KEEPING HEALTHY
How our bodies defend themselves
against infectious diseases
Summary of Specification content
• Pathogens cause disease.
Learning Outcomes
• Explain how pathogens cause disease.
• Carry out and describe aseptic
techniques.
Pathogens
• Microorganisms that cause infectious
disease are called pathogens.
• Disease occurs when large numbers of
pathogenic micro-organisms enter the
body.
• Pathogens can be bacteria or viruses
Bacteria
• Very small
• Reproduce rapidly
• Produce toxins that make you feel ill
• E.coli produces toxins that cause fever symptoms
when we have food poisoning.
• Cause illnesses such as
• Tuberculosis
• Cholera
• Typhoid
Viruses
• Smaller than bacteria
• Invade cells, reproducing inside them
and damage them.
• This causes damage to tissues
• Examples
• Polio
• Flu
• Measles
• Cold
Spreading Disease
• Diseases can be spread by
• air
• In food
• In liquids
• Contact (touching someone else)
• Good hygiene can help prevent the
spread of disease
Pupil Activity
• Look at the pictures of bacteria, viruses
and fungi and link these to the diseases.
How Science Works:
• Video clip:
www.bbc.co.uk/learningzone/clips
• Clip 2883 – the importance of hand washing in
food hygiene
• Duration: 04:52
• An investigation into the best way to wash hands to
reduce the risk of food poisoning. Hands washed
thoroughly with soap have a significantly reduced
number of bacteria.
• Clip 207 – microbes and the human body
• Duration: 03:12
• A microbiologist talks about the microbes which live on
our unwashed hands and in our nose and throat.
Aseptic techniques
• Use agar plates to compare the growth of micro-
organisms from unwashed and washed hands
• Draw a line on the bottom of your agar plate
• Write “before” on one side and “after” on the
other
Before After
Aseptic techniques
• Lift the lid of the agar plate at an angle and press
the thumb of your right hand onto the agar.
• Close the lid
• Wash your hands with the hand wash at the back
of the lab
• Alternatively you could just use water, antibiotic hand gel or a
hand wipe.
• Lift the lid of the agar plate at an angle and press
your now “clean” thumb of your right hand onto
the agar.
• Write a brief description of what you have done
and draw a diagram of the plate ready for
recording your results.
Summary of Specification content
• Semmelweiss recognised the
importance of hand- washing to
reduce the spread of infection.
Learning Outcomes
• Describe the work of Semmelweiss and
link to results of class investigations.
Semmelweiss.
• Semmelweiss recognised that infection could
be transferred from person to person.
• He insisted that doctors wash their hands
before examining patients.
• This greatly reduced the number of deaths
from infectious diseases in his hospital
• His work demonstrated that hand-washing
could drastically reduce the number of women
dying after childbirth.
• At the time he was ignored because people
did not know that diseases were caused by
pathogens that could be killed
How Science Works: Semmelweiss
• Worksheet 1:
• Read the diary entries - Highlight an observation,
hypothesis, the independent variable and
conclusion that Semmelweis made
• Worksheet 2:
• read the information on Semmelweis and answer
the questions that follow
Semmelweiss – Worksheet 1
• Observation
Semmelweis Jun 09 F Qu 5.
• 5(a)(i) 12 correct answer with or without working: if
answer incorrect evidence of (number of deaths) × 6
• 5(a)(ii) (ward 2) more deaths / infections on ward 1 or
less deaths / infections on ward 2
• 5(b)(i) both bars correctly plotted ie plots in spaces
between 2.8 and 3.2 and 0.8 and 1.2 ignore width and
shading
• 5(b)(ii) less deaths / infections 1
• 5(b)(iii) bacteria / microbes / infection killed / washed off
Louis Pasteur
How Science Works
• Pasteur’s experiment
• Why did Pasteur boil the nutrient broth?
• to kill (micro)organisms / bacteria / microbes
• to sterilise
• Because of the shape of the flask, no
microorganisms grew even after several years.
• (micro)organisms / they could not enter (the broth / flask)
• (micro)organisms / they get trapped / stuck (in the bend)
• Pasteur repeated the investigation several
times. Why is it useful to repeat a scientific
investigation several times?
• (more) reliable
• to check if anomalous / consistent (same every time)
• After several years, some of Pasteur’s flasks
were tilted so that the broth flowed to point X.
The flasks were then returned to the upright
position and left for a few days.
• Explain why microorganisms grew in
the broth.
• microorganisms now enter (the broth / flask)
• microorganisms from air / bend / neck / x
• food / nutrients / energy source for microorganisms
(in broth)
• This investigation provides evidence for
the theory of
• biogenesis
Summary of Specification content
• Microbes can reproduce rapidly inside
the body and produce toxins that
make us feel ill.
