Unit 4: Agriculture - Pests and Pesticides

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  • Pests and Pesticides
    • Weeds
      • Reduce crop yields by
        • Competing
        • Contaminating crop and spoiling taste
        • Providing food for other pests
      • Herbicides
        • Hormone herbicides - systematic (absorbed) and modify growth or development e.g. unrestricted growth so plant runs out of food reserves
        • Contact herbicides - damage cell membranes and leaf surfaces
    • Insects
      • Reduce crop yields by
        • Eat the crop
        • Spoil crop appearance
        • Spread diseases
      • Insecticides
        • Organochlorines e.g. DDT - overstimulates nerves causing death
          • Persistent and lipsoluble = bioaccuum and mag
        • Organophosphates e.g. malathion - prevent normal nerve function
          • Very toxic to mammals
        • Pyrethroids - overstimulates nerves
          • Toxic to fish but biodegradable
    • Micro-organisms
      • Antibiotics
        • Controls infections in sick animals
        • Prevent infections occuring
        • Reducing gut bacteria numbers to increase gross growth efficiency
        • Problems - can cause antibiotic resistant zoonoses
          • Zoonose - micro-organism that is carried by livestock and causes disease in humans


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