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Biology · Defence Against Disease

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Biology · AQA Paper 1

Defence Against Disease

Human Defence Systems

The skin, nose, airways and stomach stop most pathogens getting in. White blood cells destroy the rest.

  • Non-specific defence A defence that works in the same way against all pathogens, such as the skin.
  • Immune system The white blood cells that destroy pathogens inside the body.
  • Phagocytosis The engulfing and digestion of a pathogen by a white blood cell.
A person with labels pointing to the skin, nose, trachea and bronchi, and stomach as the body's non-specific defences.
Each of these barriers tries to stop pathogens getting in.

Non-specific defences and the immune system compared

  • Non-specific defences The same against every pathogen; The first line of defence; Skin, mucus, cilia and stomach acid
  • The immune system Antibodies fit one antigen only; Attacks pathogens that get in; Phagocytes, antibodies and antitoxins

Making the right antibodies

  • A pathogen enters Its surface carries antigens that are different from the body's own.
  • Lymphocytes respond A lymphocyte with a matching antibody starts to divide.
  • Antibodies are released The cells make large numbers of the antibody that fits that…
  • The pathogen is destroyed The antibodies stick to the pathogens, and phagocytes engulf them.

Vaccination

A vaccine contains dead or inactive pathogens, which trigger the production of antibodies without making you ill.

  • Vaccination Introducing a dead or inactive form of a pathogen into the body to stimulate the production of antibodies.
  • Vaccine The preparation containing dead or inactive pathogens that is used in vaccination.
  • Immune Protected against a disease because the body can make the right antibodies quickly.
Four steps showing a vaccine being given, antibodies being made, the real pathogen arriving later and being destroyed quickly by antibodies.
A vaccinated person responds quickly to the real pathogen, so they do not become ill.

The immune response after vaccination

  • Vaccination A small amount of dead or inactive pathogen is injected.
  • Antibodies are made The white blood cells recognise the antigens and make antibodies.
  • Memory cells Some white blood cells stay in the body.
  • Later infection The same pathogen enters the body.
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Biology · AQA Paper 1

Defence Against Disease continued

Antibiotics and Painkillers

Antibiotics kill bacteria. They do not kill viruses. Painkillers treat symptoms but do not kill pathogens.

  • Antibiotic A medicine, such as penicillin, that kills bacteria inside the body.
  • Penicillin The first antibiotic, discovered by Alexander Fleming.
  • Painkiller A medicine that reduces pain and other symptoms, but does not kill pathogens.
Four steps showing one resistant bacterium surviving an antibiotic, reproducing and forming a population of resistant bacteria.
Antibiotics kill the non-resistant bacteria, so the resistant ones survive and reproduce.

Antibiotics and painkillers compared

  • Antibiotics Kill bacteria inside the body; Cure bacterial disease; Specific to certain bacteria
  • Painkillers Reduce pain and other symptoms; Do not kill pathogens; Work for many illnesses

How a resistant strain arises

  • Variation Bacteria mutate, and by chance one has a gene that makes it…
  • The antibiotic is used It kills the non-resistant bacteria but not the resistant one.
  • Survival The resistant bacterium survives and reproduces rapidly, passing…
  • A resistant strain Soon most of the bacteria in the patient.

Discovery and Development of Drugs

A drug must be shown to be safe and to work before it is used on patients.

  • Toxicity How harmful a drug is to the body.
  • Efficacy How well a drug works to treat a disease.
  • Dose The amount of a drug given.
A five-stage pipeline showing discovery, preclinical testing, a safety trial with healthy volunteers, patient trials and peer review.
Every new drug goes through these stages before it is used.

Testing a new drug

  • Preclinical testing Done in a laboratory using cells and tissues.
  • Clinical trial: safety The drug is first given to healthy volunteers, at a very low dose.
  • Clinical trial: dose If it is safe, further trials with patients are carried out to…
  • Clinical trial: efficacy A larger group of patients is given the drug, to check that it works.