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AS/A-level Biology - Communicable Disease

Communicable Disease

· Communicable disease,Pathogens,A-level Biology,as level biology,microorganisms

Pathogen

  • A microorganism that causes disease.

When it comes to AS/A-level Biology, do you remember which microorganisms can cause infectious diseases? 🤔

1. Bacteria

  • They belong to the kingdom prokaryotae.
  • They are smaller than Eukaryote cells and reproduce rapidly.
  • Their presence causes harm by damaging cells and releasing waste products/toxins.
  • In plants, they often live in the vascular tissues
  • E.g. Tuberculosis and ring rot
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2. Fungi

  • Common fungal infections are where the fungi lives in the skin of an animal and its hyphae which forms a mycelium grows under the skin surface.
  • The fungus can send out specialised reproductive hyphae which grow out of the skin surface to release spores.
  • The hyphae may release extracellular enzymes called cellulases to digest the surrounding host tissue.
  • E.g. Black sigatoka and athlete’s foot
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3. Virus

  • Viruses invade cells and take over the genetic machinery and other organelles of the cell.
  • They reproduce by causing the host cell to replicate the virus and when the host cell eventually burst the many new viruses are released to infect healthy cells.
  • E.g. Influenza and Tobacco mosaic virus
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4. Protoctista

  • Protoctista usually cause harm by entering the host cells and feeding on the contents as they grow.
  • The malarial parasite plasmodium has immature forms that feed on haemoglobin inside red blood cells and inhibits the organisms ability to transport oxygen around in the blood properly.
  •  This slowly prevents the tissue cells from respiring aerobically.
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Lifecycle of a pathogen

  • Travelling from one host to another.
  • Entering the hosts tissues.
  • Reproducing.
  • Leaving the hosts tissues.

Direct Transmission

Means of transmission

  • Direct physical contact such as touching a person who is infected or touching contaminated surfaces including soil that harbour pathogens.
  • E.g. HIV, bacterial meningitis, athletes foot and ring worm
     
  • Faecal – oral transmission, usually by eating/drinking water contaminated by the pathogen.
  • E.g. cholera
     
  • Droplet infection – pathogen is carried by tiny airborne droplets.
  • E.g. tuberculosis and influenza
     
  • Transmission by spores which are a resistant stage of the pathogen – these can be carried in the air or reside of surfaces.
  • E.g. anthrax and tetanus

Factors that affect transmission

Direct physical contact

  • Hygiene – wash hands regularly.
  • Keeping surfaces clean.
  • Cleaning and disinfecting cuts.
  • Sterilising surgical equipment.
  • Using condoms during intercourse.

Faecal – oral transmission

  • Treatment of waste water.
  • Treatment of drinking water.
  • Thorough washing of all fresh food.Careful food preparation and cooking.

Droplet infection

  • Catch it – bin it – kill it.
  • Cover your mouth when coughing or sneezing.
  • Use a tissue and dispose of it correctly.

Transmission by spores

  • Use of a mask.
  • Washing skin after contact with soil and/or contaminated surfaces.
  • Overcrowding, poor ventilation, poor health, poor diets, homelessness and living and working with people who have migrated from areas where disease is more common, all may affect the likelihood of catching a disease.

Indirect Transmission

  • Some pathogens, like the protoctista plasmodium that causes malaria, use vectors for transmission.
  • Indirect transmission of plant pathogen occurs as a result of insect attack.
  • The fungus that causes Dutch elm disease is carried by the beetle Scolytus multistriatus.
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References:

1. https://www.sanitized.com/zh/viruses-and-bacteria-a-brief-explanation-of-the-differences/

2. https://www.healtheuropa.eu/fungi-a-kingdom-to-address-the-antimicrobial-resistance-problem/95774/

3. https://link.springer.com/chapter/10.1007/978-3-030-02318-8_4

That's the end of the topic!

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Drafted by Bonnie (Biology)

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