Transcript Cereal Crops - World of Teaching

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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