In biology, <answer>energy</answer> is an attribute of all biological systems from the biosphere to the smallest living organism. Within an organism it is responsible for growth and development of a biological cell or an organelle of a biological organism. Energy is thus often said to be stored by cells in the structures of molecules of substances such as carbohydrates (including sugars), lipids, and proteins, which release <answer>energy</answer> when reacted with oxygen in respiration. In human terms, the human equivalent (H-e) (Human <answer>energy</answer> conversion) indicates, for a given amount of <answer>energy</answer> expenditure, the relative quantity of <answer>energy</answer> needed for human metabolism, assuming an average human <answer>energy</answer> expenditure of 12,500 kJ per day and a basal metabolic rate of 80 watts. For example, if our bodies run (on average) at 80 watts, then a light bulb running at 100 watts is running at 1.25 human equivalents (100 ÷ 80) i.e. 1.25 H-e. For a difficult task of only a few seconds' duration, a person can put out thousands of watts, many times the 746 watts in one official horsepower. For tasks lasting a few minutes, a fit human can generate perhaps 1,000 watts. For an activity that must be sustained for an hour, output drops to around 300; for an activity kept up all day, 150 watts is about the maximum. The human equivalent assists understanding of <answer>energy</answer> flows in physical and biological systems by expressing <answer>energy</answer> units in human terms: it provides a "feel" for the use of a given amount of <answer>energy</answer>.
In biology, what is an attribute of all biological systems from the biosphere to the smallest living organism?
energy