Infection

• Pathogens: disease causing microorganisms
• VIRUS

  How it infects:

  • moves into cells and uses it to make copies of itself until cells burst, causing symptoms
• BACTERIA

  How it infects:

  • multiplies fast through binary fission, produces toxins that damage cells and cause symptoms
• PROTISTS

  How it infects:

  • parasitic: uses humans and animals as hosts
• FUNGI

  How it infects:

  • produces spores which can spread to other organisms
• Fungi are either single celled or multi cellular
• Pathogen spreading

  Direct contact: skin to skin, contact with bodily fluids

  Indirect contact: droplets (sneezing), through the air (breathing)
• General pathogen prevention

  • vaccination
  • killing vectors
  • improved hygiene
  • isolation from infected
• VIRAL DISEASES

  Measles:

  • SYMPTOMS: fever, skin rash
  • SPREAD: droplets
  • PREVENTION: vaccination for young children

  HIV:

  • SYMPTOMS: flu like, leads to AIDS
  • SPREAD: sexual contact, exchange of fluids
  • PREVENTION: condoms, not sharing needles

  Tobacco Mosaic Virus:

  • SYMPTOMS: discoloured leaves reduces area for photosynthesis
  • SPREAD: contact from diseased
  • PREVENTION: field hygiene, pest control
• BACTERIAL DISEASES

  Salmonella:

  • SYMPTOMS: fever, vomiting
  • SPREAD: digested from raw meat
  • PREVENTION: cook food throughly

  Gonorrhoea:

  • SYMPTOMS: thick discharge from penis, pain when urinating
  • SPREAD: sexual contact
  • PREVENTION: condoms
• FUNGAL DISEASES

  Rose black spot:

  SYMPTOMS: purple or black spots on leaves reduces area for photosynthesis

  SPREAD: spores spread from wind or rain

  PREVENTION: destroying infected leaves
• PROTIST DISEASES

  Malaria:

  • SYMPTOMS: fever, shaking when protists burst blood cells
  • SPREAD: female mosquito acts as vector, punctures skin to feed on blood, protists enter blood stream via saliva
  • PREVENTION: remove stagnant water to prevent vector breeding, insecticide coated nets while sleeping
• HUMAN DEFENCE SYSTEM

  Prevention:

  • SKIN: acts as physical barrier
  • NOSE: hairs and mucus prevent pathogens entering lungs
  • TRACHEA + BRONCHI: cilia wafts mucus upwards so it doesn’t get swallowed
  • Stomach: hydrochloric acid kills pathogens in mucus, food or drink
• HUMAN DEFENCE SYSTEM

  Destruction:

  • PHAGOCYTOSIS: white blood cells engulf and consume pathogens so they can’t make you feel ill
  • ANTIBODIES: antibody binds to complimentary antigen on the pathogen, acts as a signal for white blood cells to come and destroy the pathogen (if infected again, antibodies produce at a faster rate so person doesn’t get symptoms, they are immune)
  • ANTITOXINS: neutralise toxins released by pathogen by binding to them
• Vaccination: the protection of a person from a disease before infection
• Herd immunity: immunising lots of the population to reduce spread as there’s less people to catch it from
• VACCINATION

  • harmless form of pathogen is injected
  • white blood cells produce antibodies specific to antigens

  ✅ eradicated diseases like smallpox

  ✅ reduces occurrences of diseases

  ❌ not always effective in providing immunity

  ❌ can have side effects
• Antibiotics kill pathogens inside the body without damaging body cells
• Antibiotics can’t attack viruses as viruses use body cells to reproduce, virus-attacking drug would attack body tissue
• Painkillers treat symptoms, they don’t eradicate the disease
• Resistance to antibiotics

  • mutation occurs, making antibiotics useless
  • resistant bacteria reproduces

  Reducing resistance:

  • avoid overusing antibiotic (it exposes bacteria to antibiotic)
  • finish antibiotic course to kill all bacteria
• Discovery of drugs

  In plants :

  • aspirin is a pain killer from willow
  • digitalis treats heart problems from foxgloves

  In microorganisms:

  • Alexander Fleming was growing bacteria on plates, found penicillium mould on plates with rings indicating no bacteria
• Development of drugs

  3 factors: efficacy, toxicity, dosage

  Preclinical testing: testing on cells, tissues, live animals

  Clinical testing: testing on healthy people to discover side effects (maximum dosage), test on sick people (optimum dosage)

  • large scale double blind trials: 1 group receive drug, 1 group receive placebo to remove physiological bias where you might report side effects which aren’t related
• Monoclonal antibodies: identical antibodies made in a lab
• Monoclonal antibody production

  1. inject mouse with antigen we want antibodies to bind to
  2. immune response leads to mouse lymphocytes which fuse with tumour cell to make a hybriddoma cell
  3. tumour cell helps hydridoma cell divide rapidly with the antibodies needed
  4. antibodies are collected and purified
• Pregnancy tests (use hormone called hCG which is present in women’s urine)


  1. woman urinates on section 1, if hCG is present it binds to mobile antibodies (blue dye travels showing a positive result)
  2. antibodies and hCG travels to section 2, free to move hCG binds to stationary antibodies to show the test worked
• Monoclonal antibodies

  ✅ healthy cells aren’t attacked

  ✅ can be engineered to treat many conditions

  ❌ expensive

  ❌ difficult to attach antibodies to drugs
• Why do plants require nitrates

  To make proteins
• Why do plants require magnesium?

  To make chlorophyll
• What is a symptom of nitrate deficiency in a plant?


  Stunted growth
• What is the main symptom of magnesium deficiency for a plant?

  Chlorosis (yellow leaves due to lack of chlorophyll)
• three ways in which plant diseases can be identified

  • Use testing kits that contain monoclonal antibodies
  • Test the DNA of the pathogens
  • Use trial and error to test different treatments