Hello, teaching is a vey good profession. And if you have decided to choose teaching as your career than plan accordingly. Right after completing your 12th, opt for a bachelor's degree in botany. After completing bachelor's, you can go for B.ED which is bachelor's in elemenatry education. Those who have b.ed degree are usually given more preference. If you wish you can go for Post graduate in botany after bachelors, as it will increase your qualification level and knowledge. Appear for entrance exams like CTET.  

Hello dear 
You want to teach botany to higher secondary students , for that you will have to become pgt means post graduate teacher .
Firstly you will have to clear your graduation in botany with atleast 50% marks and then post graduation in botany with atleast 50 % marks and then you become eligible for becoming pgt and can apply for it in schools or give exams if you want to be a pgt in government schools .
One important thing is that you don't need to appear for ctet exam , as ctet is compulsory for becoming tgt(trained graduate teacher).
Thankyou 
Please feel free to ask your further queries if any.