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20 Defence against diseases
20.1 What is body defence? (Book 3, p.86)

(1)
Body
defence
(身體防衛) is
the protective function of our body against diseases.

(2)
Pathogens
are micro-organisms which
cause diseases. Examples include bacteria and viruses.

The two main types of defence methods:
1
those that prevents pathogens from entering the body
2
those that fight against the invading pathogens
 Our body protects us against
pathogens
20.2 What are the non-specific defence methods? (Book 3, p.87)

(3)
Non-specific
defence
methods
(非專一性的防衛方法)
prevent all types of pathogens from causing diseases. Their actions are non-specific
(非專一性的).

Possible entrances through which pathogens may enter our body:
 Reproductive systems
 Respiratory system

 Digestive system
Physical barriers and chemical barriers form the (4)
of
defence
first
line
(第一道防線).
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33
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Physical barriers (Book 3, p.87)

(1)
Physical
barriers
(物理屏障) are the physical
structures that prevent
pathogens from entering the body.

Physical barriers include:
Skin covers the whole body. Its outer layer of
(2)
dead
cells
in the
epidermis stops the entry of pathogens.
 Skin
In the ciliated epithelium of the respiratory tract,
(3)
mucus
from the mucus-secreting
cells trap pathogens. The beating action of
(4)
cilia
moves the trapped pathogen
to the pharynx for swallowing or coughing out.
 Respiratory tract
Chemical barriers (Book 3, p.87)

(5)
Chemical
barriers
(化學屏障)
are chemical secretions that may kill or
stop the growth of pathogens, hence preventing them from entering the body.

Chemical barriers include:
(6)
Sebum
secreted by the
sebaceous glands of the skin acts as a natural
(7)
antiseptic
(消毒劑)
to kill
pathogens on the skin.
 Skin
34
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Gastric juice secreted in stomach contains
(1)
hydrochloric
acid
to kill
pathogens in food.
 Stomach
(2)
Tears
secreted by the tear glands
of the eyes acts as a natural antiseptic to kill
pathogens on the conjunctiva.
 Eye
Phagocytosis (Book 3, p.88)


(3)
Phagocytosis
(4)
phagocytes
is the process in which pathogens are engulfed by
(吞噬細胞).
Phagocytes kill the engulfed pathogens by digesting them with (5)
enzymes
.
 Phagocytosis and digestion of a pathogen
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Inflammatory response (Book 3, p.89)

Events in an inflammatory response:
1
(1)
2
wound
on skin
Arterioles in the infected area
dilate
.
Blood capillaries (2)
pathogen
increases
their permeability.
phagocyte
3
More blood flows into the infected area.
4
More (3)
phagocytes
come out
of the capillaries to engulf and kill the
capillary
invading pathogens.
 Inflammatory response

(4)
Inflammation
painful. (5)
(發炎)
Pus
occurs when the infected area becomes red, swollen and
(膿) may form
inside the wound.
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Section concept diagram (Student’s Book 3 p.90)
Quick check (Student’s Book 3 p.90)
20.3 What are the specific defence methods? (Book 3, p.91)

(6)
Specific
defence
immune responses (免疫反應) in which (7)
methods
antibodies
(專一性的防衛方法) are the
(抗體) are
produced to act
against antigens.

They are more powerful than the non-specific methods.
Production of antibodies (Book 3, p.91)

(8)
(9)
Lymphocytes
antigens
in blood and lymph nodes detect
(抗原)
on the surfaces of pathogens to
produce antibodies.

Each kind of antibodies is (10)
in action.
36
specific
(專一性的)
 The Y-shaped antibodies
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
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Antibodies can act against pathogens in the following ways:
1 (1)
Lysis
(溶菌作用) of
a pathogen
antigen
antibodies
hole
pathogen
(bacterium or virus)
2 Helping in (2)
antibodies attach to
pathogen and start
processes to make holes
pathogen is lysed
(被溶解) and killed
phagocytosis
phagocyte
pathogen
antibody
antibodies attach to
the pathogen
phagocyte detects and engulfs
the pathogen
3 Making pathogens into (3)
antibodies
4 Acting as (4)
clumps
pathogens
antitoxins
antibodies
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pathogen is killed by
phagocytosis
(抗毒素) to
toxins
pathogens stuck together
by antibodies cannot
reproduce or enter cells
neutralize toxins
antibodies act as antitoxins
to neutralize toxins
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Primary and secondary immune responses (Book 3, p.93)

