Rocket draws a giant ladder on the lab board. "Each step is a body level!" he says.
He writes "organ" on the bottom step. Then he frowns. "Wait. That is not the start."
Raven grins. "Good catch! What do you notice about the smallest level?"
Nova taps the bottom rung. "Start with the tiniest builder," she says. "Then climb."
Each level is built from the level below it.
Cells make tissues. Tissues make organs. Organs make systems.
All the systems together make one whole body: you!
| Level | Example | Made of |
|---|---|---|
| cell | a nerve cell | a membrane, a nucleus and cytoplasm |
| tissue | muscle tissue | many similar cells |
| organ | the stomach | several kinds of tissue |
| system | the digestive system | several organs |
Scientists say a cell's shape and its job are closely linked.
A very thin cell would not be good at protecting.
Muscle cells are long and thin, so they can shorten and pull.
The heart wall is made of muscle, so it can squeeze and pump.
| Week check | True or false? |
|---|---|
| The nucleus is the control center of a cell. | ? |
| A tissue is made of different organs. | ? |
| The stomach is an organ. | ? |
| The lungs and windpipe are part of the respiratory system. | ? |
You climbed the whole ladder! Tomorrow is Body Lab Day. Your family builds a body systems map.