All living organisms need certain things to survive, including water, food, gas exchange, and waste disposal. In humans and other multicellular organisms, cells get what they need through the circulatory system. The circulatory system delivers oxygen, water, and nutrients to cells through blood vessels and removes carbon dioxide waste. The heart pumps blood through a closed loop system of arteries, capillaries, and veins, with capillaries next to cells for exchange. Blood picks up oxygen in the lungs and drops off carbon dioxide as it circulates continuously through this pathway, providing cells with what they require to survive.

1. Living Systems Focus Question: What do living organisms need to survive? Lesson 1-1A

12. Ideas