BIOLOGY Volume 1 - A Guide to General Biology - 2004

8. HETEROTROPHIC NUTRITION

8.7. Human nutrition

8.7.5. Energy

About 80–85% of the energy intake in an average adult diet is provided by Introduction/36.html">CARBOHYDRATES and Lipids, with 15–20% coming from Proteins (and up to 5% potentially derived from alcohol). Under normal conditions, the body primarily utilizes the energy generated from The breakdown of carbohydrates and lipids. Energy is essential for:

1) maintaining basal METABOLISM, i.e., resting metabolism. This also includes the energy required for growth when necessary:

2) fueling physical activity (Muscle contraction);

3) generating heat to maintain a body Temperature of approximately 37 °С.

The majority of the energy acquired by the Organism is expended on maintaining basal metabolism.

8.7. Why does a mouse expend more joules per unit of body mass than a human?

8.8. It has been calculated that the reaction of 1 g of glucose with 774 cm3 of oxygen releases 15.8 kJ of heat, whereas the reaction of 1 g of a long-chain fatty acid with 2012 cm3 of oxygen releases 39.4 kJ of heat. Why does 1 g of a fatty acid release more than twice as much heat as 1 g of glucose?

Units of energy

The joule is the SI unit for measuring energy. Historically, energy was measured in calories.

4.18 J = 1 cal

1000 cal = 1 kcal (kilocalorie) = 1 Cal

1000 J = 1 kJ (kilojoule) = 1 J

1000 kJ = 1 MJ (megajoule)



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