31 Years NEET Previous Year Questions: Ecosystem - 1 Free MCQ Practice

Statement I: The primary source of energy in an ecosystem is solar energy.

• This statement is correct. Solar energy is the primary source of energy for most ecosystems. Producers (like plants) capture this energy and convert it into chemical energy through photosynthesis.

Statement II: The rate of production of organic matter during photosynthesis in an ecosystem is called net primary productivity (NPP).

• This statement is incorrect. The rate of production of organic matter during photosynthesis is termed gross primary productivity (GPP), not NPP.
• Net primary productivity (NPP) is the energy remaining after subtracting the energy used by producers for their own respiration from the gross primary productivity.
• Mathematically, NPP = GPP - Respiration (R).

• Ramdeo Misra is revered as the Father of Ecology in India. Born on 26 August 1908, Ramdeo Misra obtained Ph.D in Ecology (1937) under Prof. W. H. Pearsall, FRS, from Leeds University in UK.
• He established teaching and research in ecology at the Department of Botany of the Banaras Hindu University, Varanasi.
• His research laid the foundations for understanding of tropical communities and their succession, environmental responses of plant populations and productivity and nutrient cycling in tropical forest and grassland ecosystems.
• Due to his efforts, the Government of India established the National Committee for Environmental Planning and Coordination (1972) which, in later years, paved the way for the establishment of the Ministry of Environment and Forests (1984).

Other Options:

• S. R. Kashyap - Known for his work in bryology (study of mosses).
• Ram Udar - His contributions are mainly in the field of plant sciences.
• Birbal Sahni - A renowned paleobotanist known for his research on the fossils of the Indian subcontinent.

Statement I (Correct):

• Energy flow in an ecosystem is unidirectional. It originates from the sun, is captured by producers (plants) during photosynthesis, and then moves to consumers (herbivores, carnivores, and omnivores) and decomposers.
• Producers convert solar energy into chemical energy (e.g., glucose), which is then transferred to consumers when they eat plants or other consumers. Decomposers break down dead matter, releasing nutrients back into the environment but do not reverse the flow of energy.
• This unidirectional flow ensures energy is consistently passed through trophic levels but is never recycled back to the sun, adhering to the principle of energy flow in ecosystems.

Statement II (Incorrect):

• The Second Law of Thermodynamics applies to ecosystems. This law states that energy transformations lead to an increase in entropy (disorder), and some energy is always lost as heat during these processes.
• Ecosystems are not exempt from the Second Law of thermodynamics. They need a constant supply of energy to synthesise the molecules they require, to counteract the universal tendency toward increasing disorderliness.
• For example, when energy moves through trophic levels, a significant portion is lost as heat during respiration or metabolic activities. Only about 10% of the energy is transferred to the next trophic level, following the "10% law."

Productivity

• The amount of biomass or organic matter produced per unit area over a time period by plants, by the process of photosynthesis is called primary production.
• It is expressed in units of weight (g per m2) or energy (Kcal per m2).
• The rate of biomass production is called productivity and it is expressed as g m-2 yr-1 or (Kcal m-2) yr-1. 

Primary productivity is further divided into two categories:

• Gross Primary Productivity (GPP): The rate of production of organic matter during photosynthesis is called gross primary productivity. A large amount of GPP is lost by plants during respiration.
• Net Primary Productivity (NPP):It is defined as the difference between gross primary productivity and the respiration losses (R) by plants.
  • NPP = GPP - R;
  • It is the measure of net available biomass for heterotrophs (herbivores and decomposers).
  • Since net primary productivity is obtained after subtracting respiration losses from gross primary productivity; it is always less than gross primary productivity.

The pyramid of energy provided in the question represents how energy is transferred from one trophic level to the next in an ecosystem. Typically, there's an energy transfer efficiency of about 10% from one level to the next due to energy loss in the form of heat, metabolic processes, and other factors. This rule is often referred to as the 10% rule in ecology.
T₄ = 1000J
T₃= 10 x 1000 = 10,000J
T₂= 10 x 10000 = 1,00,000J
T₁ = 10 x 100000 = 10,00,000

Option C is correct.

Use the approximate 10% transfer efficiency: about 10% of production at one trophic level becomes production at the next trophic level.

Let NPP₁ = 100x kcal m^-2 yr^-1.

Then NPP₂ = 10% of NPP₁ = 10x kcal m^-2 yr^-1.

Then NPP₃ = 10% of NPP₂ = 1% of NPP₁ = x kcal m^-2 yr^-1.

Strictly, GPP = NPP + R (where R is respiration), so exact numeric value of GPP₃ cannot be calculated without knowing R. In standard energy-transfer problems of this type, the intended quantity is the production available at the third trophic level, taken as x kcal m^-2 yr^-1.

Therefore the correct choice is x kcal m^-2 yr^-1 (Option C).

Let's evaluate each statement:
A. Detrivores perform fragmentation.
This statement is true. Detrivores, such as earthworms and beetles, break down detritus (dead organic material) into smaller pieces in a process called fragmentation.

B. The humus is further degraded by some microbes during mineralization.
This statement is true. Microbes, including bacteria and fungi, break down humus into inorganic nutrients in a process called mineralization.

C. Water-soluble inorganic nutrients go down into the soil and get precipitated by a process called leaching.
This statement is true. Leaching refers to the process where nutrients are washed away from the soil into lower layers or into bodies of water.

D. The detritus food chain begins with living organisms.
This statement is false. The detritus food chain begins with dead organic material or detritus, not living organisms.

E. Earthworms break down detritus into smaller particles by a process called catabolism.
This statement is false. The process by which earthworms break down detritus into smaller particles is called fragmentation, not catabolism. Catabolism refers to the breakdown of complex molecules in living organisms to form simpler ones, along with the release of energy.

Therefore, the correct answer is : Option A: A, B, C only.