• The body has different ways of
protecting itself against pathogens.
• White blood cells ingest pathogens and
produce antibodies and antitoxins.
Learning Outcomes
• Describe ways in which the body
defends itself against disease.
• Explain how microbes make us feel ill
and how viruses damage cells.
• Describe the actions of white blood
cells using terms ‘ingest’, ‘antibodies’
and ‘antitoxins’.
Suggested pupil activities
• Task:
• Label diagram to show how body
prevents entry of microbes.
• Compare viral and bacterial infections.
How Science Works:
• Use microscope or bioviewers to view
blood smears.
• Draw diagrams or cartoon strip to show
actions of white blood cells.
Immune System
• The immune system is the second line of
defence
• White blood cells help defend against disease by:
• They engulf and digest the microbe
• They produce antibodies to neutralise the microbe
• They produce antitoxins to neutralise the poisons produced
by microbes
Phagocytosis
• Phagocytes can move out of the
capillaries to the site of infection
• They engulf the infecting pathogens
and kill them by digesting them.
White Blood Cells
• Video clip:
www.bbc.co.uk/learningzone/clips
• Clip 1838 White blood cells
• Duration: 01:09
• Our white blood cells help our immune system by
engulfing foreign cells.
Antibody Production
• Lymphocytes
• are white blood cells formed in lymph nodes.
• Produce antibodies or anti-toxins in response to a
pathogen (antigens)
• A different antibody is produced for each antigen
Antibody Production
• Lymphocytes can memorise the
antigens that the body has been
exposed to.
• this allows antibodies to be produced
faster if reinfected
• Some antibodies remain in the blood to
give a long term protection
Summary of Specification content
• Immunity and action of antibodies.
• Vaccines – what they are and how
they work.
Learning Outcomes
• Explain the processes of natural and
acquired immunity.
• Evaluate the advantages and
disadvantages of being vaccinated
against a disease, eg the measles,
mumps and rubella (MMR) vaccine.
Tasks
• Card sorting exercise to sequence how
a vaccine can give immunity to a
disease.
• Role play on whether to give your child
vaccinations.
• How Science Works:
• Consider the actions of Dr Wakefield and the MMR
vaccine.
• Homework – research Edward Jenner.
Antibodies and Antigens
• An antigen is a protein
• foreign to an individual,
• It triggers a response by some white blood cells
• An Antibody is a protein
• which are secreted by WBC
• They are specific to the antigen that is present.
• Antibodies destroy the cells bearing the antigen
Natural Immunity
• Active
• This is when antibodies are produced by a person
when needed
• Passive
• passed from the mother to the infant whilst breast
feeding
Acquired Immunity
• Two methods
• A vaccine with dead or harmless microbes is
injected; the white blood cells are stimulated to
produce antibodies
• This is called active immunity
• The antibodies are injected directly into the body
• This is called passive immunity
Immunisation
• Introduction of a mild or dead form of
the pathogen
• Stimulates immune system to respond
• Production of anti-bodies
Immunological Memory
• After an antigen has been
encountered, memory cells remain in
the body
• Antibodies are produced very quickly if
the same antigen is encountered a
second time.
• This memory provides immunity
following a natural infection and after
vaccination.
Vaccines
• A vaccine contains antigens derived from a disease•
•
•
•
causing organism.
These antigens stimulate the white blood cells to
produce antibodies.
The memory cells remain in the blood
when the disease causing organism is encountered,
the rapid response is triggered which makes a person
immune.
Vaccines may be produced against bacteria and
viruses.
Immunisation- Dilemmas
MMR: How safe do you think it is?
• The largest study to date of the MMR vaccine
suggests that it is safe (May 2001)
• Researchers in Finland, who followed two million children for
two years failed to find a link between the combined measles
mumps and rubella jab with autism or bowel disease.
• However, a separate report claims that the
MMR vaccine was not tested properly before
being introduced.
• How safe do you think this vaccine is?
• Do the benefits of the MMR vaccine outweigh
the perceived risks?
Pupil Activity
• Read through the sheet on the MMR
vaccination
• Make a list of the pros and cons
• If you were faced with the decision
• would you vaccinate your child with the MMR
vaccination?
• Would you recommend to a close friend / family to
immunise a child with the MMR vaccination?
