All cells are able take in bits from their environment and digest them for energy. A long time ago, all organisms were single-celled. This means that they were only made of one cell. They could get all their energy from the ocean and the sun.

Swallowing cells have the ability to eat other smaller cells.

Later, some big cells figured out how to swallow other smaller cells. These were swallowing cells. These cells were able to get energy a lot faster! These swallowing cells helped create more complex digestion and immune systems.

Cooperation & Specialization

Millions of years ago, cells started to be able to work together. They cooperated! This means they didn't have to do everything themselves - they had help! Some cells on the outside of the animal became skin. Some swallowing cells became really good at absorbing food and were in charge of eating and getting energy.

Cell have to talk to each other to cooperate. Cells don't speak, but they have signals that they send to each other. And, they can touch each other and feel the other cell.

The sponge has a cavity lined with eating cells.

Some swallowing cells became really good at moving around and finding harmful cells or particles, like in the sponge to the right. This was the beginning of a simple immune system!

Bigger animals (like humans) still use special cells to swallow harmful things like bacteria, viruses, or old dead cells. So what was once a way to get food became a form of protection too!

These swallowing cells are found in the immune system of human beings too! They are called macrophages and B cells.

As animals got larger, these mechanisms were not enough Find out what happened next>>

All cells are able to absorb small particles from their environment and digest them for energy. Early on, all organisms were single-celled. These cells could get all their energy from the ocean and the sun. They absorbed and digested what they could, individually.

Swallowing cells have the ability to eat other smaller cells.

Then, some cells appeared that had the ability to swallow other smaller cells - the swallowing cells. These cells were able to get energy a lot faster! These swallowing cells became central to the development of more complex digestion and immune systems.

Cooperation & Specialization

Millions of years ago, cells started to be able to work together. This cooperation allowed the cells that make up these tiny animals to start specializing, and carry out different roles. Some cells on the outside of the animal become tougher to protect the animal like a sort of skin. Some swallowing cells became really good at absorbing food and took over eating. In very small animals, this works very well, as all cells are very close to eating cells, so they can easily share energy with their neighboring cells.

Cell cooperation involves cells being able to communicate with each other. This communication is at the basis of almost all processes in your body! For example, your immune cells use tiny chemicals to work together, and your neurons and muscle cells send electrical signals from one to another.

The sponge has a cavity lined with eating cells.

Some swallowing cells became really good at moving around and sniffing out harmful cells or particles, like in the sponge to the right. This is the beginning of a simple immune system!

Even in modern animals, the ancient ability to swallow up certain cells and small debris has been retained by some special cells. So, in addition to digesting food, swallowing cells can destroy things that may be harmful to an animal, like some kinds of bacteria, viruses, or old dead cells.  So what was once a form of nutrition became a form of protection too!

These swallowing cells are found in the immune system of human beings too! They are called macrophages and B cells.

As animals got larger, these mechanisms were not enough. Find out what happened next>>