Question

Which circulatory system description best matches the group(s) of animals? a. Cephalopod mollusks such as squids and octopuses have open circulatory systems with ventricles that pump blood away from the heart. b. Fishes have a single-chambered heart with an atrium that pumps blood through gills for oxygen exchange. c. Amphibians have the most oxygenated blood in the pulmocutaneous circuit and the most deoxygenated blood in the systemic circuit. d. Amphibians and reptiles use a two-chambered heart to separate oxygenated and deoxygenated blood. e. Birds and mammals pump blood to separate pulmonary and systemic systems from two separate ventricles in a four-chambered heart.

Short answer

Option e is correct; birds and mammals have a four-chambered heart that pumps blood to separate pulmonary and systemic circuits from two separate ventricles.

Step-by-step solution

- Analyzing open circulatory systems

Evaluate option a. Cephalopods have a closed circulatory system, not an open one. The description provided is incorrect because cephalopods have a more complex system with multiple hearts and closed circulation.

- Investigating fish circulatory systems

Look at option b. Fishes do have a two-chambered heart but it's not described as single-chambered. The heart consists of one atrium and one ventricle, and the atrium doesn't pump blood through the gills; it collects blood that returns from the body and passes it to the ventricle.

- Examining amphibian circulation

Check the facts in option c. Amphibians do indeed have a three-chambered heart, with a pulmocutaneous circuit that sends blood to the lungs and skin for oxygenation. The systemic circuit sends blood to the rest of the body. The description is thus partially correct, but does not mention that amphibians have a three-chambered heart.

- Assessing amphibian and reptile heart chambers

Option d states that amphibians and reptiles use a two-chambered heart. This is incorrect as amphibians have a three-chambered heart with two atria and one ventricle, while reptiles (except for crocodilians) have a three-chambered heart with a partial septum in the ventricle, which helps separate oxygenated and deoxygenated blood.

- Considering the avian and mammalian heart structure

Analyze option e. Birds and mammals indeed have a four-chambered heart with separate pulmonary (lungs) and systemic (body) circuits, allowing for efficient separation of oxygenated and deoxygenated blood. This description is accurate.

Key concepts

Cephalopod Closed Circulatory System

Cephalopods, such as squids and octopuses, possess a sophisticated closed circulatory system that contrasts with open circulatory systems found in other mollusks. A closed system means that the blood remains within a continuous network of vessels, allowing for better control of blood distribution and higher pressures to transport nutrients, gases, and waste efficiently.

In cephalopods, multiple hearts work in conjunction, with a main systemic heart pumping oxygenated blood to the body, whilst additional branchial hearts are dedicated to pumping blood through the gills for oxygenation. This system enables cephalopods to be highly active and responsive to their environment.

Fish Two-Chambered Heart

Fish are equipped with a simple yet effective two-chambered heart, consisting of one atrium and one ventricle. The atrium receives deoxygenated blood from the body and then transfers it to the ventricle. The ventricle pumps this blood to the gills where gas exchange occurs; oxygen is absorbed and carbon dioxide is expelled.

This circulatory system is termed 'single-loop' because the blood passes through the heart only once during each complete cycle through the body. While this system is efficient for aquatic life where blood pressure can be lower, it limits the capacity to supply highly oxygenated blood under greater demand, as seen in more active or larger terrestrial vertebrates.

Amphibian Three-Chambered Heart

Amphibians, creatures that live both in water and on land, have a three-chambered heart, an adaptation reflecting their dual life stages. This heart comprises two atria and one ventricle. One atrium receives deoxygenated blood from the body, and the other receives oxygenated blood from the pulmocutaneous circuit which involves the lungs and skin.

While this configuration allows some mixing of oxygenated and deoxygenated blood in the single ventricle, the mixing is minimized by the timing of the heart contractions and the way the blood is channeled, which maintains relatively efficient oxygen distribution. Amphibians' ability to breathe through their skin in addition to their lungs makes this system suitable for their varied habitats and activities.

Reptilian Cardiac Structure

Most reptiles, except for crocodilians, have a heart with three chambers: two atria and a ventricle that is partially divided by a septum. This partial division helps to reduce the mixing of oxygen-rich and oxygen-poor blood within the ventricle, a feature that is vital for ectothermic (cold-blooded) creatures who rely on external sources of heat to regulate their body temperature.

Although not as efficient as the four-chambered hearts of birds and mammals, this structure allows for variation in oxygen delivery that can be moderated according to the reptile's metabolic needs. This is particularly useful during periods of inactivity or when basking in the sun, as it enables a level of control over energy consumption.

Avian and Mammalian Four-Chambered Heart

Birds and mammals have evolved a highly advanced four-chambered heart, which fully separates oxygenated and deoxygenated blood. It features two atria and two ventricles, with the right side of the heart handling deoxygenated blood that flows to the lungs, while the left side pumps oxygenated blood to the body.

This complete separation is crucial for endothermic (warm-blooded) organisms, as it ensures a consistent and efficient supply of oxygen to maintain high metabolic rates necessary for activities such as flight in birds or sustained endurance in mammals. Moreover, the four-chambered design prevents any mixing of blood, maximizing oxygen delivery and energy production in cells throughout the body.