K.C.S.E Biology Q & A - MODEL 2006PP2QN06

K.C.S.E Biology Q & A - MODEL 2006PP2QN06

An experiment was carried out to investigate the effect of hormones on growth of lateral buds of three pea plants
The shoots were treated as follows:
Shoot A – Apical bud was removed.
Shoot B – Apical bud was removed and gibberellic acid placed on the cut shoot.
Shoot C – Apical bud was left intact.
The length of the branches developing from lateral buds were determined at regular intervals.
The results obtained are as shown in the table below.

a) Using the same axes, draw graphs to show the lengths of branches against time.
b)i) What was the length of the branch in shoot B on the 7th day? 
ii) What would be the expected length of the branch developing from shoot A on the 11th day? 
c) Account for the results Obtained in the experiment 
d) Why was shoot C included in the Experiment? 
e) What is the importance of gibberellic acid in agriculture? 
f) State two physiological processes that are brought about by the application of gibberellic acid on plants.

answers

(b) (i) 105 + 1 (mm)
     (ii) 134 – 140 (mm)
(c) Graph A: The tip of the shoot  which was removed contained indole acetic acid (IAA); which causes apical dominance/ inhibits growth/ development of more lateral  buds; hence lateral buds sprouted/grew.
Graph B; the gibberellic acid which was added on the cut. Promotes formation of lateral branches of stems, hence the fast growth of branches on shoot b.
Graph C; The shoot tip which remained intact  contains IAA which inhibits growth/ development of lateral buds; hence little change of length of lateral branches.
(d) Control
(e) Increase productivity
(f) Promote cell division, and cell elongation