Observation

Many candidates interchanged the answers for question 1 (a) while some referred to blood as heart; Guinea pig as organ; Hibiscus flower as flower; human skeleton as organ; Plasmodium as system and lost some valuable marks. Many candidates scored good marks in the definition of Homeostasis. Majority of the candidates do not know how the kidney maintains acid-base balance of the blood; some candidates were able to state the factors that affect the functioning of the kidey.

The expected answers are:

1. (a)  Levels of Organisation

          Organisms/Structures                                 Level of Organisation

NOTE: Spellings of levels of organisation must be correct to score.

 (b)  Homeostasis
Is the process by which the internal environment of the body; is regulated; so as to maintain a steady state/balance; thereby preventing the damage of the cells.          

                              
(c) (i)   How the kidney maintains acid – base balance of the blood
- The pH of human blood is neutral/between pH 7.35 to 7.45; 
- anything above/below this range is dangerous to the body;
- when the body fluid/blood becomes acidic; the cells of the distal convoluted tubule will reabsorb more hydroxyl ions (OH-) from the urine;
- more hydrogen ions (H+) are excreted; making the urine acidic;
- if the body fluid/blood becomes basic/above pH8, hydroxyl content of the blood gets higher;
- less hydrogen ions are produced by cells of the second/distal convoluted tubules;
- more hydroxyl ions are produced and excreted with the urine/making the urine basic.

 (ii)  Factors that affect functions of the kidney
- Environmental temperature; in cold days/low temperature; there is the tendency to urinate more; more water is lost through the kidney/through frequent urination; thereby putting the kidney under much stress; on hot days/high temperature less water is lost through urination.                                       
-  Drugs; diuretic drugs /any correctly named drug; bring about excessive loss of water from the kidney; causing frequent urination.                                                                     
-  Fresh water habitat; endosmosis occurs; leading to frequent inflow of water; resulting in the production of dilute/hypotonic urine.                                                      
Marine habitat; exosmosis occurs; leading to frequent loss of water into the environment; resulting in the production of hypertonic/highly concentrated urine.           
Arid/desert habitat; more water is absorbed by the kidney; resulting in semi-solid urine/uric acid. 

-  Diseases; nephritis/kidney stone/any correctly named disease; bring about/lead to malfunctioning of the kidney; e.g. passing out urine with protein/blood cells/ passing urine with great difficulty/any correctly named symptom.