Download ce_ch20_e

New Biology — a modern approach
Answers to Continuous Evaluation
20 Defence against diseases
Class Practice
20.1 What is a disease?
1. F
2. T
3. F
4. F
20.2 Body defence
Column P
Column Q
Column R
Non-specific defence ●
●
First line of defence
●
●
by white blood cells
●
●
Second line of defence
●
●
by immune system
●
Last line of defence
●
●
by natural barriers
Specific defence
20.3 Non-specific defences
A.
B.
C.
Part of the body
Substance(s) produced
1.
Sebaceous glands
sebum
2.
Eyes
tears
3.
Mouth
saliva
4.
Stomach
5.
Vagina
1.
2.
3.
4.
1.
2.
F
T
F
T
A
D
3.
4.
B
B
gastric juice
acid
20.4 Specific defences
A. 1. F
2. C
3. G
4. B
5. E
© Aristo Educational Press Ltd 2007
1
Answers to Continuous Evaluation
B.
6.
7.
D
A
1.
2.
3.
B
D
A
New Biology — a modern approach
20.5 Immunity and vaccination
1. T
2. F
3. F
4. F
5.
T
Exam Practice
A.
Multiple Choice Questions
1. C
2. A
3. D
4. C
5. C
6. B
7.
8.
9.
10.
B.
C
C
B
B
Structured Questions
1. (a)
© Aristo Educational Press Ltd 2007
2
New Biology — a modern approach
Answers to Continuous Evaluation
(b) A vaccine is made from dead or weakened pathogens. When a vaccine is
administered to a person, it causes the body to produce its own antibodies.
(c) After the first injection, antigens from the dead or weakened pathogens in the
vaccine stimulate the lymphocytes to produce antibodies. Afterwards, the antigens
are memorised by the memory cells. Subsequent exposure to the same type of
antigen will initiate rapid production of a large amount of antibodies specific to
that antigen. The higher concentration of antibodies produced is maintained for a
longer period of time.
2.
(a) 5 weeks
(b)
antibody level
in blood
(arbitrary units)
immune response
no immune response
time (weeks)
1st injection
2nd injection
(c)
3.
1st injection
2nd injection
- Antibodies are not produced
immediately/rapidly.
- A small amount of antibody are
produced.
- The concentration of antibody drops
- Antibodies are produced
immediately/rapidly.
- A larger amount of antibodies are
produced.
- The higher concentration of antibody
shortly after the injection.
(Any two)
produced lasts longer.
(Any two)
(d) give a booster injection
(a) (i) cilia
(ii) The cilia can sweep the mucus and pathogens upwards.
(b) (i) through the mouth/the food eaten
through the skin/the wounds
© Aristo Educational Press Ltd 2007
3
Answers to Continuous Evaluation
New Biology — a modern approach
(ii) Gastric juice in the stomach contains acid which kills the pathogen.
Clotting of blood and phagocytosis prevent the pathogens from getting into
4.
(a)
(b)
(c)
(d)
the body.
It is the non-specific defence mechanism.
The mucus in respiratory tract traps the virus which is wafted away by the cilia.
The phagocytes engulf the virus.
through contact/inhaling droplets from coughs or sneezes
It is because the antibody level for acting against the specific type of virus is still
high in his father’s body. The virus will be removed quickly and the disease cannot
develop again.
It is because the virus causing the common cold of another type.
The action of the antibody is specific and so the antibody against the previous virus
cannot combat the now one.
(e) - build up good body resistance against disease through a balanced diet and regular
exercise.
- maintain good personal hygiene. (Any other reasonable answers)
C.
STS Connections
1. (a) Non-specific defence. Phagocytes.
(b) Saliva in the mouth cavity contains lysozymes for destroying a small proportion of
the bacteria.
2.
The stomach secretes acid for killing the bacteria.
(c) The statement is correct. Antibiotics are effective only on bacteria but not on
viruses.
(d) - Wash hand thoroughly before handling food, eating and after going to the toilet.
- Maintain good indoor ventilation.
- Cook food (especially seafood and shellfish) thoroughly.
(any other reasonable answers)
(a) The antigens in the fluid stimulate the lymphocytes to produce antibodies to act
against the pathogens but the speed of production and level of antibodies were low.
Hence, the boy caught the disease. After some time, the level of antibodies was
high enough to eliminate the pathogen.
(b) The antigens of the pathogens for smallpox are similar to those of cowpox. The
lymphocytes have a memory for the antigens of cowpox. As a result, the
lymphocytes are stimulated to produce antibodies quickly and to a very high level
so as to eliminate all the pathogens.
© Aristo Educational Press Ltd 2007
4