MMR PPQ BLY1H Jun 09 Qu 2
• 2(a)
• antibodies allow antitoxins / memory cells do not allow antigens
• Immune
ignore protection allow resistant
• 2(b)(i)
• fell
• numerical qualification to zero / nothing / by 100%
stopped in 1995
• 2(b)(ii)
allow
• (no)
• % vaccination fell or when no vaccination
• but autism numbers did not fall / stayed high / increased
• or
• ‘(yes)
• might support it if time lag between vaccination and autism symptoms’ /
‘time lag for diagnosis’
• 6 year time lag quantified (1)
FLU PPQ BLY1 H Jun 09 Qu 4
• 4(a) any two from
• live inside / infect body cells
• difficult for drugs to enter (body) cells / drug would kill
(body) cell
• antibiotics ineffective against viruses
• viruses mutate
• 4(b)(i) 420
• correct answer with or without working
• if answer incorrect evidence of number of deaths. × 7
or 60 seen gains 1 mark
• ignore 6 000 000
FLU PPQ BLY1 H Jun 09 Qu 4
• 4(b)(ii) any three from:
• virus / flu mutates
• people no longer / not immune
• white blood cells / memory cells / immune system
•
•
•
•
do not recognise virus
relevant reference to antibodies / antigens
current vaccine ineffective or no vaccine
available then or takes time to develop new
vaccine
conditions less hygienic / lack of hygiene
people in poor health (following world wars)
Summary of Specification content
• Use of medicines to relieve symptoms.
• Investigating the action of disinfectants
and antibiotics; aseptic techniques;
incubation temperatures.
Learning Outcomes
• Use aseptic techniques and explain the
precautions taken when handling
microorganisms.
Aseptic techniques
• Agar is a growth medium for micro
organisms
• Uncontaminated cultures of
microorganisms are prepared by
• Sterlisation of petri dishes and culture medium
• Sterilisation of inoculating loops
• Transferring microorganisms
• Sealing the petri dish
• Read through the guidance on preparing
uncontaminated cultures.
Summary of Specification content
• Use of antibiotics – how they work and
problems of overuse.
• Antibiotic resistance, eg MRSA.
• Mutations lead to resistant strains of
pathogens which can spread rapidly.
• Development of new antibiotics to
combat resistant bacteria.
Learning Outcomes
• Explain how antibiotics work.
• Explain how the treatment of disease has
changed due to understanding the action of
antibiotics and immunity.
• Explain the difficulty in developing drugs that
kill viruses without damaging body tissues.
• Evaluate the consequences of mutations of
bacteria and viruses in relation to epidemics
and pandemics.
• HT only
Explain what we should do to slow down the
rate of development of resistant strains of
bacteria.
Outbreaks of disease
• Epidemic is a local outbreak of a
disease
• Pandemic is a global outbreak of a
disease
• Mutations in bacteria and viruses,
global travel and antibiotic resistance
contribute to outbreaks of disease.
Treatment of disease
• Some drugs do not fight the disease
they just relieve the symptoms
• Painkillers are drugs that relieve pain – they reduce
the symptoms of the cold
• Antibiotics are chemicals which kill infectious
bacteria.
• E.g. penicillin – breaks down the cell wall
• As viruses infect our own body cells,
antibiotics are not effective against them
• Vaccinations can offer protection against
bacterial and viral infections
Advantages and disadvantages on
vaccinations
• Advantages
• Help to control
infectious diseases
• Prevent epidemics
• Disadvantages
• Don’t always give
immunity
• Bad reactions to
vaccines
Antibiotic resistance
• Some bacteria such as MRSA can
develop resistance to antibiotics.
• An increase in antibiotic resistance has
been seen due to the overuse of antibiotics
How Science Works
• Antibiotic resistance
• Research MRSA and C. difficile infections and
treatment.
• Research flu pandemics.
• Draw a timeline to show how treatment
of disease has changed over the years.
Viruses and Disease
• Measles is caused by one virus, if you
catch measles you are unlikely to
catch it again in your lifetime
• The common cold is caused by a
variety of viruses, which have the ability
to change and mutate. Each virus has
the ability to cause the common cold,
you build up an immunity to them one
at a time.
Jun 10 (H) Qu 3
• 3(a) worldwide or several countries (outbreak)
• 3(b)
• any three from
• new strain of flu / virus changes / virus different
• vaccination not effective or new vaccine not yet developed
• antiviral drugs not effective / not yet developed
• people not immune to it
• virus not recognised by white blood cells / antibodies or
antibodies / antitoxins not effective
• people / animals travel between countries / abroad
spreading infection
Jan 10 (H) Qu 6
• 6 (a) produces toxins / damage cells /
reproduce rapidly or reproduce in cells
• 6(b) any three from:
• TV crew immune / Indians not immune / Indians have
weak(er) immune system
• TV crew had / produced antibodies / Indians had no
antibodies or antibody production faster in TV crew
• TV crew had previous exposure to flu / had been
vaccinated or Indian tribe had no previous exposure to
flu / had not been vaccinated
• Indians caught disease from TV crew or TV crew were
carriers (of thevirus)