Quartz 4

Insecticides

2 min read

  • Substances used to kill insects
    • Insects may:
      • Destroy crop plant
      • Transmit diseases → e.g. dengue fever and malaria

One disadvantage of using insecticides → insecticides → may become ineffective → after some time.

  • Because → some insects become resistance to insecticides.
  • They pass the favourable genes to their offspring and over time → population of insects will rise again

Another disadvantage → insecticides may affect organisms rather than insects.

  • If insecticides → are carried by rainwater → into streams, rivers, lakes → they can accumulate in high concentrations in bodies of aquatic organisms such as fish

DDT(Dichlorodiphenyltrichloroethane) → insecticide → non-biodegradable

  • Cannot be broken down → by micro-organisms → like bacteria
  • Remains in soil or water for many years.

Since DDT → insoluble in water → it is not excreted.

  • It is stored in fatty tissues of organisms → that consume it

Since DDT → cannot be broken down → it accumulates in bodies of consumers

  • If consumers continue to eat food that contain DDT → concentration of DDT will increase in bodies
    • Known as bioaccumulation → accumulation of chemical substances such as pesticides → in an organism

Biomagnification or bioamplification → occurs → when toxins or insecticides → are passed from 1 trophic level to next with increasing concentration along the food chain.

Definition

Biomagnification → occurs when certain chemicals, e.g. insecticides → are passed along the food chain, increasing in concentration in the bodies of organisms along the trophic levels #BiologyDefinitions

Top consumers in food chain → can accumulate large amounts of DDT → From eating affected prey

  • Due to biomagnification → top consumers with high concentration of DDT → in bodies → may suffer → toxic effects

E.g. → events in Minamata, Japan → led to people being poisoned by mercury is an example of biomagnification

Sample

With reference to plankton and small fish, suggest how process of bioaccumulation takes place 1 When small fish consume plankton, mercury passes from plankton to small fish 2 Since mercury is insoluble in water, it is not excreted. 3 Instead, mercury is stored in the fatty tissues of small fish + Mercury cannot be broken down by small fish and hence accumulated in the bodies of small fish.

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