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Bacteria are larger than viruses but still much smaller than cells. They divide using binary fission, which is similar to mitosis in that bacteria make many copies of themselves. Bacteria make you feel ill by releasing toxins. Bacteria can also use their surface receptors to gain entry into cells to use as a place to replicate in number.

When bacteria replicate (using binary fission) they grow in number exponentially, which means that their numbers double with each division (2,4,8,16,32...etc).

The primary defence system:
A non-specific set of defenses set up to kill pathogens (foreign dangerous particles such as viruses or bacteria).

 

  • Skin (slightly acidic, low pH kills pathogens, also physical barrier between internals and outside)

  • Ciliated epithelial cells and mucus (work together to trap pathogens in mucus, then waft them out of the lungs and into the stomach)

  • Stomach (highly acidic hydrochloric acid, low pH kills pathogens (enzymes denature-bonus point!)

The specific, long-term defence system:
A set of defenses set up to kill pathogens (foreign dangerous particles such as viruses or bacteria), comprising of white blood cells, antibodies and memory cells.

 

  • Antibodies (proteins which bind to toxins and neutralise them. Antibodies also bind to antigens on pathogens, marking them as foreign material to be destroyed)

  • White blood cells (produce the antibodies after destroying infected cells by phagocytosis. Also produce antitoxins)

  • Memory cells (remain in the body for many years providing immunological memory)

VS

Bacteria can develop resistance through the process of mutation, which is random within a population of bacteria, giving rise to variation.

Natural selection means that those with mutations that give them a selective advantage (gene resistant to dugs) then they are more likely to survive and reproduce, passing on the favourable allele.

Resistance

Phagocytosis:
Where a white blood cell engulfs and consumes either a virus or bacteria, destroying it using enzymes. Phagocyte means 'large eater'.

 

Pathogen
 

White Blood Cell

Viruses are neither living nor dead. They need a host cell to replicate inside of. Viruses inject their RNA into the host cell, which then turns to DNA. This DNA is then integrated into the host cell genome. The cell is what makes the many new virus particles through transcription and translation of the virus DNA.

The proteins coded for include: enzymes (to make the viral DNA and integrate it into the cell), receptors on the virus surface (which allow it to enter the cell) and parts of the capsid (which helps to deliver the viral RNA to the nucleus).

Fungi produce many billions of spores which are carried in the wind and allow it to replicate. They also produce hyphae (long cell body-like structures) and can be unicellular or multicellular.

Spread of disease:

Vaccination:

Antibiotics:

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