Introduction

Photosynthesis is the process by which plants convert sunlight into chemical energy, forming the foundation of nearly all life on Earth. However, despite the abundance of sunlight, plants are surprisingly inefficient at converting light energy into usable biomass. This article explores what percentage of photosynthetically active radiation (PAR) is actually utilized for photosynthesis by plants.

What Is Photosynthetically Active Radiation (PAR)?

Photosynthetically active radiation (PAR) refers to the range of light wavelengths (400–700 nm) that plants can use for photosynthesis. Not all sunlight that reaches a plant is within this range, and not all PAR that reaches a plant is absorbed or converted into biomass.

How Efficient Is Photosynthesis at Using PAR?

When sunlight hits a plant, several factors reduce the efficiency of photosynthesis:

• Only about 45–53% of sunlight is within the PAR range.

• Plants absorb only about 34–37% of incident PAR (the rest is reflected or passes through the leaf).

• Even the absorbed PAR is not fully converted into biomass due to energy losses in the photosynthetic process, respiration, and other metabolic activities126.

What Percentage of PAR Is Actually Used for Photosynthesis?

After accounting for all these losses, the percentage of incident PAR that is actually converted into biomass by plants is typically in the range of 1–3% under natural conditions. Some highly productive crops or optimized laboratory conditions may approach the higher end of this range, but most plants do not exceed it167.

Why Is Photosynthesis So Inefficient?

Several factors contribute to the low efficiency of photosynthesis:

• Only a portion of sunlight is within the PAR range.

• Not all PAR is absorbed by the plant.

• Energy is lost during the conversion of light energy into chemical energy.

• Plants use energy for respiration and other metabolic processes.

• Excess light energy is dissipated as heat to protect the plant from damage56.

Comparison to Other Energy Conversion Systems

By comparison, solar panels convert sunlight into electricity at efficiencies of 6–20% for mass-produced panels, and over 40% in laboratory settings. Plants, however, are limited by the constraints of biological systems and the need to dissipate excess energy to avoid damage7.

Implications for Agriculture and Ecology

The low efficiency of photosynthesis has important implications for agriculture and ecology. It limits the amount of biomass that can be produced per unit area of land, which in turn affects food production and ecosystem productivity. Researchers are actively exploring ways to increase photosynthetic efficiency to boost crop yields and address global food security challenges5.

Conclusion

Most plants utilize only 1–3% of incident photosynthetically active radiation (PAR) for photosynthesis and biomass production. This low efficiency is due to a combination of physical, biochemical, and metabolic limitations. Understanding these factors is essential for improving agricultural productivity and managing natural ecosystems.

Correct answer:
(2) 1–3