KEEPING HEALTHYHow 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% allow

stopped in 1995

• 2(b)(ii) • (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 onlyExplain 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 anti-biotics

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)