1. (a)     Explain the following terms:
            (i)   disease;                                                                                                            [4 marks ]
           (ii)   symptoms of diseases
   (b)     (i)  List two physical and two chemical barriers that prevent pathogens from
                  penetrating the body of an organism                                                                 [4 marks]
           (ii)    Explain how vaccination protects the body from contracting infectious
                   diseases                                                                                                           [5 marks]
   (c)     Distinguish between an antibody and an antigen.                                                  [4 marks ]
   (d)     Name the causative agents of:
            (i)   Malaria;
           (ii)    Cholera;
          (iii)    AIDS                                                                                                                [3 marks ]

 

observation

   Candidates could not correctly explain diseases but could explain the symptoms of diseases. 
The expected answer is:
Disease, is a condition in which the normal functioning of an organism or part of the body is  impaired.
Candidates were only giving examples of symptoms like headache for malaria fever, stomach pain for typhoid fever instead of defining it, as an effect which is observable, which is caused by irritation or  presence of a pathogen.
In 7(b) candidates could not understand the phrase physical and chemical barriers that prevent pathogens from penetrating the body of an organism, and so performed poorly in the question.
Again most candidates could not explain how vaccination protects the body from contracting infectious diseases; and could not state the difference between antibodies and antigens

 

They were however able to name the causative agents of Malaria, Cholera & AIDS but a lot of candidates lost their marks as a result of spelling mistakes especially in the spelling of Vibrio cholerae which was written as  vibro  cholera.  Those who got the spellings correct forget to underline the scientific names.
Expected answers include:
  (b)(i)  Physical barriers that prevent pathogens from penetrating the body of an organism:

• skin;
• hairs;
• cuticle;
• epidermis;
• bark;
• cell wall lining.                                                                                  

    
      Chemical barriers

• mucus;
• saliva;
• tears;

 

• gastric HCL and intestinal secretions;
• phenolic compound;
• gums;
• tannins;
• wax;   
• oily secretions/sebum.

 

 

 

How vaccination protects the body
(ii)   -    The vaccine/attenuated pathogen is administered into the body;

• the body responds by producing copious antibodies;
• the next time the body is exposed to the same antigen/infection/pathogen antigen;
• the memory cells allow a more rapid and heightened vigorous response to antibody production;
• protecting the body against future infections

 

( c )     Differences between antibodies and antigens
          Antibody                                                                                        Antigen:

• A protein molecule;                                               may not be a protein molecule;
• produced in response to a particular foreign;        stimulates formation of antibodies;

substance/antigen;

• usually found in the plasma fluid of the blood;      usually produced/introduced into the body;                   
• protective in function.                                            leads to an immune response/immunity.

  

• (i) Causative Agent of Malaria

     Plasmodium vivax/ Plasmodium falciparum/malaria/species
     (ii)    Cholera – Vibrio cholerae
     (ii)    AIDS – Human Immuno-deficiency Virus/HIV.