Multi-cell organisms

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Heartbeat RestingRunning

Most living things you can see are made of many cells. You have trillions!
Cells of the same kind team up into a tissue.
Different tissues team up into an organ, like the heart, the brain, or a leaf.
Organs team up into an organ system, like the circulatory system or the shoot system.
All the systems together make an organism: one whole living thing.