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AQA Biology GCSE
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Topic 3-infection and response
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Pathogens are
microorganisms
that
enter
the body and cause disease
Types
of pathogen
Bacteria
Viruses
Protists
Fungi
Bacteria
Very
small
living cells (about 1/100th the size of your body cells)
Can
reproduce
rapidly inside your body
Can make you feel ill by producing
toxins
(poisons) that
damage
your cells and tissues
Viruses
Not
cells
, they're
tiny
(about 1/100th the size of a bacterium)
Can
reproduce
rapidly inside your body
Live inside your
cells
and replicate themselves using the cells' machinery to produce many
copies
of themselves
Cell
damage
is what makes you feel
ill
Protists
Single-celled
eukaryotes
Some are
parasites
that live on or inside other organisms and can cause them
damage
Often transferred to the organism by a
vector
, which doesn't get the
disease
itself
Fungi
Some are single-celled, others have a body made up of
hyphae
(
thread-like
structures)
Hyphae can grow and
penetrate
human skin and the surface of plants, causing
diseases
Hyphae can produce
spores
, which can be
spread
to other plants and animals
Ways
pathogens can be spread
Water
Air
Direct
contact
Measles
Viral
disease spread by droplets from an infected person's sneeze or
cough
Causes a
red skin rash
and
fever
Can lead to serious complications like
pneumonia
or
encephalitis
HIV
Virus spread by
sexual contact
or
exchanging bodily fluids
Initially causes
flu-like
symptoms, then
no
symptoms for years
Attacks the
immune cells
, leading to
late
stage HIV infection (AIDS)
Tobacco
mosaic virus (TMV)
Virus that affects many plant species like
tomatoes
Causes a
mosaic
pattern on the leaves,
reducing
photosynthesis and plant growth
Rose
black spot
Fungus that causes purple/
black
spots on rose leaves, leading to leaves turning
yellow
and dropping off
Reduces
photosynthesis
and
plant growth
Spreads through
water
or
wind
Can be treated with
fungicides
and removing affected
leaves
Malaria
Caused by a
protist
Part of the
protist's
life cycle takes place inside
mosquitoes
, which act as vectors
Causes repeating episodes of
fever
, can be
fatal
Spread can be reduced by stopping mosquito
breeding
and using
insecticides
/nets
Salmonella
Bacteria
that causes food
poisoning
Infected people suffer
fever
,
stomach
cramps, vomiting and diarrhoea
Caused by
toxins
produced by the bacteria
Can be contracted from
contaminated
food, but poultry is
vaccinated
against it in the UK
Gonorrhoea
Sexually transmitted bacterial disease
Causes pain when
urinating
and
discharge
Originally treated with
penicillin
, but now strains are
resistant
Can be prevented by using
barrier contraception
Ways
to reduce/prevent disease spread
Being
hygienic
Destroying
vectors
Isolating
infected
individuals
Vaccination
Human
body's defences
Skin acts as a
barrier
and
secretes antimicrobial substances
Hairs
and
mucus
in nose trap particles
Trachea
and bronchi secrete mucus and have
cilia
to trap pathogens
Stomach
produces
hydrochloric acid
to kill pathogens
White
blood cells
Most important part of the
immune system
Can consume and digest pathogens (
phagocytosis
)
Produce
antibodies
specific to pathogens
Produce
antitoxins
to counteract toxins
Vaccination
Involves injecting small amounts of dead or
inactive
pathogens to stimulate
antibody
production
Allows
rapid
antibody response if exposed to live pathogens later
Has helped control many
communicable
diseases
Can prevent epidemics if enough people are
vaccinated
But don't always work and can have
rare
bad reactions
There are lots of
communicable diseases
that were once
common
in the UK (e.g. polio, measles, whooping cough, rubella, mumps, tetanus)
Smallpox no longer occurs at all, and
polio
infections have fallen by
99
%
Epidemics
Big outbreaks of
disease
Epidemics
Can be
prevented
if a large percentage of the population is
vaccinated
If a significant number of people aren't vaccinated, the disease can spread
quickly
through them and lots of people
will
be ill at the same time
Cons
of vaccines
Vaccines don't always work - sometimes they don't give you
immunity
You can sometimes have a
bad reaction
to a
vaccine
(e.g. swelling, or maybe something more serious like a fever or seizures)
Bad reactions to vaccines are very
rare
Deciding
whether to have a
vaccination
Balancing
the risk of catching the disease if you don't have a vaccine,
against
the risk of having a bad reaction if you do
Prevention
is better than
cure
Painkillers
Drugs that relieve
pain
, but don't actually tackle the cause of the disease or kill pathogens, they just help to
reduce
the symptoms
Cold
remedies
Don't actually cure colds, they just
reduce
the symptoms
Antibiotics
Kill or prevent the
growth
of bacteria causing the problem without
killing
your own body cells
Antibiotics
don't destroy
viruses
(e.g. flu or cold viruses)
The use of antibiotics has greatly reduced the number of
deaths
from communicable diseases caused by
bacteria
Developing
new drugs
1. Preclinical testing on human
cells
and
tissues
in the lab
2. Testing on live animals to test
efficacy,
toxicity
and find the best
dosage
3.
Clinical
trials on
healthy volunteers
and then people suffering from the illness
The law in
Britain
states that any new
drug
must be tested on two different live mammals
Some people think that animals are so different from humans that testing on animals is
pointless
Clinical
trials
1. Patients are
randomly
put into two groups - one gets the new drug, the other gets a
placebo
2. known as
double
blind
trial - the
patient
doesn't know if they're getting the drug or placebo, neither does the
doctor
3. The results are published after peer review
Monoclonal antibodies
Identical antibodies produced from
clones
of a single
white
blood cell
Producing
monoclonal
antibodies
1. Mouse injected with chosen antigen
2.
Fast-dividing tumour
cells from the lab fused with B-lymphocyte to create a
hybridoma
3.
Hybridoma
cells cloned to produce lots of
identical
cells that produce the same antibodies
Uses
of
monoclonal
antibodies
Can be used to target specific
cells
or
chemicals
in the body
Can be used in labs and research to measure chemical
levels
, test for
pathogens
, and locate specific molecules
Monoclonal antibodies do cause
more
side effects than were originally expected, such as fever, vomiting and low blood pressure.
Plants need mineral ions from the
soil
, and a lack of certain
ions
causes deficiency symptoms
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