Infection and Response- Biology Paper 1

• Pathogens

  Microorganisms that cause infectious disease, including viruses, bacteria, protists and fungi
• Viruses


  • Very small
  • Move into cells and use the biochemistry to make many copies of itself
  • This leads to the cell bursting and releasing all of the copies into the bloodstream
  • The damage and destruction of the cells makes the individual feel ill
• Bacteria


  • Small
  • Multiply very quickly through dividing by a process called binary fission
  • Produce toxins that can damage cells
• Protists


  • Some are parasitic, meaning they use humans and animals as their hosts (live on and inside, causing damage)
• Fungi


  • Can be single celled or have a body made of hyphae (thread-like structures)
  • Can produce spores which can be spread to other organisms
• Ways pathogens are spread

  • Direct contact (touching contaminated surfaces, kissing, contact with bodily fluids, microorganisms from faeces, infected plant material)
  • By water (drinking or coming into contact with dirty water)
  • By air (pathogens carried in droplets from sneezing, coughing or talking)
• Ways to reduce the spread of disease

  • Improving hygiene (hand washing, using disinfectants, isolating raw meat, using tissues and handkerchiefs when sneezing)
  • Reducing contact with infected individuals
  • Removing vectors (using pesticides or insecticides and removing their habitat)
  • Vaccination
• Vaccination


  Injecting a small amount of a harmless pathogen into an individual's body, so they can become immune to it and not get infected
• Herd immunity


  When a large proportion of the population is vaccinated, the spread of the pathogen is reduced as there are less people to catch the disease from
• Measles


  • Symptoms: Fever and red skin rash, can lead to other problems such as pneumonia, encephalitis and blindness
  • Spread by droplet infection
  • Prevented by vaccinations for young children
• HIV


  • Symptoms: Initially flu-like, then virus attacks the immune system leading to AIDS
  • Spread by sexual contact or exchange of bodily fluids
  • Prevented by using condoms, not sharing needles, screening blood, and mothers with HIV bottle-feeding instead of breastfeeding
  • Treated with antiretroviral drugs
• Tobacco mosaic virus

  • Symptoms: Discolouration of leaves, affected part cannot photosynthesise resulting in reduced yield
  • Spread by contact between diseased and healthy plants, and by insects
  • Prevented by good field hygiene, pest control, and growing TMV-resistant strains
• Salmonella food poisoning

  • Symptoms: Fever, stomach cramps, vomiting, diarrhoea
  • Spread through raw meat, eggs, and unhygienic conditions
  • Prevented by vaccinating poultry, keeping raw and cooked food separate, and cooking food thoroughly
• Gonorrhoea


  • Symptoms: Thick yellow/green discharge, pain when urinating
  • Spread through unprotected sexual contact
  • Prevented by using contraception and antibiotics (though resistant strains are developing)
• Rose black spot


  • Symptoms: Purple/black spots on leaves, reduces photosynthesis, leaves turn yellow and drop early
  • Spread by water (rain) or wind
  • Prevented by using fungicides or stripping affected leaves
• Malaria


  • Symptoms: Fevers and shaking
  • Spread by female Anopheles mosquito, which acts as a vector
  • Prevented by using insecticide-treated nets, removing stagnant water, and taking antimalarial drugs
• Non-specific defence system

  • Skin (physical barrier, antimicrobial secretions, skin flora)
  • Nose (hairs and mucus to prevent particles entering lungs)
  • Trachea and bronchi (mucus to trap pathogens, cilia to waft mucus upwards)
  • Stomach (hydrochloric acid to kill pathogens)
• Specific immune system

  • Phagocytosis (white blood cells engulfing and consuming pathogens)
  • Producing antibodies (bind to pathogen antigens)
  • Producing antitoxins (neutralise pathogen toxins)
• Antibiotics


  Medicines that kill bacterial pathogens inside the body, without damaging body cells
• Painkillers


  Only treat the symptoms of a disease, rather than the cause
• Antibiotics cannot kill viruses as they use body cells to reproduce, meaning any drugs that target them would affect body tissue too
• The great concern is that bacteria are becoming resistant to antibiotics
• Ways to prevent antibiotic resistance

  • Stop overusing antibiotics (unnecessarily exposing bacteria)
  • Finish courses of antibiotics to kill all bacteria
• Epidemics (lots of cases in an area) can be prevented through herd immunity
• Bad reactions (such as fevers) can occur in response to vaccines (although very rare)
• Mutations can occur during reproduction resulting in certain bacteria no longer being killed by antibiotics


  1. When these bacteria are exposed to antibiotics, only the non-resistant one die

  2. The resistant bacteria survive and reproduce, meaning the population of resistant bacteria increases

  3. This means that antibiotics that were previously effective no longer work
• To prevent the development of these resistant strains

  • Stop overusing antibiotics- this unnecessarily exposes bacteria to the antibiotics
  • Finishing courses of antibiotics to kill all of the bacteria
• Toxicity

  How poisonous a drug is
• Efficacy


  How well a drug carries out its role
• Preclinical testing


  Using cells, tissues and live animals to test new drugs
• Clinical trials


  Using volunteers and patients to test new drugs
• New drugs today are mainly synthesised by chemists
• Any new drugs being developed need to be tested to ensure they are safe and effective
• Clinical testing

  1. First tested on healthy volunteers with a low dose to ensure there are no harmful side effects

  2. The drugs are then tested on patients to find the most effective dose

  3. To test how well it works, patients are split into two groups with one group receiving the drug and one receiving a placebo (appears to look like the drug but has no active ingredient so no effect) so the effect of the new drug can be observed
• Single-blind


  Only the doctor knows whether the patient is receiving the drug
• Double blind


  Neither the patient or doctor knows whether they are receiving the drug, removing any biases the doctor may have when they are recording the results
• The results then need to be peer reviewed by other scientists to check for repeatability
• Tumour markers

  Antigens on the cell membranes of cancer cells, not found on normal body cells
• The plant diseases that need to be learnt are tobacco mosaic virus (viral disease), black spot (fungal disease) and aphids as insects
• Nitrate deficiency


  Can stunt growth as nitrates in the soil convert sugars made in photosynthesis into proteins needed for growth