When a type of pathogen enters the body for the first time, it stimulates the production of
antibodies. This response is called the (1)

Some lymphocytes become (2)
primary
memory
response
cells
(原發反應).
to memorize the kind of
pathogens that have entered the body.
antigen
undergo
cell
divisions
first
encounter
produce antibodies
against antigens
pathogen
lymphocyte
activated by
antigen
become memory cells
 The primary response

Next time when the same pathogen enters the body, it is recognized by the memory cells which
then quickly initiate a (3)

secondary
The secondary response produces a (4)
antibodies of the same kind in much (5)
response
larger
shorter
(繼發反應).
amount of lymphocytes and
time to destroy the pathogen.
 Changes in antibody level in the blood during primary and secondary responses to the
same pathogen
38
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Quick check (Student’s Book 3 p.94)
STS connection 20.1 Enhancement of immunity by the intake of ‘health food’ (Student’s Book 3 p.94)
E 20.4 What is the principle of vaccination? (Book 3, p.95)

(1)
Vaccination
(疫苗接種) is the
injection of controlled amounts of a weakened or dead
pathogen, or an altered form of a pathogen, which has been made harmless.

These injections, called (2)
vaccines
(疫苗),
contain the antigens normally present on
the surface of the pathogen.

Vaccination makes use of the specificity and memory abilities of the immune system. The
vaccine produces a (3)
primary
active pathogen of the vaccine will lead to a (4)
response
. Any subsequent infection by the
secondary
response
, giving
enhanced resistance to the disease.
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STS connection 20.2 Stories of the development of vaccination
(Student’s Book 3 p.95; Activity Book 3 p.45)
Section concept diagram (Student’s Book 3 p.96)
Quick check (Student’s Book 3 p.96)
STS connection 20.3 Relation of immunization programmes to the control of infectious diseases
(Student’s Book 3 p.97; Activity Book 3 p.48)
Review (Student’s Book 3 p.97)
Summary concept diagram (Student’s Book 3 p.98)
Note:
In the 18th century, many people died of an infectious disease called smallpox (天花). Edward Jenner (17491823), a
British doctor, noticed that milkmaids never came down with smallpox but a similar disease called cowpox (天花). This
inspired him to put some pus collected from the boils (皮下膿腫) of a cowpox patient into the wound of a healthy boy. The
boy did catch cowpox but it was only a mild disease. When the boy had recovered, Jenner put some pus collected from
the boils of a smallpox patient into the wound of that boy again. Interestingly, the boy was protected against smallpox.
The basis of vaccination was formed on these experiments.

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39
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 Practice question
Answer the questions below with reference to the following article.
China is ready to begin the second phase of human trial on vaccines against SARS
(嚴重急性呼吸系統綜合症). The vaccines,
containing inactivated SARS-causing viruses, were
proven effective in monkeys. In 2004, the vaccines were put on first human trial. None of the
healthy volunteers had abnormal reactions and SARS-neutralizing antibodies were detected in
their blood. In the coming trial, researchers hope to find out how long the antibodies can remain
in the volunteers.
a
Explain why SARS-neutralizing antibodies were detected in the blood of the volunteers.
(2 marks)
With the injection of vaccines, the antigens of the inactivated SARS-causing viruses (1m)
stimulate the body to produce a primary response in which antibodies are produced (1m).
E b
How may the vaccines mentioned in the article provide protection against SARS? (4 marks)
With the injection of vaccines, memory cells are produced which can memorize the type
of pathogen (1m).When the body is infected later on by the SARS-causing viruses again,
the body will develop a secondary response (1m). A larger amount of specific antibodies
(1m) are produced in a shorter time (1m). Therefore, the body will show enhanced
resistance to the SARS.
E c
Apart from inactivated SARS-causing viruses, suggest one other active ingredients for
making vaccines against SARS.
(1 mark)
Dead SARS-causing viruses / Pieces of DNA of the SARS-causing viruses. (1m)
E d
Explain why the volunteers chosen for the trials must not be sick at the time of vaccination.
(2 marks)
When the volunteers are sick at the time of vaccination, the immunity of their
bodies are weak (1m). They may be infected by the inactivated viruses (1m).
Total: 9 marks
－ END －
40
Certificate Biology - New Mastering Basic Concepts
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