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Chemistry 2

also known as Acids and Bases

Table of Contents

Hey there! Please be advised if you’re an boi this doesn’t exactly match your textbook! I’ve tried to keep similar concepts together so if you can’t find something, feel free to use the textbook, or use that neat little search bar up the top there! Thanks!

Communicable Diseases on BBC Bitesize (AQA GCSE)

basically the better version of this


Disease can be sorted into two categories:

  • Infectious - caused by pathogens (e.g bacteria, viruses, fungi) and are contagious
  • Non-infectious - no pathogens and non-contagious

Classifying diseases

Infectious diseases

Pathogens are parasites that live in or on other organisms (the host) and have a harmful effect on their host. What bad guests! They can either me microscopic (invisible to the naked eye) or macroscopic (visible to the naked eye). Meet the pAtHoGeNs!

Type of pathogen Description Typical size Example of disease
Bacteria Single celled organisms with DNA outside of the nucleus 0.2-5μm Leprosy, throat infections, scarlet fever, HIV
Viruses DNA or RNA wrapped in protein, requires a host to reproduce 20-300nm AIDS, influenza, hepatitis, measles, salmonella
Protozoa Single celled organisms with DNA inside the nucleus 2-200μm Malaria, cryptospordium
Fungi One or more cells with cell walls and a nucleus, but no chloroplast 50μm –> much larger Ringworm, athlete’s foot

Transmission can occur through direct contact, water, air, food, or other organisms (vectors). The table from BBC Bitesize below outlines some examples.

Type Examples
Direct contact This can be sexual contact during intercourse or non-sexual contact, like shaking hands.
Water Dirty water can transmit many diseases, such as the cholera bacterium.
Air When a person who is infected by the common cold sneezes, they can spray thousands of tiny droplets containing virus particles to infect others.
Unhygienic food preparation Undercooked or reheated food can cause bacterial diseases like Escherichia coli which is a cause of food poisoning.
Vector Any organism that can spread a disease is called a vector. Many farmers think tuberculosis in their cattle can be spread by badgers.

There are also macroparasites and prions but this isn’t important for now.

Non-infectious diseases

Type of disease Description
Nutrition Overeating, undereating, unbalanced diet
Ageing Gradual breakdown of body tissues
Cancer Multiplication of body cells at an abnormal rate
Inherited disorders Passed on from family genes
Mental disorders Caused by chemical deficiencies, strees, trauma
Metabolic disorders Caused by chemical deficiencies
Environmental disorders Exposure to poisons, asbestos, fire, drugs, pollution

Most people die from lifestyle diseases such as cardiovascular diseases (stroke, heart attack) which is caused by obesity and lack of nutritione/exercise or lung cancer as a result of smoking.

Lines of Defence

Your body has many defences against pathogens. They can be either specific/non-specific. Specific defences involve targeted and tailored immunity of invading pathogens, while non-specific defences are applied to all threats equally.

First line of defence – Non-specific

The first line of defence are physical and chemical barriers that try to prevent entry of invading pathogens.

Physical barriers include:

  • skin
  • coughing
  • sneezing
  • hairs and eyelashes
  • cilia

Chemical barriers include:

  • saliva
  • tears
  • stomach acid
  • mucus

Second line of defence – Non-specific

If a pathogen evades the first line of defence, the second line of defence kicks in. At this point, an infection has occured.

  • Affected area becomes swollen and inflamed, while body temperature increases
  • More blood is directed to the area and blood vessels become permeable (porous - more leaky)
  • White blood cells including phagocytes move to the infected area
  • Phagocytes engulf and destroy pathogens

Third line of defence – Specific

If a pathogen evades the first and second lines of defence, then the third line of defence kicks in. It is specific immunity; which is targeted and tailored towards the type of pathogen. Any foreign particle that stimulates the production of antibodies (usually through an immune response) is an antigen.

  • Antigen enters body and lymphocytes (white blood cells) begin to divide. They split into specialised B lymphocytes and T lymphocytes (B cells and T cells respectively)
  • B cells produce plasma cells which produce antibodies that bind with particular antigens. The first time the body is exposed to a specific type of antigen is a trial and error phase which takes 10-17 for the right antibodies to be produced
  • T cells assist B cells to create an antibody and they do different jobs (e.g attack pathogens, attract/activate phagocytes, assist B cells with antibody production, etc)

Remember! Phagocytes are non-specific white blood cells, while lymphocytes are specific.

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