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Biology Paper 2,May/June 2008.  
Questions: 1 2 3 4 5 6 7 8 Main
General Comments

Question 7

(a)       What are hormones?                                                                          [3 marks]
 (b)       In a tabular form, state four differences between nervous coordination and hormonal coordination in humans.                                                                                                           [4 marks]

(c)       State three effects each of:
           (i)         Over-secretion;
           (ii)        Under-secretion of thyroxin on mammals.                           [6 marks]

(d).      Make a diagram 10 – 12 cm long of the reflex arc and label fully.  [7 marks]



Few candidates attempted this question  and those who did performed poorly.  In defining hormones many candidates just stated that they were chemical substances. They omitted to state their origin  i.e. that they are secreted by the endocrine glands and so they did not score the full marks.  Most candidates tabulated the differences between nervous coordination and hormonal coordination but could only give two differences. Expected answers include:

Differences between hormonal coordination and nervous coordination in humans

Hormonal Nervous
Transmission is chemical            

Transmission is electrical and chemical

Slow transmission                        
Rapid transmission
Response is wide spread            
Response localized
Target organs receive response    
Effector organs receive response
Long lasting response;                   
Short-lived response
Pathway not specific through     blood  

Pathway specific through nerve fibres

Candidates could not state the effects of over secretion and under secretion of thyroxine. Very poor diagrams of the reflex arc was made. Many of the diagrams were not titled, some candidates gave the title as diagram of a reflex action rather than the diagram of a reflex arc. In many cases the guidelines were drawn with free-hand and did not touch the structure to be labelled. Only two neurones were shown, in many cases the intermediate neurone was omitted and the motor neurone did not end up in an effector organ.
The expected answers and diagram are as follows:

Effects of over - secretion
- Over active/Hyperactive/irritable/nervous
- Excessive growth /gigantism;
- Loss of weight;
- Enlarged thyroid gland/exothermic goitre;
- Accelerated/increased heartbeat;
- Protrusion/bulging out of eyeball.
Effect 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/myxoedema;
- Goitre formation/hyperplastic goiter.

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