Environmental Engineering Reference
In-Depth Information
Table 22.2 Energy content of various plants and foods (kJ 100
g −1 )
Plants and crops
Potato
1646
Oats (seed)
1774
Mustard (seed)
2532
Green algae
2280
Sunflower (seed)
2829
Pine (seed)
2507
Spartina grass
1707
Wheat (seed)
1793
Foodstuffs
Brown wheat flour
1377
Oatmeal
1587
Cornflour
1508
Whole milk
275
Double cream
1850
Cheddar cheese
1708
Brie
1323
Vanilla ice cream
814
Fats and oils
Butter
3031
Olive oil
3696
Rape seed oil
3696
Lard
3663
numbers, measuring their weights and sizes, and determining their energy contents in the
laboratory using a calorimeter. All data for plants and animals can be expressed as energy
equivalents . Note that one calorie per gram is equivalent to 4·186 joules per gram (1 cal
g −1 = 4·186 J g −1 ), although usually energy content is expressed as kilocalories, where 1
kcal = 1000 cal or 4186 J. Figure 22.4 is an energy flow diagram for Wytham Wood,
Oxfordshire. This famous deciduous woodland consists of oak and other species, with an
understorey of shrubs and a ground flora of herbs. All figures in the diagram are
thousands of joules per square metre per year (kJ m −2 yr −1 ). The values within the boxes
are for primary and secondary production (P); the values in circles are for consumption
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