Anaerobic Bacteria
Anaerobic bacteria are tiny living things that grow and thrive without any air or oxygen.
Think of it this way
Sealed jars of pickles sit at the back of a dark pantry shelf. Inside each jar, no air can reach the tiny living things at work. They break down the cucumbers and make the pickles sour. They do it all without a single breath of air.
Explaining anaerobic bacteria by grade level
Some germs do not need air to live. They hide deep in soil where no air can reach. When a carrot sits in wet dirt, these germs help break it down. The carrot gets soft and rots from the inside.