1. Cereal Crops
Rice, Maize and Sorghum

2. 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

3. 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

4. Rice

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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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