Life cycle of a virus

  • They can survive outside a host for long periods of time
  • They infect a suitable host cell 
  • They replicate themselves thousands of times 
  • They copy their genetic material (DNA or RNA) and protein coats
  • This often causes the host cell to burst 
  • Other cells can then be infected 
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Differences between phagocytes and lymphocytes

  • Phagocytes surround any pathogens in your blood and engulf them 
  • Enzymes inside the phagocytes then breakdown the pathogen 
  • lymphocytes recognise proteins on the surface of pathogens called antigens
  • they then produce antibodies which make pathogens stick together 
  • lymphocytes also produce antitoxins to neutralise the effects of toxins produced by pathogens 
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How pathogens can be transmitted

  • Direct contact which can be sexual or non-sexual 
  • Dirty water can transmit many diseases such as the cholera bacterium 
  • When a person who is infected by the common cold sneezes they can spray thousands of tiny droplets containing virus particles to infect others 
  • undercooked or reheated food can cause diseases like Escherichia coli which is a cause of food poisoning 
  • Via another animal called a vector 
  • Additional marks for correct pathogens and disease 
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Effects of viruses on plants

  • The tobacco mosaic virus infects tobacco and other closely related species 
  • It infects the chloroplasts of plant leaves 
  • It changes their colour from green to yellow or white in a mosaic pattern 
  • It can also make leaves crinkled or curled up - this reduces the plant’s ability to photosynthesise, which reduces the crop yield of farmers 
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Effects of viruses on animals

  • HIV stands for human immunodeficiency virus 
  • It is transmitted by body fluids, often during unprotected sex and injecting drugs using dirty needles 
  • Immediately after infection, infected people often suffer mild flu-like symptoms 
  • AIDS stands for acquired immune deficiency syndrome 
  • Months or years after infection the HIV virus becomes active and HIV turns into AIDS
  • it starts to attack the patient’s immune system 
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