Health Science Paper 2, May/June 2011  
Questions: 1 2 3 4 5 Main
General Comments

Question 5

  (a)    State two functions each of the following organs:
         (i)   kidney;
        (ii)   lungs;
       (iii)   skin.                                                                                                                  [6 marks]

(b)    Describe the mechanism of inhalation in humans                                                   [6 marks]

(c)    What is meant by assimilation?                                                                               [2 marks]

(d)     Explain the processes of
         (i)   ultra-fitration
         (ii)   selective re-absorption                                                                                    [6 marks]



This question was attempted by few candidates and their performance was poor. 
In part (a)(i) candidates could not correctly state functions of the kidney, in (a) (ii) and (iii) few candidates that attempted the question correctly stated functions of lungs and skin. 
In part (b) candidates could not correctly describe the mechanism of inhalation in humans.  In part (c) candidates took assimilation as process of digestion instead of uptake of digested food into the body cells.  In part (d) candidates could not correctly explain
(i) ultra-fitration
(ii) selective re-absorption.
However, the expected answers were as follows:

5(a)    Functions Kidney

  •    removes nitrogenous waste/excretion
  •    regulates water content of blood/osmoregulation
  •    maintains acid base balance.

       (ii)      Function   Lungs

  •    gaseous exchange
  •    excretes carbondioxide
  •    organ for intake of oxygen.

      (iii)      Function skin

  •  excretion
  •  protection
  •  regulates body temperature
  •  formation of vitamin D
  •  sense organ

(b)     Mechanism of inhalation

  •   the external intercostals muscles contract
  •   and the internal intercostals muscles relax
  •   this causes the ribs to move up and act
  •   to make the diaphragm of the flatten
  •   this makes the volume of the thorax to increase
  •   and the air pressure decreases
  •   forcing air into the lungs.

(c)      Assimilation
           is the uptake/absorption of the end products of digestion;
           into the body cells/tissue.
(d)(i)   Explanation Ultra – filtration and selective reabsorption

           Ultra- filtration:  under pressure from the glonerulus to Bowman’s capsule during
           which blood cells and blood proteins are retained, but some food substances
           water, urea and nitrogenous compounds pass through.
   (ii)   Selective re-absorption:  as glomerular filtrate passes down the kidney tubule to
          the collecting duct useful substances are re-absorbed from the filtrate and
          unwanted substances retained in the filtrate to form urine.             

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