Secondary Productivity (AQA A Level Biology): Revision Note

Be careful not to confuse productivity with production.

• Productivity is a rate, so must have an associated time period

• Production has no unit of time, and is just energy or mass, per unit area or volume

A sunflower oil company wanted to know the primary productivity of their sunflower crop. They recorded the primary production of the crop each year for five years. This information is provided in the table below.

Calculate the average primary productivity of the sunflower crop over the time period, giving appropriate units.

Answer:

Step 1: calculate the total primary production over the time period

150 + 200 + 175 + 150 + 225 = 900

Step 2: calculate the average primary productivity

• This is the rate of production, or the production that occurs each year

• The production takes place over a five year period, so we divide the total production by five to determine production per year

900 ÷ 5 = 180

Step 3: give the appropriate units

• Units for productivity must include mass or energy, area and time:

180 kJ ha^-1 yr^-1

Don’t forget that in aquatic environments it may be more suitable to measure primary and secondary productivity per unit volume. E.g. for aquatic algae, primary productivity could be given in g m^-3 yr^-1.