Thermodynamics & Energy
The basic principles of thermodynamics and how food provides energy.
Energy
Energy is the capacity to supply heat or do work. There are two major types of energy: potential and kinetic. Potential energy is the energy an object possesses due to its position, composition, or condition. Kinetic energy is the energy an object possesses due to its motion. For example, a cart at the top of a roller-coaster has potential energy due to its position. When the cart drops down the hill, it has kinetic energy due to its movement.
Thermodynamics
Thermodynamics is the study of energy and energy transfer. As we discussed in “Metabolism,” energy is transferred through the food chain: primary producers (autotrophs) to consumers (heterotrophs) to decomposers. The Law of Conservation of Energy states that the total amount of energy in the world remains constant; energy in neither created nor destroyed only transferred or transformed. For example, the potential energy within wood is transformed into heat energy during combustion.
Food for Energy
The energy that is required for regular bodily processes is obtained from the food we eat. We measure this energy in calories. Different nutrients contain varying amounts of energy. As listed below, carbohydrates contain 9 calories of energy per gram, while lipids and proteins contain 4 calories per gram.
Carbohydrate
9 calories/gram
Lipids
4 calories/gram
Proteins
4 calories/gram
The energy we obtain from food is first used to maintain bodily functions, including continuing brain activity, functioning organs, and maintaining body temperature. All of these functions are necessary for life. Because of this, there is a minimum amount of calories we must intake daily in order for our bodies to run properly. This minimum is known as the Basal Metabolic Rate (BMR), which is determined by age and weight. As discussed previously, energy cannot be destroyed. Any excess energy (greater than the BMR), will either be burned off during activity or accumulated in chemical form as fat or glycogen.
For more information, visit Chapter 6 of Biology 2e & Chapter 5 of Chemistry 2e.
