Read the passage and answer the following questions:
Apart from the deep-sea hydrothermal ecosystem, the primary source of energy for all ecosystems on Earth is the sun. However, only a portion of the incident solar radiation, less than 50 percent, is photosynthetically active radiation (PAR). Autotrophs, such as plants and photosynthetic bacteria, utilise this radiant energy to produce food from simple inorganic substances. Remarkably, plants can capture only 2-10 percent of the PAR, yet this small amount of energy sustains the entire living world. Understanding how solar energy, captured by plants, flows through different organisms within an ecosystem is crucial. In this unidirectional flow of energy, the sun nourishes the producers (often green plants), which serve as the foundation of the ecosystem. In terrestrial ecosystems, herbaceous and woody plants are the major producers, while in aquatic ecosystems, various species like phytoplankton, algae, and higher plants play this vital role. All other organisms, referred to as consumers or heterotrophs, depend on producers for their food requirements. Consumers can be classified based on their feeding habits. Those that directly consume producers, the plants, are called primary consumers. In contrast, if animals eat other animals that, in turn, feed on plants or their products, they are known as secondary consumers. Tertiary consumers, similarly, consume animals from the secondary consumer level. In summary, the entire ecosystem relies on the unidirectional flow of solar energy, starting from the sun to the producers (plants), and then passed on to the various levels of consumers, ensuring the sustenance of life within the ecosystem.
Choose the correct statements about the standing crop from the following:
A. Each trophic level has a certain mass of living material at a particular time, called the standing crop.
B. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area.
C. Measurement of biomass in terms of fresh weight is more accurate than in terms of dry weight.
D. The biomass of a species is expressed in terms of fresh or dry weight.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, B and D only
The standing crop is the mass of living material present at a trophic level at a particular time. It can be expressed as biomass or as the number of organisms in a unit area.
A. Each trophic level has a certain mass of living material at a particular time, called the standing crop. — True. This is the NCERT meaning of standing crop.
B. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area. — True. Both ways of measuring are given in the book.
C. Measurement of biomass in terms of fresh weight is more accurate than in terms of dry weight. — False. It is the other way. Measurement in terms of dry weight is more accurate, since the water content of fresh tissue can vary a lot.
D. The biomass of a species is expressed in terms of fresh or dry weight. — True. Both units are in use, though dry weight gives the better measure.
So A, B and D are correct.
NCERT Extract:
Energy Flow – “Each trophic level has a certain mass of living material at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area. The biomass of a species is expressed in terms of fresh or dry weight. Measurement of biomass in terms of dry weight is more accurate. Why?”