Let's break down the question on primary productivity in an ecosystem.
Primary productivity is an important concept in ecology and it refers to the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances. It is a crucial metric that helps ecologists understand the energy base of an ecosystem.
Given the options:
- The number of plants or other producers growing per unit area per year: This refers to the density or the count of producers in a particular area over time. However, it doesn't capture how much energy or material these producers are actually synthesizing from inorganic sources.
- How large in meters the producers get, on average: This option refers to the average size or height of the producers. While size can be an indicator of growth and potentially productivity, it doesn't directly measure the total material or energy produced.
- The amount of material (mass) made by producers per unit area per year: This option directly addresses the rate at which producers convert inorganic substances into organic material. This is indeed the standard definition of primary productivity. It measures the biomass created by producers in a given area over a specific time period.
Therefore, the correct way to measure primary productivity in an ecosystem is by the amount of material (mass) made by producers per unit area per year.
So, the correct answer is:
c) the amount of material (mass) made by producers per unit area per year
