Infection and Response

• Pathogens that cause infectious diseases include viruses, bacteria, protists, and fungi
• Pathogens can infect plants or animals and spread through direct contact, water, or air
• Viruses:

  • Very small
  • Move into cells to make copies of themselves, leading to cell bursting and illness
• Bacteria:

  • Small
  • Multiply quickly through binary fission
  • Produce toxins that damage cells
• Protists:

  • Some are parasitic, using humans and animals as hosts
• Fungi:

  • Can be single-celled or have a body made of hyphae
  • Produce spores that can spread to other organisms
• Ways pathogens are spread:

  • Direct contact (e.g., kissing, touching contaminated surfaces)
  • By water (drinking or contact with dirty water)
  • By air (e.g., droplet infection when sneezing, coughing, or talking expels pathogens)
• Methods to reduce pathogen spread:

  • Improving hygiene (hand washing, using disinfectants)
  • Removing vectors (using pesticides, insecticides, and removing habitats)
  • Vaccination (injecting harmless pathogens to build immunity)
• Viral Diseases:

  • Viruses can enter all types of cells
  • Measles symptoms include fever, red skin rash, pneumonia, encephalitis, and blindness
  • Spread through droplet infection
  • Prevented by vaccinations
• Bacterial Diseases:

  • Salmonella food poisoning symptoms include fever, stomach cramps, vomiting, diarrhea
  • Spread through raw meat, eggs, unhygienic conditions
  • Prevented by vaccination, hygiene practices
• Fungal Diseases:

  • Rose black spot symptoms include purple or black spots on rose leaves
  • Spread through water or wind
  • Prevented by fungicides or removing affected leaves
• Protist Diseases:

  • Malaria symptoms include fevers and shaking
  • Spread by female Anopheles mosquito
  • Prevented by insecticide nets, eliminating stagnant water, antimalarial drugs
• Human Defence System:

  • Non-specific defense system prevents pathogens from entering the body
  • Skin, nose, trachea, bronchi, stomach act as barriers
  • Specific immune system uses white blood cells for defense mechanisms
• Vaccination:

  • Makes individuals immune to diseases before infection
  • Stimulates white blood cells to produce antibodies
  • Helps achieve herd immunity and prevent epidemics
• Antibiotics and Painkillers:

  • Antibiotics kill bacterial pathogens without harming body cells
  • Painkillers treat symptoms, not the cause
  • Antibiotics have reduced deaths from bacterial diseases
  • Advantages of vaccination: eradication of diseases, prevention of epidemics
  • Disadvantages: not always effective, rare bad reactions
• Bacteria are becoming resistant to antibiotics
• Mutations can occur during reproduction, resulting in certain bacteria no longer being killed by antibiotics
• When exposed to antibiotics, only the non-resistant bacteria die
• Resistant bacteria survive and reproduce, increasing the population of resistant bacteria
• This leads to previously effective antibiotics no longer working
• To prevent the development of resistant strains:

  • Stop overusing antibiotics to avoid unnecessary exposure
  • Finish courses of antibiotics to kill all bacteria
• Discovery and Development of Drugs:

  • Many drugs were initially discovered in plants and microorganisms
  • New drugs today are mainly synthesised by chemists
  • Drugs need to be tested for toxicity, efficacy, and dose using preclinical testing and clinical trials
• Monoclonal Antibodies:

  • Identical antibodies produced from the same immune cell
  • Used to target chemicals and cells in the body for various medical purposes
• Producing Monoclonal Antibodies:

  • Scientists obtain mice lymphocytes stimulated to produce a specific antibody
  • Combined with tumour cells to form a hybridoma
  • Hybridoma divides to produce clones that all produce the same antibody
  • Antibodies are collected and purified
• Uses of Monoclonal Antibodies:

  • In pregnancy tests
  • In laboratories to measure and monitor hormone or chemical levels
  • In research to find or identify certain molecules on a cell or tissue
  • In the treatment of diseases like cancer
• Advantages of using monoclonal antibodies:

  • Specific cell targeting without affecting healthy cells
  • Can be engineered to treat various conditions
• Disadvantages of using monoclonal antibodies:

  • Difficult to attach to drugs
  • Expensive to develop
• Plant Disease:

  • Plants can be affected by viral, bacterial, and fungal pathogens
  • Common signs of plant diseases include stunted growth, spots on leaves, areas of decay, abnormal growths, malformed stems or leaves, discolouration, and pests on leaves
• Ion deficiencies in plants:

  • Nitrate deficiency can stunt growth
  • Magnesium deficiency can cause chlorosis
• Plant Defence Responses:

  • Physical, chemical, and mechanical adaptations to prevent invasion of microorganisms
• Physical defences:

  • Tough waxy cuticle on leaves
  • Cellulose cell walls as a barrier into cells
  • Layers of dead cells around stems to stop pathogen entry
• Chemical defences:

  • Poisons and antibacterial compounds from plants to deter predators and kill bacteria
• Mechanical defences:

  • Thorns, hairs, and mimicry to deter animals and insects