food supply, plant growth and productivity 1

• Food security

  The ability of human populations to access food of sufficient quality and quantity
• Increase in human population and concerns for food security

  Leads to a demand for increased food production
• Food production

  • Must be sustainable and not degrade the natural resources on which agriculture depends
• Increasing food production

  1. Breeding of higher yielding cultivators

  2. Use of fertilisers

  3. Protect crops from pests, diseases and competition
• Crops developed by breeders

  • High nutritional values
  • Resistance to pests and diseases
  • Physical characteristics suited to rearing and harvesting
  • Able to thrive in particular environmental conditions
• The area to grow crops is quite limited
• All food production is dependent on photosynthesis and factors which control photosynthesis
• Crops grown

  • Cereals
  • Potatoes
  • Roots
  • Legumes
• Livestock production

  Produces less food per unit area than crop plants due to a loss of energy between trophic levels
• Livestock production is often possible in habitats unsuitable for growing crops
• Light energy

  Can be reflected, absorbed by photosynthetic pigments to generate ATP, or transmitted
• Each photosynthetic pigment absorbs different wavelengths of light
• Absorption spectra

  Shows the wavelength of light that each pigment absorbs
• Carotenoids

  Extend the range of wavelengths absorbed and pass the energy to chlorophyll for photosynthesis
• Action spectra

  Shows the relative rate of photosynthesis at different wave lengths of light
• Photosynthesis

  1. Absorbed light energy excites electrons in the pigment molecule

  2. Transfer of these electrons through the electron transport chain releases energy to generate ATP by ATP synthase
• Photolysis

  1. Uses light energy to split water into hydrogen ions and oxygen

  2. Oxygen is evolved (released)

  3. Hydrogen ions are transferred to the co-enzyme NADP to form NADPH
• Carbon fixation

  1. The enzyme RuBisCO fixes carbon dioxide by attaching it to ribulose bisphosphate (RuBP) producing 3-phosphoglycerate (3PG)

  2. The 3-phosphoglycerate is phosphorylated by ATP and combined with hydrogen ions from NADPH to form glyceraldehyde-3-phosphate (G3P)

  3. Glyceraldehyde-3-phosphate is used to regenerate RuBP and for the synthesis of glucose
• Glucose

  Can be used as a respiratory substrate, synthesised into starch or cellulose or passed to other biosynthetic pathways