Bacteria are tiny organisms, which we are not able to see unless we use special equipment. Bacteria are unicellular, meaning they are made of only one cell. In contrast, we are multicellular, made of many cells. Bacteria reproduce by making more copies of themselves. These organisms are found everywhere around us, even on and within our bodies! Bacteria hang out on all surfaces inside: such as desks, computer keyboards, doorknobs, and floors, and outside: such as trees, plants, soil, and lakes. They are on our skin, and inside our body, mainly in our noses, mouths and guts. Some extra-tough bacteria make their homes in extreme places like hot springs, the bottom of the ocean, and even outer space! Scientists think there may be between millions and trillions of species of bacteria on Earth.

Bacteria are diverse; different species have variety of traits. Some species are harmful and make us sick, many are neutral or helpful. The bad species may give someone food poisoning, pneumonia, or skin infections, to name a few. Some good species help create foods such as yogurt, cheese or bread. Some can help plants get nutrients(energy) from the soil! Good bacteria can aid us with our bodily processes, especially digesting our food.

You can learn a lot about bacteria by growing them on a petri dish, and looking at them under a microscope. A clump of bacteria you can see on the petri dish is called a colony. That means the bacteria made enough copies of themselves, for us to see the group. Colonies may be different shapes, and sizes. They may appear beige, orange, red, or other colors. A microscope will help you get an up-close view of the cells! Cells may be shaped like ovals, circles or spirals. They may be lined up in chains or pairs, or gathered in clumps. You can do tests on the bacteria to look at what they're made of, or their metabolism (processes within the cell that keep them alive). Some types of bacteria can move, others cannot.