What's the Difference Between Gross Productivity and Net Productivity?

Gross productivity (GP) is the total gain in biomass by an organism, while net productivity (NP) is the biomass remaining after losses through cellular respiration. Therefore, net productivity is always lower than gross productivity when respiration occurs.

This distinction is part of IB ESS subtopic 2.2 Energy and biomass in ecosystems and is required at both SL and HL.

The Relationship

Organisms convert energy into chemical energy stored in biomass. However, they use some of this stored chemical energy in cellular respiration to support processes such as growth, movement, active transport and temperature regulation.

The relationship is:

$$\text{NP} = \text{GP} - \text{respiratory losses}$$

The size of the difference between GP and NP reflects the organism’s respiratory demand: greater respiratory losses leave less biomass for growth, reproduction and consumption by organisms at the next trophic level. Temperature and activity can influence this demand.

For example, suppose an organism has a gross productivity of $1{,}200\text{ g m}^{-2}\text{ year}^{-1}$ and loses the biomass equivalent of $500\text{ g m}^{-2}\text{ year}^{-1}$ through respiration:

$$\text{NP} = 1{,}200 - 500 = 700\text{ g m}^{-2}\text{ year}^{-1}$$

The organism therefore retains $700\text{ g m}^{-2}\text{ year}^{-1}$ as net productivity. This remaining biomass may contribute to growth or become available to consumers through feeding.

A common misconception is that gross productivity is the biomass already available to the next trophic level. This is incorrect because respiratory losses must first be subtracted. Productivity also affects human decisions: harvesting biomass faster than it is replenished reduces natural capital and may make resource use unsustainable.

Exam Technique

For an explain or calculation question, define both terms, state the relationship, show the subtraction and include units. Use the 2026 syllabus abbreviations GP and NP, not older terms such as GPP or NPP unless the question specifically refers to primary productivity, which is HL-only content.