Primary Producers

What are primary producers?

Living systems operate by expending energy. Organisms need energy for growth, reproduction, and their own metabolic processes. In short, if there is no energy, there are no life functions! Yet, no organism can create energy—organisms can only use energy from other sources. You probably know that you get your energy from the plants and animals you eat. But where does the energy in your food come from? For most life on Earth, sunlight is the ultimate energy source. Over the last few decades, however, researchers have discovered that there are other energy sources for life. For some organisms, chemical energy stored in inorganic chemical compounds serves as the ultimate energy source for life processes.

Only algae, certain bacteria, and plants like the one in Figure 3–4 can capture energy from sunlight or chemicals and convert it into forms that living cells can use. These organisms are called autotrophs. Autotrophs use solar or chemical energy to produce “food” by assembling inorganic compounds into complex organic molecules. But autotrophs do more than feed themselves. Autotrophs store energy in forms that make it available to other organisms that eat them. That's why autotrophs are also called primary producers.

Primary producers are the first producers of energy-rich compounds that are later used by other organisms. Primary producers are, therefore, essential to the flow of energy through the biosphere.

Figure 3–4 Primary Producers Plants obtain energy from sunlight and turn it into nutrients that can, in turn, be eaten and used for energy by animals such as this caterpillar.