<Dd> CO + H O + light → CH O + O </Dd> <Dd> CO + O + 4 H S → CH O + 4 S + 3 H O </Dd> <P> In both cases, the end point is a polymer of reduced carbohydrate, (CH O), typically molecules such as glucose or other sugars . These relatively simple molecules may be then used to further synthesise more complicated molecules, including proteins, complex carbohydrates, lipids, and nucleic acids, or be respired to perform work . Consumption of primary producers by heterotrophic organisms, such as animals, then transfers these organic molecules (and the energy stored within them) up the food web, fueling all of the Earth's living systems . </P> <P> Gross primary production (GPP) is the amount of chemical energy as biomass that primary producers create in a given length of time . (GPP is sometimes confused with Gross Primary productivity, which is the rate at which photosynthesis or chemosynthesis occurs .) Some fraction of this fixed energy is used by primary producers for cellular respiration and maintenance of existing tissues (i.e., "growth respiration" and "maintenance respiration"). The remaining fixed energy (i.e., mass of photosynthate) is referred to as net primary production (NPP). </P>

What is the difference between primary and non primary production