Is required to start a chemical reaction

Activation energy

Explanation:

For many reactions, a certain amount of energy must be provided for them to begin. Catalysts introduced to a reaction can help the substances involved reach their activation energies.

answer; both surfaces of the membrane are nonpermeable

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.