Cambridge International A Level Biology Revision Guide

Cambridge International AS Level Biology
Answers to self-assessment questions
Answers to SAQs
Chapter 10
1 a infectious e.g. influenza, pneumonia
non-infectious e.g. lung cancer, COPD
b coronary heart disease, stroke
2 Faeces from infected person contain Vibrio
cholerae. These bacteria are transmitted
to uninfected people in drinking water,
contaminated food (e.g. vegetables irrigated
with raw sewage or food prepared by a
symptomless carrier), or when washing or
bathing in contaminated water.
3
10 13
10 6 = 10 million
4 Refugees rarely have access to proper
sanitation, clean water, or uncontaminated
food.
5 The visitor can drink bottled or boiled water,
and avoid eating salads and raw vegetables.
6 When a female Anopheles mosquito bites an
infected person she takes up some gametes
of the parasite. These develop into infective
stages which enter an uninfected person when
the same mosquito takes another blood meal.
7 The resistance of mosquitoes to insecticides
such as DDT and dieldrin; the difficulty of
controlling the breeding of mosquitoes
because they lay eggs in small bodies of
water; the resistance of some strains of
Plasmodium to anti-malarial drugs such as
chloroquine.
8 People can avoid being bitten by mosquitoes,
sleep under nets impregnated with
insecticide, use repellents, and use antimalarial
drugs as prophylactics (but not
those to which Plasmodium is resistant).
9 Many cases of AIDS are not diagnosed or
reported.
10 Condoms can split when in use or may not be
put on correctly.
11 Practise safer sex (e.g. use condoms); do
not use unsterile needles; have one sexual
partner; do not donate blood if at risk of HIV
infection; do not use prostitutes (male or
female); have a blood test to find out if you
are HIV+.
12 HIV is a blood-borne virus; blood donations
may not be screened or heat-treated for HIV.
13 It is important for people to know whether
they are HIV+ so that they can make sure they
reduce the chances of transmitting the virus
to others.
14 a The global distribution of HIV/AIDS is similar
to that of TB. Both are common in Sub-
Saharan Africa and in Eastern Europe, India
and China.
b HIV/AIDS decreases the number of
T-lymphocytes, weakening the ability of the
body to mount an effective immune response
against HIV and other pathogens. About onethird
of the human population is infected
with M. tuberculosis, and this infection may
progress to cause the symptoms of TB if the
immune system is weakened by HIV infection.
15
Pathogen
Method of
transmission
Global
distribution
Incubation
period
Site of action
of pathogen
Clinical
features
morbillivirus
airborne droplets sneezed or coughed
by an infected person and breathed in
by an uninfected person
worldwide – highest number of cases
in Africa, South-East Asia, Indian
subcontinent, Middle East
8 to 14 days
respiratory tract (trachea and bronchi)
fever and rash
Cambridge International AS and A Level Biology © Cambridge University Press 2014