<span>
a. phosphate. </span>The polar head of a phospholipid is negatively charged and is made up of phosphate molecules. This polar head region attracts water (hydrophilic) and is positioned outward to interact with water.
Blood flows through your heart and lungs in four steps: The right atrium receives oxygen-poor blood from the body and pumps it to the right ventricle through the tricuspid valve. The right ventricle pumps the oxygen-poor blood to the lungs through the pulmonary valve.