Summative Practice 11 – Question 4 (Form 4 Biology Textbook Exercise and Answer)

Question 4:
Figure 1 illustrates the changes in the antibody levels in the blood of individuals X and Y for a specific period of time.

(a)(i) What type of immunity did individuals X and Y acquire?
(ii) State the substance injected in individuals X and Y.
(iii) Explain the differences in the content of the substances you mentioned in (a)(ii).

(b)(i) On the graph curves of individuals X and Y, mark with an arrow, the time of the second injection is given.
(ii) Why do individuals X and Y need a second injection?
(iii) Based on the graph curves for individuals X and Y, state two differences in the immunity achieved by individuals X and Y.

X: Artificial passive immunity
Y: Artificial active immunity

X: Antiserum
Y: Vaccine

Antiserum is blood plasma that contains antibodies or antitoxins for a particular disease. Vaccine is dead or weakened antigens which are injected into a person’s body to induce his/her immune system to produce the required immunity.


• Individual X: The second injection is required to increase the quantity of antibodies beyond the immunity level because the quantity of the antibodies drops below the immunity level after a
period of time.

• Individual Y: The second injection is needed to induce more antibodies beyond the immunity level because the first dose is insufficient for the individual to achieve the required immunity level.

• The immunity acquired by individual X is immediate while the immunity acquired by individual Y is slow.

• The period of immunity for individual X after reaching immunity level is temporary but for individual Y, it is permanent.

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