Cereal Crops

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Cereal Crops

• Rice, Maize and Sorghum

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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

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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

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Rice
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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

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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

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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

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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

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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

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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

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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

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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

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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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