Infection and Response

The PiXL Club

• This resource is strictly for the use of member schools for as long as they remain me

• It may not be copied, sold nor transferred to a third party or used by the school after membership ceases.

• Until such time, it may be freely used within the member school.

• All opinions and contributions are those of the authors.

• The contents of this resource are not connected with nor endorsed by any other company, organisation, or institution.

• Website: www.pixl.org.uk

• The PiXL Club Ltd, Company number 07321607 ©

PiXL KnowIT! GCSE Biology AQA Topic – Infection and Response

Overview of Topics

• Communicable Diseases

  • Communicable (infectious) diseases

  • Viral diseases

  • Bacterial diseases

  • Fungal diseases

  • Protist diseases

• Human Defence Systems

• Vaccination

• Antibiotics and Painkillers

• Discovery and Development of Drugs

• Monoclonal Antibodies (Biology Higher Tier only)

  • Producing monoclonal antibodies

  • Uses of monoclonal antibodies

• Plant Disease (Biology only)

  • Detection & identification of plant diseases

  • Plant defence responses

Infection and Response Part 1

Infectious Diseases

• Pathogens: Microorganisms that cause infectious diseases, affecting both plants and animals. They can be spread through:

  • Direct contact (D)

  • Water (W)

  • Air (A)

• Types of Pathogens:

  • Bacteria

  • Viruses

  • Fungi

  • Protists

Viral Diseases

• Characteristics of Viruses:

  • May reproduce rapidly, invade host cells, and cause damage.

• Examples of Viral Diseases:

  • **Measles: **

  • Symptoms: Fever; red skin rash.

  • Can be fatal if complications occur.

  • Transmission: Spread by inhaling droplets from sneezes and coughs.

  • Control: Vaccinating young children.

  • HIV:

  • Initial symptoms: Flu-like illness.

  • Transmission: Spread through sexual contact or exchange of body fluids (e.g., sharing needles).

  • Without treatment, it attacks the immune system.

  • Late-stage HIV or AIDS occurs when the immune system can no longer combat infections.

  • Tobacco Mosaic Virus:

  • Affects plants, creating a distinct mosaic pattern on leaves.

  • Enters through damaged epidermis and affects photosynthesis.

  • Control: Remove infected leaves and destroy pests that caused damage.

Bacterial Diseases

• Characteristics of Bacteria:

  • May reproduce rapidly and produce toxins that damage tissues.

• Examples of Bacterial Diseases:

  • Salmonella:

  • Caused by bacteria in improperly prepared food.

  • Symptoms: Fever, abdominal cramps, diarrhoea, vomiting.

  • Control: Vaccination of poultry.

  • Gonorrhoea:

  • Sexually transmitted disease (STD).

  • Symptoms: Thick yellow/green discharge, pain during urination.

  • Control: Antibiotics; barrier contraception methods like condoms.

Fungal and Protist Diseases

• Example of a Fungal Disease:

  • Rose Black Spot:

  • Symptoms: Purple or black spots on leaves; leaves may turn yellow and drop off.

  • Transmission: Spores spread by wind/water.

  • Control: Remove infected leaves and spray with fungicide.

• Example of a Protist Disease:

  • Malaria:

  • Caused by a protist spread by mosquitoes.

  • Symptoms: Recurrent fever; can be fatal.

  • Control: Prevent mosquito breeding and use of mosquito nets.

Types of Diseases

Infection and Response Part 1 – QuestionIT

Questions for Understanding

1. Define a pathogen.

2. List four types of microorganisms that can act as pathogens.

3. Compare how bacteria and viruses act as pathogens (similarity & difference).

4. What do pathogens need from their host?

5. Complete the sentences:

   • HIV can be successfully controlled with ______ ___________ drugs.

   • If the immune system is badly damaged, then _____ may develop.

Answers to Questions

• 1. Definition of Pathogen: Micro-organisms that cause infectious disease in animals and plants.

• 2. Types of Microorganisms: Bacteria, Virus, Protist, Fungus.

• 3. Comparison Table:

  Pathogen	Similarity	Difference
  Bacteria	Reproduce rapidly inside the body	Produce toxins that damage tissues
  Virus	Reproduce rapidly inside the body	Live and reproduce inside cells causing cell damage

• 4. Needs from Host: Suitable conditions and nutrition for growth and reproduction.

• 5. Complete Sentences: HIV can be successfully controlled with antiretroviral drugs. If the immune system is badly damaged, then AIDS may develop.

Infection and Response Part 1 – Human Defence Systems

Overview of Human Defence

• Non-Specific Defences:

  • Nasal hairs, sticky mucus, and cilia filter out pathogens entering through the nostrils.

  • Stomach acid (pH 1) kills most ingested pathogens.

  • The respiratory system has mucus to trap dust/pathogens, with cilia moving mucus to be swallowed.

  • The skin acts as a waterproof barrier, and glands secrete oil that kills microbes.

• Immune System Function: Once a pathogen enters the body:

  • White Blood Cells are involved in identifying and destroying the pathogen.

  • Identification of Pathogens: White blood cells recognize pathogens by their specific surface proteins called antigens.

White Blood Cell Actions

1. Phagocytes engulf and digest pathogens through phagocytosis.

2. Lymphocytes identify antigens and produce specific antibodies to destroy pathogens. Subsequent infections are fought much quicker due to memory cells.

3. Antitoxins are released by white blood cells to neutralize toxins produced by bacteria.