Cereal Crops



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Cereal Crops

  • Rice, Maize and Sorghum

Cereals- the worlds staple foods

  • Cereals are all members of the grass family
  • Examples include rice, wheat, maize and sorghum
  • They are grown for their seeds (grains) which are high in carbohydrates and protein
  • The water content of the grains is low compared to other vegetables

Other benefits of cereals

  • Easy to store because the low water content helps prevent mould growth
  • Easy to transport because there is not a lot of wet bulk
  • There is a suitable cereal for each type of climate

Rice

Rice

  • Grown in areas of high temperature and high humidity
  • Small plants are planted out in flooded fields
  • Rice can grow in normal soil
  • Flooded fields reduce competition from weeds
  • Nitrogen fixing bacteria live on flooded rice roots providing nitrate. This reduces need for fertiliser

Adaptions of rice to waterlogging

  • Roots contain air spaces to conduct oxygen from the air down into the roots. This tissue is called aerenchyma
  • Root cells are tolerant of ethanol which is the waste product from anaerobic respiration by root cells when oxygen is lacking

Sorghum

  • This is a cereal which is adapted to grow in arid (dry) regions and tolerate high temperatures and light intensities
  • Uses a quarter of the water needed by rice
  • Has a lower grain yield than cereals grown in areas where water is abundant but is often the only crop that will grow

Adaptions of sorghum to drought

  • Extensive root system
  • Thick cuticle (waxy layer covering leaves) reduces evaporation of water from leaves
  • Sunken stomata reduce water loss by evaporation
  • Stomata close during drought and reopen very quickly afterwards

Adaptions of Sorghum to heat

  • Sorghum plants can synthesis heat shock proteins rapidly when temperatures rise
  • These heat shock proteins prevent enzymes being denatured and make them more thermostable

Adaptions of sorghum to high light intensity

  • Sorghum plants carry out C4 photosynthesis
  • This means that when carbon dioxide is absorbed into leaf cells it combines with molecules in the cells to make a molecule containing 4 carbon atoms

C3 and C4 photosynthesis

  • In temperate regions like the UK most plants are C3
  • This means that the first molecule made when CO2 enters the leaf cells has 3 carbon atoms
  • C4 photosynthesis is an advantage to plants in hot regions with high light intensity

Advantages of C4 photosynthesis

  • A different enzyme is used. C3 plants use the enzyme rubisco which is not very effective when CO2 concentrations in the leaf cells are relatively low.
  • C4 plants use the enzyme PEP this enzyme has a high affinity for CO2 even when concentrations are low, for example when plants close their stomata to reduce water loss

And finally Maize

  • Another C4 plant which is able to photosynthesis efficiently at high temperatures and light intensities.
  • Needs more water than sorghum but gives a higher yield so the preferred crop wherever there is enough rainfall
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