Infection & response

• Pathogen

  -microorganisms that causes disease

  viruses e.g HIV or TMV

  bacteria e.g salmonella or agrobacterium

  fungi e.g athletes foot or rose black spot

  protists e.g malaria or downy mildew
• Transmission of diseases

  Direct contact = sexual or non-sexual e.g hand shake

  water = dirty water can contain microorganisms e.g cholera

  air = droplets travel when someone sneezes or coughs

  food = unhygienic preparation or reheated food can cause bacteria

  vector = organism that spreads disease e.g mosquito and malaria
• Viral disease

  -not alive and can survive outside of host for long time

  -infect host cells to replicate and then kill cell and repeat

  -cannot be treated with antibiotics

  e.g TMV = chloroplast infected turning white/yellow so no photosynthesis occurs

  HIV = transmitted via body fluids (unsafe sex or sharing needles) get flu like symptoms

  AIDS = caused by HIV and attacks immune syste, no cure but can get antiviral drugs to slow development
• Bacterial disease

  -not all bacteria is a pathogen but many are harmful

  e.g gonorrhoea = sexually transmitted, get yellow/green discharge treated with antibiotics if untreated leads to infertility

  salmonella = genus of bacteria from under cooked foods and unhygienic kitchens, get cramps vomiting + diarrhoea
• Protist disease

  -eukaryotic microorganisms

  e.g malaria = spread by mosquitos (vector) that carry a protist, suck blood and infect the person, get fever, chills, headaches etc, no vaccination but antimalarial drug +

  prevent with nets + repellent
• Fungal disease

  -not all cause disease like yeast is used for bread etc

  -eukaryotic

  -treated with anti-fungal medication

  e.g athletes foot = rash caused by a fungus causing dry red flaky or whit wet cracked skin, transmitted by direct contact

  rose black spot = infects rose leaves turning them black/purple and cause them to drop off, less photosynthesis so growth is reduced, transmitted by direct contact air or water, treat with fungicides or removing plants
• Human defences

  Skin = stops pathogens entering, if cut heals itself, physical barrier

  eyes = tears which have enzymes, chemical barrier

  nose = hairs act as physical barrier and mucus traps pathogens stopping them entering lungs

  trachea + bronchi = cilia hairs waft and move mucus towards throat and down to stomach

  stomach = hydrochloric acid kills pathogens, chemical barrier
• Vaccinations

  -allow dead or inert forms of the disease into the body so antibodies can be produced

  -this targets the antigens for that disease so phagocytosis can occur

  -primary infection antibodies slowly increase the gradually decrease

  -secondary infection the response is quicker which prevents infection
• Herd immunity

  -after vaccinations ppl can be immune to specific disease

  -if majority of ppl are immune Then the few who are unvaccinated have lower chance of coming into contact with the disease = herd immunity
• Antibiotics

  -slow down or stop growth of bacteria

  -E.g penicillin cure disease by killing bacteria cells not host cells

  -only kill bacterial not viral diseases
• Pain killers

  -chemicals that relieve symptoms but don’t kill the pathogen

  e.g paracetamol and aspirin
• antiviral Drugs

  -viral diseases can’t be treat with antibiotics

  -antiviral drugs are difficult to develop and need to be generated regularly

  -can damage host cells

  -only slow down viral development
• Antibiotic resistance

  -common antibiotics become less effective due to overuse, not completing full prescription and use in farming

  -effectiveness is reduced and resistance increases
• Reducing antibiotic resistance

  -only take when necessary

  -treat specific bacteria with specific antibiotics

  -high hospital hygiene e.g regular hand washing

  -isolate patients that have built up resistance
• New drugs

  -developed all the time

  -must be tested to ensure safety and they work

  -plants like willow bark = aspirin and fox gloves = digitalis and other organisms like penicillin mould = penicillin
• Testing new drugs

  -test for safety, effectiveness and dosage

  three stages :

  1 - preclinical - tested with computer and skin cells grown in labs to check for side effects and efficiency

  2 - tested on animals with different amounts and monitoring for side effects

  3 -clinical trail- human trials on healthy volunteers then once certain it’s safe it’s moved to patients with illness in low doses, if working dose increased until optimum found
• Clinical trial

  -involve real patients

  -patients in two groups and have a doctor

  -one group receives a fake drug of sugar called placebo

  -both group and doctor don’t know which they have so it’s a double blind trial (no bias)

  -results are published in medical journal and peer reviewed by scientists preventing false claims
• Monoclonal antibodies

  -are identical copy of one type of antibody

  -formed by injecting a mouse with antigen, mouse produces naturally lymphocytes making antibodies

  -then remove the spleen cells where produced

  -they are fused with cancerous white blood cell (myeloma) to form hybridoma cells

  -these cells divide and produce lots of monoclonal antibodies
• Uses of monoclonal antibodies

  Pregnancy tests - monoclonal antibodies designed to bind to hormone HCG in urine of pregnant women, when urine added onto stick it will wash down with antibodies and if HCG is present it binds to them and the fixed antibodies on test strip, this will form a coloured line

  cancer diagnosis/treatment - binds to cancer cells and clumps to identify where tumour is, can carry drugs to tumour + encourage immune system to attack tumour
• Benefits & limits

  +quick to produce

  +treat a d test for conditions

  -expensive

  -ethical issue
• Plant defences (physical)


  -thick bark is layer of dead cells

  -cellulose acts as another defence

  -leaves have waxy cuticles
• Plant defences (chemical)

  -antibacterial chemicals in plants like mint & witch hazel

  -sting nettles with poison prevent being eaten
• Plant defences (mechanical)

  -thorns and hairs to prevent being eaten

  -drooping leaves when creature lands on it makes it difficult to feed

  -mimicry of other plants and features