1. how many chambers does the human heart have? 2. what close the valves in the heart and why should they do this?

3. what do we call a pulse?

4. describe blood capillaries

Your heart has four separate chambers that pump blood, two on the right side and two on the left.

2. When the ventricle relaxes, the aortic valve closes to prevent blood from flowing back into the ventricle. When the aortic valve is not working properly, it can interfere with blood flow and cause the heart to strain to send blood to the rest of the body.

3. In medicine, a person's pulse is a pressure wave caused by the expansion of the arteries as a result of the circulation of blood pumped by the heart.

4. Capillaries are tiny vessels that branch out from arterioles to form networks around body cells.

Capillaries are very tiny blood vessels — so small that a single red blood cell can barely fit through them.

hope this help! ^^

for the points

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.