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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