(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.
Explanation
(a)(1) Voluntary action - involves the response to a stimulus that is controlled at will by the brain. in this action, an impulse is carried from a sensory neurone via the spinal cord to the brain which interprets and sends the message back through the motor neurone to effector organ. The action is not automatic. e.g. running, writing, jumping, laughing, reading, smiling.
(II) Involuntary action or reflex action-It is a rapid or automatic response to a stimulus. It does not involve the brain for initiation. Therefore, the action is not under the control of the will, e.g. sneezing, coughing, knee jerk, salivation, secretion of grand, blinking
(b)(i) Functions of insulin:
(1) Assists in oxidation of glucose to produce energy
(2) regulates the amount or level of glucose in the blood
(3) assists in protein synthesis in some cells
(ii) Functions of auxin
(1) Promotes lateral bud development
(2) promotes reproduction, flowering and fruit formation in plants
(3) promotes the production of adventitious roots.
(c) Experiment to show that plant roots respond positively to gravity:
Aim - To demonstrate that plant roots respond positively to gravity.
Apparatus: A bean seedling, Wet blotting paper, damp saw dust, cupboard.
Procedure: Put some dust on a wet blotting paper and place the bean seedling on the saw dust horizontally. Carry the set up and place it inside a dark cupboard to eliminate light for few days.
Observation: When observed after few days, one will discover that the root has curved and growing downwards while the shoot grow upward. Conclusion: Since the root has grown downwards and the shoot upwards, we can say that roots respond to gravity, showing positive geotropism while the shoot shows negative geotropism.