How much energy is defined as the calorie?

The calorie is defined specifically as the amount of energy required to raise the temperature of 1 kilogram of water by 1 degree Celsius. This definition is foundational in the field of nutrition and thermodynamics, as it establishes a standard unit of measurement for heat energy.

Using this definition, when 1 kilogram of water is heated from, say, 20 degrees Celsius to 21 degrees Celsius, it requires a specific amount of energy that corresponds to one calorie. This quantification allows for a clear and practical understanding of energy transfer, particularly in calculations involving food energy, metabolism, and exercise.

In contrast, the other responses present variations of this concept but do not align with the precise definition of a calorie. For example, raising the temperature of 1 kg of water by 2 degrees would require twice the energy of 1 calorie, and measuring energy in relation to 100 grams of water or the cooking of food introduces different contexts that deviate from the strict definition of a calorie.