Does not taking Vector calc in undergrad (US) affect my chances for grad school application So I'm a current junior Biochem major thinking of doing a phd in a bioscience/life science field (something related to virology/immunology/biochem). One of my final math requirements is either Vector Calculus (Calc 3), Intro to ordinary differential equations, and a math course tailored to biochem/chem majors called Mathematical Physics for chem/biochem majors.

Would (US) grad schools care as to which of these 3 classes I took (vector calc is worth more credits and is accepted to be harder/more time consuming)?
I don't feel I will have time during my semester to take Vector Calc.
In the US, at least, the boundary between admission and refusal for graduate school is nowhere near that narrow. Your program will be looked at overall for indicators of success in the program you are entering. If you can show that nearly everything in your application materials is evidence of future success then the details (within reason) matter less. 

Moreover, most beginning grad students in the US, take coursework as well as start to think about research. Your advisor might (strongly) recommend, at that point, that you take some course(s). 

But some courses will help more than others to indicate your success, though it is probably more important that you do well in which ever course you take.