1.5 Food Production

• Why has there been a demand for higher food yield in recent years?

  There has been an increase in the human population.
• Why do farmers use fertilisers?

  Fertilisers provide chemicals such as nitrates. By increasing nitrate content of the soil they can increase crop yield.
• Why do farmers use pesticides?

  Plants and animals that reduce plant yield can be killed by pesticides.
• What happens to the nitrates that are dissolved in soil water?

  1 - absorbed by plants.

  2 - plants use nitrates to make amino acids

  3 - plants use amino acids to make plant proteins
• What is the cause of algal blooms?


  Fertilisers leach into fresh water, adding extra unwanted nitrates. This will increase algal populations which can cause algal blooms.
• Why do algal blooms kill aquatic plants?

  They reduce light levels.
• Why do algal blooms cause an increase in the number of bacteria in fresh water?

  Algal blooms kill aquatic plants. The dead aquatic plants and the algae become food for decomposing bacteria, which allows them to increase in number.
• Following an algal bloom there is an increased number of decomposing bacteria in the water. Name a negative consequence of having more bacteria in the water.

  The bacteria use up oxygen when they respire, reducing oxygen availability for other organisms.
• What are some problems associated with using pesticides (such as DDT) on crops?

  - pesticides can accumulate in the bodies of organisms over time. this is called bioaccumulation.

  - they are passed along the food chain

  - the toxicity increases to lethal levels
• What are two ways of increasing plant yield without using pesticides?

  - biological control

  - Create GM (genetically modified) crops that resist pests.
• What is an alternative to using fertilisers?

  We can use genetically modified (GM) crops that are better able to grow in low nitrate soils.
• What is biological control?


  The use of a predator or parasite to control a pest species.
• Give an example of biological control

  - Controlling aphids by releasing ladybirds (their predators)