<p>Seems like you have two questions here:</p>
<ol>
<li><p>BA vs. BS degree program. It is usually school-specific as to what the difference is, in terms of course requirements.</p></li>
<li><p>Second major in biology. Obviously, this adds significantly more course work. What would be your reason for doing so? Biology is not a particularly high demand major in the job market, as there are huge numbers of graduates every year.</p></li>
</ol>