Human heart is made up of how many chambers?

1. A

   Only four

   Option (a) asserts that the human heart consists of only four chambers, which is anatomically correct. These four chambers comprise two upper atria and two lower ventricles that separate oxygenated and deoxygenated blood. This precise structural division makes option (a) the correct and key choice.

2. B

   Only one

   Option (b) claims that the human heart has only one chamber, which is biologically inaccurate. Such a simple structure is found in much simpler organisms, not in mammals like humans. Therefore, option (b) is definitely incorrect.

3. C

   Only three

   Option (c) states that the human heart has only three chambers, a configuration typical of amphibians and most reptiles rather than humans. Humans possess a fully partitioned four-chambered heart to support high metabolic demands. Thus, option (c) is incorrect.

4. D

   Only two

   Option (d) suggests that the human heart has only two chambers, which is characteristic of fish. Since human physiology requires a double circulatory system, this two-chambered claim is wrong.

Summary. Official key is (a) Only four. The human heart is a sophisticated muscular organ divided into four distinct chambers: two atria and two ventricles. This four-chambered design ensures complete separation of oxygenated and deoxygenated blood, optimizing efficiency for warm-blooded mammals. Options claiming one, two, or three chambers describe simpler vertebrate circulatory systems. Consequently, only option (a) correctly identifies the mammalian heart structure.