Gross Primary Production (AQA A Level Biology): Revision Note

Remember that GPP is the stored chemical energy or biomass present in a given area or volume, so its units should include energy/mass, and area/volume.

If a unit also includes time, then this is a measure of productivity, which is not the same as production. (opens in a new tab)

The total biomass of the grass that grows in a 200 m² field is found to be 1000 kg.

Calculate the gross primary production of the grass field. Give appropriate units.

Answer:

Step 1: calculate the biomass of grass in 1 m² of the field

• 1m² is 1/200th of the field, so we divide the total field biomass by 200:

1000 ÷ 200 = 5 kg

Step 2: give the appropriate units

• Primary production is a measure of biomass per unit area or volume, so in this instance our units must include a mass and an area

5 kg m^-2

A patch of rainforest covering an area of 1 km² is estimated to contain 1500 kg of biomass.

Calculate the gross primary production of this rainforest patch. Give your answer in g m^-2.

Answer:

Step 1: calculate the biomass of 1 m² of the rainforest patch

• 1 km² = 1000 x 1000 = 1 000 000 m²

1500 ÷ 1 000 000 = 0.0015 kg

Step 2: convert this into grams

• 1 kg = 1000 g

0.0015 × 1 000 = 1.5 g m^-2

The biomass of aquatic algae in a tank is estimated to contain a total of 5440 joules of chemical energy. The tank has a volume of 4 m³.

Calculate the gross primary production of this aquatic algae. Give appropriate units.

Answer:

Step 1: calculate the chemical energy of the aquatic algae in 1 m³

5440 ÷ 4 = 1360 J

Step 2: give the appropriate units

• Note that we are dealing with aquatic plants, so the units will be volume rather than area

1360 J m^-3 OR 1.36 kJ m^-3