infection and response


Pathogens are microorganisms such as viruses and bacteria that cause infectious diseases in animals and plants. They depend on their host to provide the conditions and nutrients that they need to grow and reproduce. They frequently produce toxins that damage tissues and make us feel ill. This section will explore how we can avoid diseases by reducing contact with them, as well as how the body uses barriers against pathogens. Once inside the body our immune system is triggered which is usually strong enough to destroy the pathogen and prevent disease. 

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name all 4 types of pathogens

  • bacteria
  • viruses
  • protists
  • fungi
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How do Bacteria and Viruses cause disease?

Bacteria and viruses reproduce rapidly inside the body.

Bacteria may produce poisons (TOXINS) that damage tissues and make us feel ill.

The spread of diseases can be reduced or prevented by:

• simple HYGIENE measures (break chain of infection, hand washing etc.)

• destroying VECTORS ( organisms that carry the disease)

• isolation of infected individuals (Quarantine)

• vaccination.

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what is a virus?

• not living cells

•  much smaller than bacteria and fungi

They are: a protein coat

• surrounding a strand of genetic material.

They: can only reproduce in other living cells

• only attack specific cells

• may attack plant, bacterial or animal cells

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how do viruses reproduce?

attaching itself to a specific host cell injecting its genetic material into the cell using the cell to make the components of new viruses causing the host cell to split open to release the viruses. (kinda like when a bug lays it eggs in another bug to hatch)

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name 3 bacterial diseases in humans?

  • sore throat
  • gonorrhoea
  • food poisoning
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what is bacteria?

Do NOT have a nucleus

Have a cell wall (not made of cellulose)

They are living and found in most places.  They are much smaller than plant and animal cells.

Most are harmless but others cause disease.

They attack the body or release toxins, making you ill.


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what are protists?

These can be any of a numerous EUKARYOTIC organisms : not fungi, plants, or animals and are chiefly unicellular or colonial. 

Malaria caused by the protist Plasmodium.

Spread via mosquitos: female sucks it up when she takes your blood

Cause recurring fever which can kill

Spread reduced by:

Stopping the mosquito biting:

Mosquito nets Long sleeves Insect repellant

Destroying the LARVAE

Drain ponds Use fish to eat them

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name the ways of spreading disease

  • air bourne
  • though dirty water
  • physical contact
  • contaminated food
  • passed on by other animals
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human lines of defence

1st line 

  • skin; cover organs
  • stomatch acid; kills bacteria
  • lysozymes; tears or saliva are antibacterial
  • hairs; act as a physical barier

2nd line

  • phagocytes; engulth pathogen, type of white blood cell

3rd line

  • antitoxins; neutralise what pathogens toxins
  • lymphocytes; second type of white blood cells, shape to fit antibody like lock and key
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plant defences


  • cellulose cell wall
  • tougth waxy cutical
  • layers of dead skin (bark on tree)


  • thorns
  • leave that droop or curl
  • mimi cry so as not to eat or lay eggs


  • antibacterial chemicals
  • produce poisons
  • make healthy cells die to stop spread
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what is herd immunity?

if a large population is immune to a pathogen, the spread of the pathogen is very much reduced


expensive, feel side effect, cause pain, allergies, stressful, may not always be effective.


less people get ill, protect those not vacsinated, go on holiday, irradicate disease, reduce strain on hospitals and its staff.

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