Previous Year Question
With reference to ‘Ecosystem’, which of the following statements is/are correct?
Green plants in terrestrial ecosystem capture about 1% of energy of the sunlight that falls on their leaves.
Around 10% of organic matter reaches to the next higher level of consumers.
Select the correct answer from the code given below:
Only 2
Neither 1 nor 2
Both 1 and 2
Only 1
Correct Answer: C
Detailed Solution
Statement 1 is correct. In a Terrestrial Ecosystem, green plants act as Primary Producers, converting solar energy into Chemical Energy through Photosynthesis. Green plants convert approximately 1% of the sunlight energy falling on their leaves into Food Energy. During this process, Chlorophyll helps absorb light energy, which is utilized to synthesize carbohydrates from carbon dioxide and water. Most of the incoming solar energy is not stored as food, and a portion remains unavailable because of reflection, transmission, and other processes.
Statement 2 is also correct. In an ecosystem, energy is transferred through different Trophic Levels of a Food Chain. According to Lindeman's 10% Law, approximately 10% of the energy available at one trophic level is transferred to the next higher trophic level on average. A large proportion of the remaining energy is expended through Respiration, Digestion, physical activities, and heat loss. This 10% represents an average estimate rather than a fixed proportion across all ecosystems.
Energy Flow generally follows the direction Sun → Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers. For example, if 10,000 J of energy is available at the producer level in a food chain, approximately 1,000 J may be available to primary consumers, 100 J to secondary consumers, and 10 J to tertiary consumers, according to the 10% rule. Because energy availability decreases at each successive trophic level, food chains are generally limited to three or four trophic levels. Due to this progressive energy loss, the Pyramid of Energy is always Upright.
Primary Productivity represents the rate at which plants produce organic matter over a specified period. Gross Primary Productivity (GPP) refers to the total energy captured or organic matter produced through photosynthesis, whereas Net Primary Productivity (NPP) is the productivity remaining after subtracting the energy consumed in plant respiration. According to NCERT Class 12, less than 50% of incoming solar radiation is Photosynthetically Active Radiation (PAR), and plants can capture approximately 2–10% of this PAR. This percentage refers to the available PAR, whereas the approximately 1% figure in Statement 1 refers to the conversion of total sunlight energy falling on leaves into food energy.