Cambridge International A Level Biology Revision Guide

Chapter 11: Immunity
Concentration of antibody in blood of fetus or infant
0
birth
2 8 0
Time after conception / months
total antibody
infant antibody
maternal antibody
Figure 11.14 The concentrations of antibody in the blood of a
fetus and an infant.
12
Colostrum, the thick yellowish fluid produced by a
mother’s breasts for the first four or five days after birth,
contains a type of antibody known as IgA. Some of these
antibodies remain on the surface of the infant’s gut wall,
while others pass into the blood undigested. IgA acts in
the gut to prevent the growth of bacteria and viruses
and also circulates in the blood. This is natural
passive immunity.
The features of active and passive immunity are
compared in Table 11.2 and Figure 11.15.
Vaccines
A vaccine is a preparation containing antigens which
is used to stimulate an immune response artificially. It
may contain a whole live microorganism, a dead one, a
harmless version (known as an attenuated organism),
a harmless form of a toxin (known as a toxoid) or a
Immunity
Features
Antigen
encountered
Immune
response
Time before antibodies appear in
blood
Production of
memory cells
Protection
active yes yes 1–2 weeks during an immune response yes permanent
passive no no immediate no temporary
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Table 11.2 Features of active and passive immunity.
Active immunity
Immunity developed after contacting
pathogens inside the body.
Passive immunity
Immunity provided by antibodies or antitoxins
provided from outside the body.
Natural
infection
Artificial
injection of live or
attenuated pathogen
Natural
antibodies from a mother in breast
milk or across the placenta
Artificial
injection of antibodies
or antitoxin
Figure 11.15 Active and passive immunity.
Natural immunity is immunity gained by being infected
(active) or by receiving antibodies from the mother
across the placenta or in breast milk (passive).
Artificial immunity is immunity gained either by
vaccination (active) or by injecting antibodies (passive).
Vaccination is giving a vaccine containing antigens for
a disease, either by injection or by mouth; vaccination
confers artificial active immunity.
QUESTIONS
11.13 Explain the difference between artificial active
immunisation (vaccination) and artificial passive
immunisation.
11.14 a Explain the pattern of maternal and infant
antibody shown in Figure 11.14.
b Explain the advantages of natural passive
immunity for newborn infants.
11.15 Explain the difference between immunity to a
disease and resistance to an antibiotic.