Why do animals (including you) need oxygen? a. It binds with low energy electrons and protons to make water b. It carries energy in the electron transport chain. c. It binds with carbon to make carbon dioxide. d. Red blood cells need oxygen to deliver other nutrients to cells.

Option-A

Explanation:

With the evolution of oxygen on Earth, the anaerobic organisms evolved themselves to use oxygen but still, 75% of the anaerobic organism died at the time when oxygen evolved.

The oxygen was used as the electron acceptor in the last phase of the electron transport taking place in the mitochondria. The oxygen binds with the low energy electron at the end of the chain reaction and with the protons and forms the water molecule. This water is known as the metabolic water.

Thus, Option-A is the correct answer.

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.

a = executive branch; b = judicial branch