Detailed_Notes_diseses

AQA Biology GCSE Topic 3: Infection and Response

3.1 Communicable Diseases

3.1.1 Pathogens

• Definition: Pathogens are microorganisms that cause diseases, including:

  • Viruses

  • Bacteria

  • Protists

  • Fungi

• Transmission:

  • Direct Contact: Examples include kissing, skin contact, and contaminated surfaces.

  • Waterborne: Contaminated drinking water or surface contact.

  • Airborne: Pathogens spread in droplets through coughing or sneezing.

3.1.2 Viral Diseases

1. Viruses Overview

   • Very small microorganisms that infiltrate host cells, replicate, and lead to cell damage.

2. Examples:

   • Measles:

     • Symptoms: Fever and red rash.

     • Transmission: Droplet infection.

     • Prevention: Vaccination.

   • HIV:

     • Symptoms: Initially flu-like, leads to AIDS.

     • Transmission: Bodily fluids through sexual contact.

     • Prevention: Use of condoms, antiretroviral drugs, and breastfeeding considerations.

   • Tobacco Mosaic Virus:

     • Symptoms: Leaf discoloration affecting photosynthesis.

     • Transmission: Contact between infected and healthy plants.

     • Prevention: Field hygiene and resistant strains.

3.1.3 Bacterial Diseases

• Overview: Increasing bacterial resistance to antibiotics.

1. Salmonella:

   • Symptoms: Fever, cramps, vomiting, diarrhea.

   • Transmission: Raw meat and eggs, poor hygiene.

   • Prevention: Vaccination, good hygiene practices.

2. Gonorrhea:

   • Symptoms: Discharge and pain during urination.

   • Transmission: Unprotected sex.

   • Prevention: Contraceptives and antibiotics.

3.1.4 Fungal Diseases

• Rose Black Spot:

  • Symptoms: Purple/black spots on leaves, yellowing, early leaf drop.

  • Transmission: Spores spread via rain or wind.

  • Prevention: Fungicides and remove affected leaves.

3.1.5 Protist Diseases

• Malaria:

  • Symptoms: Fever, shaking.

  • Transmission: Female Anopheles mosquito.

  • Prevention: Insecticide nets, eliminating stagnant water, and antimalarial drugs.

3.1.6 Human Defence System

• Non-Specific Defences:

  1. Skin: Physical barrier, antimicrobial secretions.

  2. Nose: Hairs and mucus trap pathogens.

  3. Trachea/Bronchi: Mucus traps pathogens; cilia waft pathogens out.

  4. Stomach: Hydrochloric acid kills pathogens.

• Specific Immune System:

  • White Blood Cells: Fight infection via:

    1. Phagocytosis: Engulfing pathogens.

    2. Antibody Production: Bind to antigens of pathogens, leading to clumping for easier identification.

    3. Antitoxins: Neutralize toxins.

3.1.7 Vaccination

• Overview: Process of creating immunity before infection.

  • Herd Immunity: Many vaccinated individuals protect the wider population.

• Mechanism: Involves dead/inactivated pathogens to stimulate antibody production.

• Pros/Cons:

  • Advantages: Disease eradication and prevention of outbreaks.

  • Disadvantages: Not always effective and potential for adverse reactions.

3.1.8 Antibiotics and Painkillers

• Antibiotics: Target bacterial infections without harming body cells; ineffective against viruses.

  • Function: Kill bacteria and decrease bacterial disease mortality.

  • Examples: Penicillin.

• Painkillers: Alleviate symptoms but do not eliminate pathogens.

3.1.9 Discovery and Development of Drugs

• Origin: Many drugs derived from plants or microorganisms.

• Testing: Through preclinical and clinical testing.

• Plant-Derived Drugs:

  • Examples: Aspirin from willow, digitalis from foxgloves.

• Microbial-Derived Drugs:

  • Penicillin: Discovered by Alexander Fleming; killed bacteria near mould.

3.2 Monoclonal Antibodies (Biology Only)

3.2.1 Producing Monoclonal Antibodies

• Process:

  1. Mice lymphocytes stimulated to produce specific antibodies.

  2. Fusion with tumour cells to create hybridoma.

  3. Cloning hybridoma to produce identical antibodies.

3.2.2 Uses of Monoclonal Antibodies

1. Pregnancy Tests: Detect hCG in urine.

2. Laboratory Measurement: Hormone/chemical levels in blood.

3. Research: Identify specific molecules on cells.

4. Cancer Treatment: Targeting tumor markers with antibodies to enhance immune response.

3.3 Plant Disease (Biology Only)

3.3.1 Detection and Identification

• Symptoms of Plant Diseases:

  • Stunted growth, spots, discoloration, abnormal growths.

• Causes: Pathogens (viral, bacterial, fungal) and nutrient deficiencies.

3.3.2 Plant Defence Responses

• Physical Defences: Thick cuticles and cellulose walls.

• Chemical Defences: Poisons and antibacterial compounds.

• Mechanical Defences: Thorns, drooping leaves, and mimicry.