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

We are given:
NPP of first trophic level = 100x (kcal m^-2 yr^-1)

We are asked:
GPP of third trophic level = ?

Step 1: Understand terms

• GPP (Gross Primary Productivity): Total energy captured by producers.

• NPP (Net Primary Productivity): GPP minus energy lost in respiration (R).
  So,
  NPP = GPP − R

• First trophic level: Producers (plants).

• Third trophic level: Secondary consumers (carnivores).

Step 2: Energy flow between trophic levels

Only 10% of energy passes from one trophic level to the next (10% law).

So if NPP of producers (1st trophic level) = 100x,
then energy available to 2nd trophic level (primary consumers) = 10% of 100x = 10x.
And energy available to 3rd trophic level (secondary consumers) = 10% of 10x = x.

Step 3: GPP of 3rd trophic level

For heterotrophs (consumers), their GPP = total energy assimilated (food taken in).
Thus, GPP of 3rd trophic level = x (kcal m^-2 yr^-1).

Final Answer:

Correct Option: (b)
Answer:
x (kcal m^-2 yr^-1)

Solution:

• NPP of first trophic level = 100x

• 10% passed to 2nd trophic level = 10x

• 10% passed to 3rd trophic level = x
  Thus, GPP of 3rd trophic level = x (kcal m^-2 yr^-1).

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.

Topic in NCERT: Decomposition

Line in NCERT: "this process is called fragmentation. by the process of leaching, water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts. bacterial and fungal enzymes degrade detritus into simpler inorganic substances. this process is called as catabolism. humification and mineralisation occur during decomposition in the soil. humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. the humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation."

In the equation GPP - R = NPP,
GPP stands for Gross Primary Productivity, NPP stands for Net Primary Productivity, and R represents the energy used by plants for their own metabolic processes, which is also known as Respiratory loss.

Topic in NCERT: Primary productivity

Line in NCERT: "gross primary productivity minus respiration losses (r), is the net primary productivity (npp).
Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). GPP – R = NPP Net primary productivity is the available biomass for the consumption to heterotrophs (herbiviores and decomposers)."

• Decomposition is the process by which decomposers breakdown complex organic matter into inorganic substances.
• The rate of decomposition is controlled by chemical composition of detritus and climatic factors. Decomposition is slower if detritus is rich in lignin and chitin and quicker, if detritus is rich in nitrogen and water soluble substances like sugars.

Topic in NCERT: Decomposition

Line in NCERT: "decomposition is largely an oxygen-requiring process. the rate of decomposition is controlled by chemical composition of detritus and climatic factors. in a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water-soluble substances like sugars."

(Detritivores break down detritus into smaller particles) e.g. earthworm. This process is called fragmentation.

Topic in NCERT: Decomposition

Line in NCERT: "detritivores (e.g., earthworm) break down detritus into smaller particles. this process is called fragmentation."

To solve the question, we need to identify the term that describes the amount of biomass or organic matter produced per unit area over a specific time period by plants during photosynthesis.

1. Understanding the Terms:
- We need to understand the definitions of the terms provided in the options: primary productivity, secondary productivity, standing state, and standing crop.

2. Defining Primary Productivity:
- Primary productivity refers to the rate at which biomass is produced by autotrophs (like plants) during photosynthesis. It is measured as the amount of organic matter produced per unit area over a specific time period.

3. Evaluating Other Options:
- Secondary Productivity: This refers to the rate of formation of new organic matter by consumers (herbivores and carnivores) and is not relevant to the question.
- Standing State: This term refers to the amount of nutrients present in the soil at any given time, which does not pertain to biomass production.
- Standing Crop: This refers to the total mass of living material (biomass) present at a specific time in a particular area, but it does not measure the rate of production over time.

4. Conclusion:
- Based on the definitions, the correct answer to the question is Primary Productivity, as it specifically refers to the biomass produced by plants through photosynthesis over a given area and time.

Final Answer:
The amount of biomass or organic matter produced per unit area over a time period by the plants during photosynthesis is called Primary Productivity.

• A-II: Lion, a tertiary consumer.
• B-III: Wolf, as a secondary consumer.
• C-IV: Goat, a primary consumer.
• D-I: Grass, a primary producer.

Statement I: "The rate of decomposition is not related to chemical composition of detritus and climatic factors."

• Analysis: This statement is false. The rate of decomposition is heavily influenced by both the chemical composition of detritus (such as the presence of lignin, chitin, nitrogen, and other compounds) and climatic factors (such as temperature, moisture, and the presence of decomposers). Materials rich in lignin and chitin decompose slower due to their complex structures that are more resistant to breakdown, whereas materials rich in simpler compounds like sugars decompose faster. Climatic conditions like warmer temperatures and higher moisture levels generally accelerate decomposition processes.

Statement II: "In a particular climatic condition, decomposition rate is faster if detritus is rich in lignin and chitin."

• Analysis: This statement is false. The decomposition rate is actually slower if detritus is rich in lignin and chitin. These compounds are more complex and harder for decomposers to break down compared to simpler, more nutrient-rich compounds.

The gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. Some of this organic matter is lost because of the respiration of plants. The remaining primary productivity is the net primary productivity.

Topic in NCERT: Productivity

Line in NCERT: "gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. a considerable amount of gpp is utilised by plants in respiration. gross primary productivity minus respiration losses (r), is the net primary productivity (npp)."

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

Pyramid of biomass in an aquatic ecosystem (e.g., pond, sea) is usually inverted because the biomass of fishes exceeds the biomass of phytoplanktons.

Topic in NCERT: Pyramid of biomass

Line in NCERT: "the pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton."

The given data depicts the inverted pyramid of biomass, usually found in aquatic ecosystem. This can be understood by taking an example of a pond in which phytoplankton (10g) represents the producer. Small fishes (60g) feeding upon these phytoplankton represent primary consumers which are further eaten by the big fishes (120g) representing secondary consumers.

Topic in NCERT: Pyramid of biomass

Line in NCERT: "the pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton."

• Stratification is the occurrence of vertical zonation in the ecosystem & indicates the presence of favorable environmental conditions.
  Example: Trees occupy top vertical strata or layer of a forest, shrubs the second. Herbs & grasses occupy the bottom layers.
• It is absent or poor where environmental conditions are unfavorable.
  Example: Desert ecosystems have very few trees & shrubs.

Topic in NCERT: Ecosystem

Line in NCERT: "vertical distribution of different species occupying different levels is called stratification."

Standing crop is the amount of living biomass in an ecosystem. It indicates the productivity & luxuriance of growth. It is expressed in the form of number or biomass of organisms per unit area

Topic in NCERT: Trophic levels in an ecosystem

Line in NCERT: "each trophic level has a certain mass of living material at a particular time called as the standing crop."

Gross Primary Productivity (GPP) is the rate of production of biomass or accumulation of energy by green plants per unit area per unit time. GPP depends on the chlorophyll content.

Topic in NCERT: Productivity

Line in NCERT: "gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis."