IB Environmental systems and societies: Unit 2 (2.3)

Productivity

Productivity

The rate of generation of biomass in an ecosystem, usually expressed in units of mass per volume (unit surface) per unit of time, such as grams per square meter per day.

Primary productivity

The rate at which energy is converted to organic substances by photosynthetic producers or the increase in biomass per unit area per unit time.

Secondary productivity

The rate of biomass production by consumers or herbivores.

Gross productivity

The overall gain of energy captured or biomass per unit area per unit time

Net Productivity

Gain of energy or biomass after respiration. Shows energy available for the next trophic level.

Net primary productivity (NPP)

• The difference between all the carbon fixed by primary producers (plants) and the part of that fixed carbon that the primary producer uses for its own cellular respiration needs.

• The rate at which plants convert captured energy into biomass, minus the energy they expend through cellular respiration.

• Represents the amount of energy available for consumption by herbivores and for storage in plant tissues.

• NPP=GPP-Respiration

• Where Gross Primary Productivity (GPP) is the total amount of energy, mainly from sunlight, that plants in an ecosystem capture and convert into food via photosynthesis over a certain period

Gross secondary productivity

Gross secondary productivity (GSP) is the total energy or biomass assimilated by consumers and is calculated by subtracting the mass of fecal loss from the mass of food consumed.

• GSP = food eaten – fecal loss.

Net Secondary Productivity

Can be found through measuring the increasing in biomass in primary consumer over a specific amount of time.

• NSP = GSP - R

Where Gross secondary productivity (GSP) is the total energy or biomass assimilated by consumers and is calculated by subtracting the mass of fecal loss from the mass of food consumed. This is shown by the equation GSP = food eaten – fecal loss.

Nitrogen cycle

• Nitrogen fixation: Lightning and bacteria convert nitrogen gas (N2) into ammonia (NH3) or ammonium (NH4+).

• Nitrification: Bacteria convert ammonia or ammonium into nitrite (NO2-) and then into nitrate (NO3-).

• Nitrogen assimilation: Plants and animals take up nitrate and use it to make proteins and other organic molecules.

• Ammonification: Decomposers break down organic matter and release ammonia or ammonium back into the soil.

• Denitrification: Bacteria convert nitrate into nitrogen gas, which returns to the atmosphere.