K.C.S.E Biology Q & A - MODEL 2019PP2QN03
In an experiment, students treated seedlings as illustrated below.
(i) Account for the observations made in seedling I.
(ii) Explain the similarity in the end results made in seedlings II and III.
(iii) State the likely treatment that would make seedlings II and III respond like seedling I.
(i) Positive phototropism/tip bends towards light; light causes migration of auxins (produced at the tip) to the darker sides; (of the shoot) resulting in faster division of cells/ elongation/growth on the darker /opposite side of the shoot hence bending towards light
(ii) both seedlings remain upright; ( erect) seedling II does not have tip while seedling III the tip has been covered by opaque material preventing light causing unequal distribution of auxins; . uniform/even distribution of auxins)
(iii) Fitting a gar block treated with auxins at the decapitated end of seedling II; Removing the opaque material covering the tip of seedling III/ replacing the opaque cap with a transparent one;