Which substance is constantly processed by some excretory organs even though it is not excreted by the excretory system?

The correct answer is-

Blood.

Excretion is mechanism of removal of waste material and excess of water from the body. Organs of excretion (such as kidney, skin, large intestine, lungs, and liver) form the excretory system.

The kidneys (part of urinary system) are considered as the main excretory organ in human that perform continuous filteration of blood to remove nitrogenous waste, excess of water and salts out of body. It forms urine that is excreted out of the body.

Therefore, blood is constantly processed by some excretory organs and the waste products are excreted out of the body without the excretion of blood.

atp is used for energy.