1. Cereal Crops: Rice, Sorghum and Maize

2. Nutritive values of cereal crops
Energy (kJ/100g)
Protein (g/100g)
Lipid (g/100g)
wheat
1420
12.0
2.0
rice
1296
8.0
maize
1471
10.0
4.0
sorghum
1455
5.0
potatoes
347
2.0
0.1
peas
293
4.9
0.4
lettuce 63
1.2
0.2
After Inge, Rowland and Baker: A New Introduction of Biology

3. Rice Rice is grown in paddy fields.
It is adapted for survival in waterlogged conditions. Most plants (including weeds as a bonus) would die in these conditions as they are obligate aerobes.
The roots of rice plants are able to use anaerobic respiration and can tolerate high ethanol concentrations produced as a result.
The stem is hollow, while leaves, stems and roots have air spaces in tissues called aerenchyma. This gives floatation and support and allows oxygen to diffuse through the plant.

4. Cross-section of the stem of a rice plant
Air spaces in aerenchyma tissue
Hollow centre
Cross-section of the stem of a rice plant

5. Maize
Maize is a tropical plant (originally from Mexico area of Central America) adapted for high temperatures, high humidity and high light intensity. (Some varieties have been developed for temperate climates now)
It is adapted to conserve water. The leaves can roll up to reduce exposure of stomata. Stomata are also closed more of the time.
Closed stomata reduce the rate of transpiration, and also reduce uptake of carbon dioxide by diffusion.
Maize must be adapted to overcome these problems:

6. Maize
Maize has evolved a photosynthetic pathway which works well at high temperatures and low CO2 concentrations (this is the C4 pathway).
Most other plant species use the C3 photosynthetic pathway (C3PO)
You don’t have to learn the photosynthetic pathways at AS level!

7. Sorghum
Sorghum is a xerophyte – it is adapted to live in very hot, dry conditions (very important crop in sub-Saharan Africa and the Indian sub-continent). It is adapted to conserve water:
1. Long, extensive root system to reach deep
into the soil to find water.
2. Thick waxy cuticle.
3. Few stomata.
4. Sunken stomata to allow water vapour to build up around them – reduces transpiration.
5. Leaves that roll up like maize.
6. It is also adapted to use the C4 pathway.
7. Uses thermostable enzymes.

8. Plenary Look at the samples of cereal plants grown by the technicians
Draw graphs of photosynthetic rate against light intensity, temperature and carbon dioxide concentration respectively
Relate the adaptations of rice, maize and sorghum to each of these factors