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6.2.2Unit 6: Practical Skills in Biology II

Pathogens: Routes of Entry — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 5 parts Lesson 8 of 48 Unit quiz

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Part 1 of 5Ways of Spreading

6.2.2 Pathogens: Routes of Entry
Vectors
  • Living organisms such as mosquitoes carry a pathogen from one host to another, as in malaria and yellow fever.
Inhalation
  • Droplets from coughs and sneezes are breathed in, spreading influenza, measles and tuberculosis.
Ingestion
  • Contaminated food or water carries pathogens into the digestive system, as in cholera and Salmonella poisoning.
Indirect contact
  • Objects such as towels, bedding and surfaces carry pathogens that are then transferred to the mouth, nose or eyes.
Mouth and nose
  • Food, drink and air all pass through the mouth and nose, so these are the commonest routes by which pathogens enter.

Part 2 of 5Contact and Inoculation

Contact and Inoculation
Direct contact
  • Skin or body fluids of an infected person touch a healthy person, for example in sexual transmission of HIV.
Inoculation
  • Pathogens enter through broken skin, giving a direct route into the blood, as with tetanus or rabies.
Needles
  • Sharing needles can transfer hepatitis B or HIV directly into the bloodstream.
Openings
  • Body openings such as the mouth, eyes and urinary tract provide easy entry points.

Part 3 of 5Physical and Chemical Barriers

Skin
  • Skin is a physical barrier, and if it is damaged the exposed tissue becomes open to infection.
Blood clotting
  • Clotting seals wounds and restricts entry, although some pathogens enter before the clot forms.
Stomach acid
  • Hydrochloric acid in gastric juice kills many pathogens that are taken in with food and drink.
Lysozyme
  • This enzyme in tears, saliva and mucus damages bacterial cell walls, causing the bacteria to burst.
Mucus
  • Mucus in the airways traps microorganisms, and cilia sweep the trapped material away from the lungs.

Part 4 of 5Competition and Control

The body therefore has several layers of defence before the immune system itself needs to act.

1
Harmless microorganisms living on the skin and in the gut are called flora.
2
They compete with pathogens for nutrients and space, which limits the numbers of pathogens.
3
If the barriers fail, a pathogen enters the body and the immune response begins.
4
The immune system then responds, first with non-specific defences and then with the specific response.
5
Good hygiene and clean food and water reduce the opportunities for pathogens to enter.

Part 5 of 5Exam Checklist & Tips

6.2.2 – Key Points for the Exam

  • Vector A living organism that carries a pathogen between hosts.
  • Inoculation Entry of a pathogen through a break in the skin.
  • Lysozyme An enzyme that breaks down bacterial cell walls.
  • Flora Harmless microorganisms that live on the skin and in the gut.
  • Direct contact Transfer of a pathogen when the body of an infected person touches another person.

Common Mistakes

  • Saying the stomach destroys all pathogens; some survive and reach the intestines.
  • Using direct and indirect contact as if they were the same; indirect contact involves an object.
  • Describing lysozyme as killing viruses, when it acts on bacterial cell walls.
  • Forgetting that blood clotting takes time, so some pathogens may enter first.

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