Deoxygenated blood first enters in _________ part in fishes?

Correct answer: A. Sinus venosus

  • A. Sinus venosus
  • B. Right atrium
  • C. Left atrium
  • D. Conus arteriosus

Explanation

In fish, blood returning from body tissues first enters the sinus venosus, which passes it to the atrium and then the ventricle. Fish have a single atrium rather than separate right and left atria, so students may incorrectly select right atrium by applying the mammalian heart plan.

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