Theory question 104
Hormonal Coordination(a) Explain the following terms (i) voluntary action (ii) involuntary action
(b) State three functions each of (i) insulin (ii) auxins.
(c) Describe an experiment to show that plant roots respond positively to gravity.
Show the model answer
(a)(i) Voluntary action: an action done consciously, by will, controlled by the cerebrum, e.g. writing, walking
(ii) Involuntary action: an automatic action not under conscious control, e.g. heartbeat, breathing, reflexes like blinking
(b)(i) Insulin: lowers blood sugar; makes the liver and muscles change glucose to glycogen; increases uptake of glucose by cells; increases oxidation of glucose; promotes conversion of glucose to fat
(ii) Auxins: cause cell elongation/growth; control tropisms; promote root formation in cuttings; cause fruit development without fertilisation; prevent leaf and fruit fall; apical dominance
(c) Pin germinating seedlings (e.g. bean) with straight radicles horizontally on moist cotton wool/cork in a gas jar or on a klinostat; keep one klinostat still (experiment) and one rotating (control); keep in the dark for 2–3 days
Result: radicles on the still one curve downwards; radicles on the rotating klinostat grow straight
Conclusion: roots are positively geotropic
Give an example with each definition in (a).