What are the two main components used to express primary productivity?

Weight and energy

The correct answer is (a) Weight and energy.

The two main components used to express primary productivity are weight and energy. These components help quantify the amount of biomass or organic matter produced per unit area over a given time period by plants during photosynthesis.

1. Weight: Weight refers to the measurement of primary productivity in terms of the physical mass or biomass of organic matter produced by plants. It is typically expressed in units such as grams per square meter (g m^–2). Weight-based measurements provide information about the total amount of organic material produced by plants in a given area.
2. Energy: Energy refers to the measurement of primary productivity in terms of the energy content of the organic matter produced by plants. It is often expressed in units such as kilocalories per square meter (kcal m^–2) . Energy-based measurements provide insights into the amount of available energy that can be utilized by organisms in the ecosystem.

Both weight and energy measurements are important for understanding the productivity and functioning of ecosystems. Weight-based measurements give an indication of the physical biomass available as a food source for consumers, while energy-based measurements provide insights into the flow of energy through the food web and the potential energy available for sustaining life processes.

It's worth noting that primary productivity can also be measured in other units, such as carbon fixation (grams of carbon per square meter) or oxygen evolution (milligrams of oxygen per liter). However, weight and energy are the two primary components commonly used to express primary productivity and compare productivity levels across different ecosystems.

In summary, weight and energy are the two main components used to express primary productivity. Weight represents the biomass or organic matter produced by plants, while energy reflects the available energy content of the produced biomass. These measurements provide valuable insights into the productivity and energy flow within ecosystems.