Cells, Tissues and Organs
All living things are made of cells. Plants, birds, and bacteria are all made of cells.
1 Cell or Many Millions - The Complexity of Life
Cells have existed for millions of years. A cell is the basic unit of Life, which means that all living things are made of cells. Some life forms, like bacteria, are only one cell and others, like humans, are made of millions of cells. Single-cell organisms like bacteria are very efficient organisms, some bacteria live in extreme environments where no human could go without special equipment. In more complex organisms, different groups of cells work together to do different functions particularly well like protecting the body from the outside environment or having muscles and legs to allow the organism to be able to move and look for food instead of just waiting for food to come to them. With increased complexity, comes an increased need for energy and an increased capacity to interact with the world around!..
Cells can work together!
Millions of years ago, life consisted mostly of one-celled organisms, but over time a myriad of bigger and more complex organisms emerged. One of the most interesting things scientists have found was that at some point some cells developed the ability to swallow other cells! Some scientists think this was the beginning of eukaryotic cells.
At some point, some cells started to stick together like glue, forming multicellular organisms (organisms with more than one cell). When cells started to work together, cells were able to start focusing on different things:
- some swallowing cells took over the process of eating for their neighbors, so their neighbors could have time and energy to do other things
- some cells on the outside of the group became really though like the skin on a sponge, to protect their neighbors like the eating cells
- some cells became really good at moving around in a group of cells and sniffing out bad or dead cells to remove them before they harmed their neighbors
This kind of cell cooperation happens all over!
- In your immune system, you have special cells called B and T cells that travel through the body and talk to each other to determine whether a newfound particle is good or bad.
- Your neurons send signals from one to another, and so get messages from your brain all the way to your toes and any other part of the body!
Cells and Tissues
In complex organisms like the human being, you can find many kinds of cells: hair cells, bone cells, stomach cells, immune cells, etc, etc! Each kind of cell works together to form a specific tissue, for example there are a few different kinds of skin cells that work together to form the skin. A tissue is made then of one or more types of cells, something called the extracellular matrix which is sort of the glue that holds all the cells together and also blood vessels, that bring oxygen and nutrients to the cells of each tissue.