Final answer:
Basal metabolism is the energy used to maintain basic life functions while at rest, with the basal metabolic rate (BMR) being the rate of energy consumption by the body to perform these functions. The liver and spleen use the majority of this energy, and factors like muscle mass and age can influence an individual's BMR.
Step-by-step explanation:
Basal metabolism refers to the energy used to sustain life during rest. The basal metabolic rate (BMR) is the total energy conversion rate of a person at rest, necessary to maintain the basic functions of the body. Approximately 75% of the calories we consume are used to support these vital functions, which are spread among the body's systems, with the largest fraction being utilized by the liver and spleen, followed by the brain.
The BMR is influenced by several factors including age, gender, body composition, and muscle mass. Athletes or individuals with higher lean body mass tend to have a higher BMR, as muscle tissue requires more energy to maintain than fat tissue. With age, BMR generally declines due to a decrease in lean muscle mass.