waecE-LEARNING
Biology Paper 2,Nov/Dec 2011  
Questions:   1 2 3 4 5 6 7 8 Main
General Comments
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Question 8

                (a)   State three ways by which water is of importance to mammals.                             [3 marks ]
                (b)    Name:
                         (i)   two structures in plants;
                         (ii)  three structures in mammals; that excrete water.                                              [5 marks ]

                 (c)    How does the mammalian body respond to low water content?                           [ 8 marks ]
                 (d)    List four plant  hormones.                                                                                              [ 4 marks ]

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comment

                  This was the more popular question in this section and candidates who attempted it
                  performed fairly well.

                  Most candidates could state three ways in which water is of importance to mammals e.g.
                  temperature  regulation e.t.c. but some candidates wrote domestic uses of water and lost   
                  marks.

                  Candidates could properly name structures that excrete water in mammals and plants
                  and   name four plant hormones but lost some marks due to spelling errors. 
                  In describing how  the mammalian body responds to low water content a lot of candidates
                  performed poorly and scored low marks.

                   Expected answers include:

                    Response to low water content in the mammalian body

         -     the hypothalamus will detect low water high/osmotic pressure in the blood;
         -     nervous impulses will be sent to the posterior pituitary gland; to release antidiuretic
               hormone/ADH into the blood;
         -     the ADH increases the permeability of the kidney tubules to water;
         -     more water will be reabsorbed from the kidney tubules into the blood capillaries; the
               blood’s osmotic pressure will be reduced;
          -    little amounts of urine/ concentrated urine/hypertonic urine is produced;
          -     as hypertonic urine is produced;  more water will be absorbed from the colon/ rectum
                into the blood;
          -    the  skin will also reduce the production of sweat in order to conserve water.
                            

 

 

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