The thermodynamic necessity that for any organism, the energy intake (nutrients, light for photosynthesis, etc.) must equal the internal heat produced, the work (movement, transport, etc.) and growth (the difference between synthesis and degradation and between storage and depletion). Logical consequences of this equation are that a decrease in energy input will result in less work, and/or less growth or that an increase in energy input will result in greater heat generation and/or growth.