Primary productivity is the rate of primary production, and secondary productivity is the rate of

secondary production.

Both values are measured as biomass in a given area in a given time.

For instance, the units may be kJ ha^-1 year^-1.

The chemical energy store in dry biomass can be estimated using calorimetry. 

Using calorimetry to measure biomass:

1. Dry the biomass sample until its mass remains constant to obtain the dry mass
2. Weigh the dry mass
3. Burn the dry mass in a calorimeter
4. Measure the volume and temperature change of the surrounding water
5. Use these values to calculate an estimate of the heat energy released from the burnt biomass

Agriculture involves manipulating the environment to favour plant species that we can eat (crops) and to rear animals for food or their produce.

This creates simple food chains by reducing the number of trophic levels, ensuring as much energy as possible is transferred into biomass that can be eaten by humans.

Ecological efficiency refers to the percentage efficiency at which biomass or energy is transferred from one trophic level to the next.

ecological efficiency =energy or biomass available before transferenergy or biomass available after transfer​×100%

Biomass is the total mass of living material present at a given time in a specific place or in specific organisms. Biomass can be equated to energy content.

Biomass is measured in grams per square metre (g m^-2) for areas of land.

Biomass is measured in grams per cubic metre (g m^-3) for areas of water.

A trophic level refers to each stage in a food chain or food web, representing the transfer of biomass and energy through the organisms in an ecosystem.

1. Producers - make their own food, e.g. by converting light energy, water, and carbon dioxide into biomass
2. Primary consumers - consume producers
3. Secondary consumers - consume primary consumers
4. Tertiary consumers - consume secondary consumers

A food web is a network of interconnected food chains within a single ecosystem.

The arrows in a food web represent the flow of energy from one organism to another.

Saprobionts are organisms that break down complex materials in dead organisms into simple ones, releasing nutrients back into the ecosystem.

GPP is the total quantity of solar energy that plants convert to organic matter and store as chemical energy in plant biomass.

NPP is the chemical energy store that is available to the next trophic level after respiratory losses have been taken into account. It is the energy converted into biomass.

Net primary production (NPP) = gross primary production (GPP) - respiratory losses (R)

The total amount of biomass decreases at each trophic level moving up a food chain, because not all energy is transferred up trophic levels, so higher trophic levels have less energy to produce biomass.

These energy losses may occur due to:

1. Some solar energy is transmitted through leaves or isn't the correct wavelength for photosynthesis
2. Other factors, like water availability, limit photosynthesis
3. Some energy is lost during photosynthetic reactions
4. Not all biomass is edible or digestible by consumers
5. Some energy is lost to the environment as heat during movement or respiration
6. Some energy is lost in excretory materials like urine and faeces

N = I − (F + R)

N: net production

I: chemical energy store of ingested food

F: energy lost in faeces and urine

R: energy lost in respiration