You can apply for a Biology TAship through the UBC Biology website.
Applications for the upcoming winter session (September - April) usually open in spring of every year and are usually due a month later after the application opens. Zoology students who rely on TAships as part of their funding plan are guaranteed a winter session TA position as long as they apply by the deadline.
There are also TA opportunities in the summer session (May - August) but there are fewer of them and usually with fewer hours TAships in the winter session.
TA rates and classifications can be found on the CUPE 2278 website.