Which two factors below make rapid and substantial blood loss life-threatening?
a. loss of immunity and loss of blood pressure
b. loss of immunity and loss of carbon dioxide carrying capacity
c. loss of clotting ability and loss of osmotic pressure
d. loss of blood pressure and loss of oxygen-carrying capacity

The correct answer is: d. loss of blood pressure and loss of oxygen-carrying capacity.

Explanation:

Blood is a liquid connective tissue which is the major component responsible for transporting nutrients and oxygen to all the cells in the body and for removing carbon dioxide and metabolic wastes from all the cells of the body.When there is excessive blood loss, the total volume of blood in the body decreases far below normal. As a result of this the blood pressure (pressure applied by the blood on the walls of the arteries) decreases.This is because the rate at which blood is lost is far more than the rate at which it is produced.The decrease in blood pressure prevents the blood from travelling easily against the gravity, hence it is unable to reach all the regions of the body, thereby depriving many cells of nutrients and oxygen. The waste products are also not efficiently collected from these cells. This causes the cells in the deprived regions to die.Blood carries the most important component required for respiration and metabolism, that is oxygen, in association with haemoglobin molecules. Excessive blood loss causes loss of haemoglobin as well. This can cause reduction in the oxygen-carrying capacity of blood. Hence the cells of the body are unable to carry out metabolic activities properly due to the dearth of oxygen. This causes the death of cells.Excessive death of cells causes tissues to become non-functional and that can cause organ failure. Multiple organ failure can pose severe threat to life.