Life Sciences Paper 1, November 2024, question 3.5.4

A learner investigated how auxins affect the growth of shoots. Twelve seedlings of the same species were split into three sets (P, Q and R) of four seedlings each. All seedlings were kept in darkness for 72 hours. - Set P: the shoot tips were left on and not treated. - Set Q: the shoot tips were cut off. A small block of agar jelly containing auxins was placed on the cut surface, but only on the right-hand side of the stump (agar lets substances diffuse through it). - Set R: the shoot tips were cut off and a block of agar jelly without auxins was placed centrally on the cut surface. The diagram below shows how the shoot tips of the three sets were treated.