Plants, insects, bacteria, fungi and other organisms are a natural part of the environment. Some can benefit people, while others can be pests that you may need or want to control. You can choose from many different methods to control a pest. One method is to use a pesticide.
Gynecologists, medical doctors specializing in the reproductive health of women, must complete at least 12 years of school and training after high school.
It takes (on average) 4 years of undergrad, 4 years of medical school, and 4 years of residency to become a fully practicing OB/GYN, and up to another 3 years to become a specialist. So at least 12 years. You will have to take biology, microbiology, chemistry, organic chemistry, biochemistry, etc. to become an OB/GYN.