The circulatory system
Blood flows through blood vessels. It carries oxygen and nutrients to the cells and takes away waste and carbon dioxide. Blood has a liquid part and cells: red blood cells carry oxygen and make blood red; white blood cells defend against germs and viruses; platelets stop bleeding. The heart is a muscular pump that never stops pushing blood; it is about the size of your fist. Blood goes from the heart to the lungs to pick up oxygen, returns to the heart, and the heart pumps it around the body. Immunity is the body’s ability to resist disease; white cells “remember” germs. To strengthen immunity: daily exercise, good food, enough sleep, walks in fresh air, a routine, dressing for the weather and gradual hardening (with adults, never plunging suddenly into cold water).
Pulse measuring: find the pulse at your wrist with two fingers, count beats for 15 seconds and multiply by 4 (beats per minute). Then do 20 jumps and measure again. What changed? Record it.