AP Bio 9pm, Sky Comedy Whitlock High School’s reluctant biology teacher Jack Carson Griffin (It’s Always Sunny’s Glenn Howerton) returns for a third season of this gentle comedy on the goings-on of the world of public schooling in small-town America. We open with Jack plotting revenge, with the help of his willing students, on the manufacturers of a disappointing popcorn maker he has ordered, while principal’s secretary Helen (Paula Pell) goes back to education to get her high school diploma, sparking chaos in her boss Principal Durbin’s (Patton Oswalt) office. Ammar Kalia 5pm Channel 4 It’s Cake Week for our amateur kid bakers, and in their first technical challenge the group have to undertake an intricate construction that will reveal a pattern when cut into, as well as putting together a cupcake showstopper themed for someone they love. Judges Liam Charles and Ravneet Gill taste the results.