The correct option is Less than 50 % of the incident solar radiation.
Explanation
Solar radiation is the primary source of energy for all ecosystems on Earth (except deep-sea hydrothermal vents). However, not all wavelengths of the solar spectrum are utilized by plants. The specific portion of the light spectrum that plants use for photosynthesis is known as
Photosynthetically Active Radiation (PAR).
Statement-wise Analysis
- Less than 50 % of the incident solar radiation is Correct: According to ecological principles, less than 50 % of the total incident solar radiation falls within the Photosynthetically Active Radiation (PAR) range. This range corresponds to wavelengths between 400 nm and 700 nm (the visible spectrum). Plants capture only about 2-10 % of this PAR to sustain the entire living world.
- The entire incident radiation at Earth’s surface is Incorrect: Plants cannot utilize the entire spectrum. Wavelengths outside the visible range (such as ultraviolet and infrared) are generally not suitable for the photochemical reactions involved in photosynthesis.
- Only ultraviolet wavelengths of the spectrum is Incorrect: Ultraviolet (UV) radiation has shorter wavelengths and higher energy than visible light. It is typically harmful to plant tissues and DNA, rather than being a source of energy for photosynthesis.
- Only infrared wavelengths of the spectrum is Incorrect: Infrared (IR) radiation has longer wavelengths than visible light and is primarily experienced as heat (thermal energy). It does not carry sufficient energy to excite electrons in chlorophyll molecules to drive photosynthesis.
Key Takeaway
Photosynthetically Active Radiation (PAR) constitutes
less than 50% of the total incident solar radiation on Earth. It corresponds to the visible light spectrum (400-700 nm).