If these minor changes help an organism to grow better than its competitors, that organism may outgrow his neighbors. Mutations are constantly occurring. Nearly all mutations are harmful, meaning the change is not quite as good as the original, but some mutations give an organism an advantage over his neighbors. Genetics is the science of studying genetic material. Bacteria are good subjects for studying the basic laws of inheritance because they grow rapidly and and have traits which are easily studied.
Bacteria are important in food preparation and preservation.
Firstly, many species would love to eat our food and we must find a way to keep them out or slow their growth. For example, foods retain their value longer when frozen because few bacteria can grow in a freezer, and the low temperature also slows biochemical reactions. Secondly, certain bacteria have specialized metabolisms which are ideal for food fermentations. For example, man has found many species which can digest sugars but not proteins. These species are very useful in food preparation if they produce acids which slow the growth of other organisms which would eat the proteins.