Question

If there is a complete mixing of an oxygenated and deoxygenated blood in the heart then
a) Blood to the lungs would be low in oxygen and the tissues would receive blood rich in oxygen
b) Blood to the lungs would be rich in oxygen and the tissues would receive blood low in oxygen
c) lungs and tissues would receive blood with the same amounts of oxygen
d) Tissues would receive completely oxygenated blood and lungs would receive deoxygenated blood.

Answer 1

Hint: The complete mixing of blood is normally seen when the chambers of the heart are not completely formed. Mammals also show mixing of blood in case there is a heart defect.

Complete answer:
This question can be approached in two ways
A) Mixing of blood is normal in Amphibians as they show three-chambered hearts. The heart consists of two auricles and one ventricle. The left and right auricles collect the blood from the lungs and the body respectively and the blood then enters the ventricle. Due to the presence of only one ventricle, the blood from the auricles mixes and thus mixed blood from the ventricles flow in the body and the lungs too. thus the lungs and the tissues receive blood with the same amounts of oxygen (this is mixed blood).

B) In mammals, there are two auricles and two ventricles. Thus the oxygenated and deoxygenated blood never mixes. Thus the blood that enters the tissues and the lungs vary in the amount of oxygen. However Ventricular septal defect shows the mixing of blood. This defect is a hole between the left and right ventricle and thus mixing of blood is seen. Thus the blood entering the tissues and the lungs will have the same amount of oxygen.

Thus the answer will be option C whether approached by either of the ways.

The fourth option explains the type of blood circulation seen in mammals and birds and this is known as Double Circulation. The heart receives both oxygenated and deoxygenated blood. The heart pumps the deoxygenated blood to the lungs so that it gets purified and then returns to the heart so that it is pumped into the tissues. Thus the blood comes in contact with the heart twice and this is Double Circulation.

Note: Vertebrates show great evolution in the chambers of the heart. Pisces have two chambers, Amphibians and Reptiles (except crocodile) have three chambers while mammals and aves have four chambers. This increase in chambers is responsible for the circulation of pure or oxygenated blood in the body. This is important because the life processes greatly depend on the oxygen present in the blood.