How would you measure the amount of energy in an item of food?
How would you test for protein?
Find out more from the Food and Agriculture Organisation web site.
Adaptations of Cereals
The text below is adapted from material supplied by AQA.
Cereals are grains produced by plants belonging to the grass family. They account for over fifty per cent of human energy and protein needs, and cereal plants occupy two-thirds of all cultivated land. Cereals were the earliest cultivated plants and for over ten thousand years have been the staple food for many human societies. Their importance is related to a number of features. They are relatively easy to grow, store and transport and they have a high nutritive value. The table below shows the food values of some important cereals compared with those for some other plant foods. The figures show the amount of energy that can be obtained from and the total amount of protein and lipid present in 100 g. Most of the energy comes from starch and other carbohydrates and so the figures in the second column are a good measure of the amount of these substances present. Note how the energy figures and those for proteins and carbohydrates which relate to cereals are much higher than the figures for the other plants. Part of the reason for this is that cereal grains contain a very low proportion of water.
| Food crop |
Energy (kJ)
|
Protein (g)
|
Lipid (g)
|
| Wheat |
1420
|
12.0
|
2.0
|
| Rice |
1296
|
8.0
|
2.0
|
| Maize |
1471
|
10.0
|
4.0
|
| Sorghum |
1455
|
10.0
|
5.0
|
| Potatoes |
347
|
2.0
|
0.1
|
| Peas |
293
|
4.9
|
0.4
|
| Lettuce |
63
|
1.2
|
0.2
|
A third factor that contributes to the importance of cereals is that there are many species and varieties and these are grown in different parts of the world. Wheat and barley are found in temperate climates such as those of Europe, parts of Asia and North America. Maize grows best in hotter conditions and is an important cereal crop in many tropical areas. Rice is a crop of the wet tropics while sorghum can survive in very hot, dry conditions. All of these plants have adaptations which enable them to survive and grow well in particular environmental conditions. Some of these adaptations are structural while others involve the physiology of the plant.
You need to understand the adaptations of three plants; rice, maize and sorghum.