The three major subjects under science are Physics, Chemistry and Biology. There is a lot of mathematics involved in Physics, some in Chemistry and not much in Biology.
If you choose to study Biology as your major subject in 11th, you will still need to pass Physics and Chemistry.
The problem with choosing biology is, there are not a lot of career options with biology as your major subject. The competitive exams are tough and you will need to perform well in all three Physics, Chemistry and Biology to crack those exams.
You cannot avoid mathematics altogether since it is involved in almost all the subjects. Unless you choose a creative field like arts, music etc.
If you really like science and want to study it further, I would suggest to push yourself and learn enough mathematics to perform well in Physics and Chemistry.
Edit: Some comments based on Particia's concerns
My answer was keeping in mind an Indian education scenario, since the person who asked the question is studying in India. Allow me to elaborate.
Yes, Math is required in every field. I may have generalised a little when I said not much math is required in Biology or Arts. If a student choses to study Physics in 11th standard, he will be studying Laws of Motion, Work Energy Power, Gravity, Rotational Motion, Thermodynamics, Waves etc. A student has to be good in Algebra, Geometry, Calculus etc to understand these concepts effectively. Compare that to Math requirements in Biology and Arts, I could safely say that Math requirements are not that stringent.
Since he has already studied Math till class 10th, He is familiar with Algebra, Number Systems, Geometry, Trigonometry, Statistics, Mensuration and Probability, I'd say he has enough Math education for requirements in fields like Biology or various under Fine Arts, and Life in general.
I agree I shouldn't have said Math is not required in Fine Arts, I take that back. The comment was very specific to the question and knowing he has passed exams till 9th standard and familiar with concepts taught in 10th standard.
As far as my Biology comment, that was again keeping in mind the career options available in India. Although India is developing fast and new career options are emerging as we speak. There are not many career options available for study with Biology as your choice of subject when compared to Math/ Commerce.