(a) What are hormones? (b) In a tabular form, state four differences between nervous coordination and hormonal coordination in humans. (c) State three effec...
Question 1 Report
(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.
Answer Details
(a) Hormones
Hormones are chemical substances (organic compounds) produced in very small quantities by the endocrine (ductless) glands of the body, and carried by the bloodstream to specific target organs where they regulate and coordinate the body's activities, growth and development.
(b) Four differences between nervous and hormonal coordination
| Nervous coordination | Hormonal coordination |
|---|---|
| Messages travel as electrical impulses along nerves | Messages travel as chemical substances (hormones) in the blood |
| Transmission is very fast | Transmission is comparatively slow |
| The response is usually short-lived (temporary) | The response is usually long-lasting |
| The effect is localised, acting on a specific part | The effect may be widespread, acting on many parts |
(c)(i) Three effects of over-secretion of thyroxin
- Raised metabolic rate leading to loss of body weight despite increased appetite.
- Rapid or irregular heartbeat, restlessness, nervousness and excitability.
- Protrusion of the eyeballs and enlargement of the thyroid gland (exophthalmic goitre / Grave's disease).
(c)(ii) Three effects of under-secretion of thyroxin
- Lowered metabolic rate leading to gain in body weight and sluggishness.
- In children, retarded physical and mental growth (cretinism).
- In adults, swelling of the tissues, dry skin and mental dullness (myxoedema); enlargement of the thyroid (simple goitre) where iodine is lacking.
(d) Diagram of the reflex arc
A labelled diagram, 10 - 12 cm long, should show a spinal-cord reflex arc with these labelled parts arranged in order: receptor in the skin, sensory (afferent) neurone with its cell body in the dorsal root ganglion, dorsal root, the grey matter and white matter of the spinal cord with a relay (intermediate) neurone, synapses, motor (efferent) neurone leaving by the ventral root, and the effector (muscle). Arrows should show the direction of the impulse from receptor to effector.
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