Meeting Global Food Demands (Edexcel GCSE Biology)

Higher Tier Only

• Modern technology has increased food supply substantially in a number of ways, including:
  • Agricultural machinery has replaced humans and improved efficiency due to the ability to farm much larger areas of land
  • Chemical fertilisers improve yields - fertilisers increase the amount of nutrients in the soil for plants, meaning that they can grow larger and produce more fruit
  • Insecticides and herbicides - these chemicals kill off unwanted insects and weed species, meaning that there is less damage done to plants and fruit lost to insects (insecticides), as well as reducing competition from other plant species (herbicides)
  • Selective breeding - animals and crop plants that produce a large yield are selectively bred to produce breeds that reliably produce high yields
• More recently, genetic engineering has been used to produced genetically modified crop plants that have increased yields compared to normal crop plants
  • These genetically modified crops are known as GM crops

Genetic engineering of crops

• Crop plants have been genetically modified to be:
  • Resistant to pests – increases productivity / yield
  • Resistant to herbicides – increases productivity / yield
  • Enriched in vitamins – increases the nutritional value

• Crop plants have been genetically modified to produce poisons that kill insects, making them resistant to insect pests. This can improve crop yields and reduce the need for chemical pesticides
  • For example, maize (corn) and cotton plants have been genetically modified with a gene for a toxin (a poison) that kills many insect larvae that are harmful to these crops
  • The toxin is called Bt toxin as it was taken from the bacterium Bacillus thuringiensis
  • The crops with the Bt gene produce the toxin in their stems and leaves
  • The significance of genetically engineering crops to be insect resistant is that there is an increase in yield and fewer pesticides are used which could have ecological benefits (e.g. non-targeted invertebrates are not harmed)

• Crop plants have also been genetically modified to make them resistant to certain herbicides (chemicals that kill plants)
  • This means that when the herbicide is sprayed on the crop it only kills weeds and does not affect the crop plant

• Some crops have been genetically modified to produce additional vitamins and improved nutritional value
  • For example, ‘golden rice’ contains genes from another plant and a bacterium which make the rice grains produce a chemical that is turned into vitamin A in the human body, which could help prevent deficiency diseases in certain areas of the world

• Some crops have been genetically modified to be drought-resistant (to grow better in very dry conditions). This can also improve crop yields in arid countries that are prone to droughts

Advantages & Disadvantages of GM Crops Table

Higher Tier Only

Using fertilisers to increase crop yields

• Plants require a range of mineral ions in order to grow well
• As crop plants take up these mineral ions from the soil, the mineral ions need to be replaced if crops are grown repeatedly in the same field (i.e. year after year)
• Fertilisers are used to replace these mineral ions
• They can make crops grow faster and bigger so that yields are increased
• Fertilisers can be in the form of organic fertiliser or chemical fertiliser
  • Organic fertilisers commonly used by farmers include farmyard manure and compost
  • Chemical fertilisers are often applied to the soil as dry granules or can be sprayed on in liquid form

• They mainly provide crop plants with nitrogen, phosphorus and potassium
• However, a major disadvantage is that excess fertilisers not taken up by crops can get washed into lakes and rivers and cause problems, such as eutrophication

Using biological control to increase crop yields

• Pests such as insects and other animals can damage crops by eating them
• Pests such as weeds can outcompete crop plants for space, water and soil nutrients
• Many of these pests can be controlled by introducing other species to the farmland (a technique known as biological control)
• Biological control can happen naturally - for example, ladybirds eat aphids (which can damage certain crops)
• Usually, a new species is introduced specifically to prey upon or parasitise the pest species - for example, cane toads were introduced into Australia to eat crop-damaging beetles and parasitic wasps can control whitefly in glasshouse tomato crops
• An advantage of biological control is that it can have longer-lasting effects than chemical pesticides and be less harmful to the environment (e.g. to non-target species)
• However, as biological control is based on a predator-prey cycle or a parasite-host relationship, it does not completely remove a pest but keeps it at lower levels
• Also, in some cases, the introduction of new organisms to an ecosystem can cause problems - for example, cane toads are now themselves considered a pest species in Australia as they poison the native species that eat them