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Question

Which of the following classes of animals has/have three-chambered heart?

This question was previously asked in
CDS I 2018 Elementary Mathematics Previous Year Paper (04-Feb-2018)
The correct answer is

Amphibia and Reptilia

Understanding Animal Heart Chambers

The heart is a vital organ responsible for pumping blood throughout the body. The number of chambers in the heart varies across different animal classes, reflecting their evolutionary adaptations and physiological needs. These chambers include atria (receiving chambers) and ventricles (pumping chambers).

Heart Chambers in Different Vertebrate Classes

Let's look at the number of heart chambers found in different classes of vertebrates:

  • Pisces (Fishes): Fishes have a two-chambered heart. This heart has one atrium and one ventricle. It pumps deoxygenated blood to the gills for oxygenation.
  • Amphibia (Amphibians like frogs, salamanders): Amphibians typically have a three-chambered heart. This heart consists of two atria and one ventricle. The two atria receive oxygenated blood from the lungs/skin and deoxygenated blood from the body, respectively. Both types of blood mix to some extent in the single ventricle before being pumped out.
  • Reptilia (Reptiles like lizards, snakes, turtles): Most reptiles also have a three-chambered heart, similar to amphibians, with two atria and one ventricle. However, the ventricle in most reptiles has an incomplete septum (wall) that partially separates oxygenated and deoxygenated blood. Crocodiles are an exception among reptiles, possessing a four-chambered heart.
  • Aves (Birds): Birds have a four-chambered heart, with two atria and two ventricles. This allows for complete separation of oxygenated and deoxygenated blood, which is highly efficient for their high metabolic rate.
  • Mammalia (Mammals): Mammals also have a four-chambered heart, just like birds, with two atria and two ventricles. This complete separation of blood is crucial for maintaining a high and constant body temperature.

Analyzing the Options for Three-Chambered Heart

The question asks which classes have a three-chambered heart. Based on our understanding of animal heart chambers:

  • Pisces: Have a two-chambered heart.
  • Amphibia: Have a three-chambered heart.
  • Reptilia: Mostly have a three-chambered heart (with crocodiles being the exception having four).

Let's evaluate the given options:

  • Option 1: Pisces and Amphibia - Pisces have 2 chambers, Amphibia have 3. Incorrect.
  • Option 2: Amphibia and Reptilia - Amphibia have 3 chambers. Reptilia mostly have 3 chambers. This option correctly identifies both classes where a three-chambered heart is characteristic (though with the notable exception in Reptilia).
  • Option 3: Reptilia only - While most reptiles have 3 chambers, amphibians also do. This option is incomplete.
  • Option 4: Amphibia only - While amphibians have 3 chambers, most reptiles also do. This option is incomplete.

Considering the common characteristic, both Amphibia and the majority of Reptilia possess a three-chambered heart structure.

Summary of Heart Chambers by Class

Animal Class Number of Heart Chambers Description
Pisces 2 1 Atrium, 1 Ventricle
Amphibia 3 2 Atria, 1 Ventricle
Reptilia Mostly 3 (Crocodiles 4) 2 Atria, 1 Ventricle (with incomplete septum in most); 2 Atria, 2 Ventricles (Crocodiles)
Aves 4 2 Atria, 2 Ventricles
Mammalia 4 2 Atria, 2 Ventricles

The classes of animals that generally have a three-chambered heart are Amphibia and Reptilia.

Revision Table: Vertebrate Heart Structure

Class Heart Chambers Circulation Type
Pisces 2 Single
Amphibia 3 Incomplete Double
Reptilia (most) 3 Incomplete Double
Reptilia (crocodiles) 4 Complete Double
Aves 4 Complete Double
Mammalia 4 Complete Double

Additional Information: Significance of Heart Chambers

The number of heart chambers is directly related to the efficiency of the circulatory system and the animal's metabolic rate. A two-chambered heart facilitates single circulation (blood passes through the heart once per cycle), suitable for lower metabolic demands. Three-chambered hearts allow for incomplete double circulation, where pulmonary and systemic circuits are somewhat separated, improving oxygen delivery compared to single circulation. Four-chambered hearts facilitate complete double circulation, fully separating oxygenated and deoxygenated blood, which is highly efficient and supports the high metabolic demands of endothermic animals (birds and mammals).

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