• 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

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

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

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.

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

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.

• 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.

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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