Bacteria are tiny, single-celled organisms that can be found almost everywhere on Earth, from soil to water and even inside our bodies. They are so small that you need a microscope to see them. While some bacteria can cause diseases, many are actually helpful. For example, certain bacteria in our gut help us digest food and keep our immune system strong. Bacteria come in various shapes, such as spheres, rods, and spirals. They reproduce quickly by dividing, which allows them to adapt to different environments. Scientists study bacteria to understand their roles in ecosystems and to develop medicines, like antibiotics, that can fight harmful bacteria and protect our health.