BTo carry blood away from the heart at high pressure
CTo exchange oxygen, nutrients, and waste between blood and cells
DTo carry blood back to the heart
Capillaries are the smallest blood vessels, with walls just one cell thick. This thinness allows oxygen and nutrients to pass from the blood into surrounding cells, and waste products like carbon dioxide to pass from cells into the blood. Arteries carry blood away from the heart, veins return it, and the heart pumps it — but the actual exchange happens in the capillaries.
Question 2 True / False
Deoxygenated blood in your veins is blue.
TTrue
FFalse
Answer: False
Blood is never blue inside the body. Oxygenated blood is bright red, and deoxygenated blood is dark red. Textbook diagrams use blue for deoxygenated blood only as a visual convention to make the two types easy to distinguish. Veins may appear blue through your skin because of how light penetrates skin and reflects back.
Question 3 Short Answer
Describe the path blood takes from the heart to the lungs and back, and explain why this trip is necessary.
Think about your answer, then reveal below.
Model answer: The right side of the heart pumps deoxygenated blood to the lungs, where it picks up oxygen and releases carbon dioxide. The oxygen-rich blood then returns to the left side of the heart, which pumps it out to the rest of the body. This trip is necessary because blood must be resupplied with oxygen to deliver it to cells.
This describes pulmonary circulation — the loop between the heart and lungs. It connects the circulatory and respiratory systems: the lungs reload the blood with oxygen, and the heart pumps it to the body. Without this loop, cells would run out of oxygen.