(a) What are hormones?
(b) In a tabular form, state four differences between nervous coordination and hormonal coordination in humans.
(c) State three effects each of: (i) Over-secretion (ii) Under-secretion of thyroxin on mammals.
(d) Make a diagram 10 – 12cm long of the reflex arc and label fully.
Explanation
(a) Hormones – These are chemical substances secreted by endocrine/ductless glands, directly into the blood/ circulatory system, which on reaching a target organ, stimulate activity of that organ.
| Hormonal | Nervous |
| Transmission is chemical | transmission is mechanical and chemical |
| slow transmission | Rapid transmission |
| Response is wide spread | Response localized |
| Target organs receive response | effector organs receive response |
| Long last response | short-lived response |
| pathway not specific through blood | pathway specific through nerves fibres |
(c)(i) Effects of over-secretion: –
- Over active/Hyperactive/Irritable/nervous.
- Excessive growth/gigantism
- Loss of weight
- Enlarged thyroid gland/exothalmic goitre
- Accelerated/increased heartbeat
- Protrusion/bulging out of eyeball.
(ii) Effects of under-secretion: –
- Cretinism/dwarfism in children.
- Overweight/increase in subcutaneous fat/obesity.
- Physical/mental sluggishness in adults.
- Reduced heart rate.
- Lowered/reduced metabolic rate/ myxceodema.
- Goitre formation/hyperplastic goiter.
(d) Labels: Receptor organ, sensory neurone, intermediate/relay neurone; motor neurone, synapse, spinal cord, ventral root, dorsal root, effector organ, spinal nerve.