler and less efficient than mammals’. The single circulation means blood pressure drops after passing through gills, while mammals maintain high pressure to body tissues due to double circulation. The four-chambered heart in mammals completely separates oxygenated and deoxygenated blood, making oxygen delivery more efficient.
(b)
1. Prevents mixing of oxygenated and deoxygenated blood, maintaining high oxygen delivery efficiency.
2. Allows blood to flow at high pressure to body tissues, enabling rapid nutrient and oxygen delivery.
3. Enables efficient waste removal (carbon dioxide, urea) from tissues.
4. Maintains lower pressure in pulmonary circuit to protect delicate lung capillaries.
5. Supports higher metabolic rates needed for endothermy (warm-bloodedness) in mammals.
Explanation: The double circulatory system separates systemic and pulmonary circuits, allowing different pressure optimizations. The high pressure systemic circuit delivers oxygen effectively to all tissues, while the lower pressure pulmonary circuit prevents lung damage. This separation is crucial for maintaining the high metabolic demands of mammals.
(c)(i)
Absorption of digestion products: C (small intestine)
Excretion of CO₂: A (lungs)
Formation of urine: D (kidneys)
Production of bile: B (liver)
Explanation: The small intestine (C) absorbs digested nutrients into blood capillaries. Lungs (A) excrete carbon dioxide during gas exchange. Kidneys (D) filter blood to form urine. The liver (B) produces bile which aids fat digestion.
(c)(ii) Hepatic portal vein
Explanation: The hepatic portal vein carries nutrient-rich blood from the digestive organs to the liver for processing before this blood enters general circulation.
(d)
1. Deaminates excess amino acids, removing toxic amino groups which are converted to urea.
2. Converts ammonia (toxic) into urea (less toxic) which is excreted by kidneys.
3. Breaks down old red blood cells, processing hemoglobin into bile pigments.
4. Detoxifies harmful substances like alcohol and drugs by chemical modification.
5. Processes lactic acid produced during anaerobic respiration.
Explanation: The liver acts as the body’s main chemical processing plant for excretion. By converting toxic substances like ammonia into less harmful ones like urea, and breaking down various waste products, it plays a crucial role in maintaining the body’s internal environment. The urea produced is then filtered out by the kidneys.
(a) Fig. 1.1 is a photograph of a fish. Fig. 1.2 is a photograph of an amphibian.
State two visible features that distinguish the fish in Fig. 1.1 from the amphibian in Fig. 1.2.
(b) Fish, amphibians and mammals are all vertebrate groups. State the name of one other vertebrate group.
(c) Fig. 1.3 shows the circulatory system of a fish. Fig. 1.4 shows the circulatory system of an amphibian.
Describe the similarities and the differences between the circulatory systems of the fish and the amphibian in Fig. 1.3 and Fig. 1.4.
(d) Explain the advantages of the type of circulatory system in mammals compared with the type of circulatory system in fish.
(e) Explain how the structure of arteries and veins relates to the difference in the pressure of the blood transported by these vessels.
(f) Table 1.1 shows the names of some organs and the name of the main artery that brings blood to the organ. Complete Table 1.1.
▶️ Answer/Explanation
Ans:
(a) Fish have fins/scales, while amphibians have limbs/moist skin. These are distinguishing features visible in the images.
(b) Other vertebrate groups include reptiles and birds, which are also part of the five main vertebrate classes.
(c) Both fish and amphibians have a heart with valves, but fish have a 2-chambered heart and a single circulatory system, while amphibians have a 3-chambered heart and an incomplete double circulatory system.
(d) Mammals have a double circulatory system, which maintains higher blood pressure for efficient oxygen delivery, unlike fish where blood pressure drops after passing through gills.
(e) Arteries have thick, muscular walls to withstand high pressure, while veins have thinner walls and valves to prevent backflow due to low pressure.
(f) 