Test: Ecosystem - 1 - NEET MCQ

In the ecosystem, the flow of energy takes place in only one direction i.e. from producers to final consumers.
The energy present in one trophic level never returns back to the producer.

Energy flow in our ecosystem:

Net primary productivity (NPP) is equal to Gross primary productivity (GPP) minus Respiration loss (R). NPP is the available biomass for the consumption of heterotrophs in the ecosystem.

• Phytoplanktons are small floating photosynthetic unicellular plant.
• In the aquatic ecosystem phytoplankton are producers that fix solar energy by the process of photosynthesis.

Aquatic Food Chain:

The term ecosystem was first used in 1935 in a publication by British ecologist Arthur Tansley. Tansley devised the concept to draw attention to the importance of transfers of materials between organisms and their environment.

Pyramid of energy is always erect and upright because the amount of energy get reduce at each trophic level from prouder to consumers.

Ecological parameter includes, biomass, energy and number of individual in the ecosystem. Stratification is not a part of ecological parameter.

Primary productivity is the amount of biomass produced per unit area by green plants in an ecosystem. Producers fix the solar energy by the process of photosynthesis.

Ecosystem is the functional and dynamic unit of nature where living and non-living components interact with each other for flow of energy and biomass from producer to consumers.

Decomposition is the process that involves the breakdown of complex organic matter or biomass from the body of dead plants and animals with the help of decomposers into inorganic raw materials such as carbon dioxide, water, and other nutrients.

The various processes involved in decomposition are as follows:
➢ Fragmentation 

• It is the first step in the process of decomposition.
• It involves the breakdown of detritus into smaller pieces by the action of detritivores such as earthworms.

➢ Leaching

• It is a process where the water soluble nutrients go down into the soil layers and get locked as unavailable salts.

➢ Catabolism

• It is a process in which bacteria and fungi degrade detritus through various enzymes into smaller pieces.

➢ Humification

• The next step is humification which leads to the formation of a dark-coloured colloidal substance called humus, which acts as reservoir of nutrients for plants.

➢ Mineralization

• The humus is further degraded by the action of microbes, which finally leads to the release of inorganic nutrients into the soil.
• This process of releasing inorganic nutrients from the humus is known as mineralization.

The pyramid of biomass in an aquatic system is always inverted. A sharp decrease in biomass results in inverted pyramids.

Option A: Mineralization is the process in which humus is further degraded by some microbes and release of inorganic nutrients occur.

Option B: The degradation of the detritus into simple inorganic substances, by bacterial and fungal enzymes, is known as catabolism.

Option C: If the breakdown of the detritus by detrivores is called fragmentation.

Option D: Leaching is the process by which the water-insoluble inorganic nutrients go down into soil horizon and get precipitated as unavailable salts.

Hence,option B is correct.

• At a constant temperature, soil moisture content shows a parabolic affect on decomposition rates with a maximum rate at intermediate levels of moisture.
• High moisture content limits soil gas exchange leading to low oxygen concentrations and potentially anaerobic conditions.
• At low moisture content, the lack of water limits microbial metabolism; however, many microorganisms can remain active to much lower soil water potentials (at -3.0 MPa) than plants (at -1.5 MPa).

In a food chain, energy stored at the producer level is called as primary productivity (PP). Net primary productivity (NPP) is the rate of storage of organic matter except which is utilized for the respiration by plants.

In detritus food chain, speed of decomposition will be fast if detritus is rich in simple sugar that can be easily decomposed into glucose by saprophytes that includes bacteria and fungi.

Humus is a dark brown, amorphous, gummy substance that is formed when plant and animal matter partially decomposes. It is a reservoir of nutrients and is good for plant growth. Humus is resistant to microbial action and decomposes very slowly. However, some microbes further degrade humus, releasing inorganic nutrients through a process called mineralization.

Ecosystem services include all activities performed by nature to benefits human beings.

The most important ecological service includes soil formation. Soil is essential for the growth of plants that provide food to all living forms.

• Forests helps in producing rainfall. More are the trees, the more water gets absorbed into clouds and the more it helps in rain falls. 
• The roots of a tree make gaps in the soil so that when it rains the water can sink in before being absorbed by the soil.
• These spaces also allow air and water to reach the roots of the plants.  
• If the forests disappear, there will be less rain resulting in dryer conditions, that eventually lead to drought.
• Once this happens, the damage is extensive making it difficult to plant more trees or plants later because the soil is so hard and dry. When trees removed using heavy machinery, the soil is pushed down and the gaps fill in.
• Because all plants and trees need that water and air to reach roots, the conditions become unfriendly for new growth.

The components of the ecosystem are seen to function as a unit when you consider the following aspects:
(i) Productivity;
(ii) Decomposition;
(iii) Energy flow; and
(iv) Nutrient cycling.
 

- Assertion Evaluation: The assertion is true because nutrient cycling indeed comprises both gaseous (e.g., carbon cycle) and sedimentary (e.g., phosphorus cycle) types, and both are essential for maintaining ecosystem stability.

- Reason Evaluation: The reason is also true as it accurately describes the reservoirs for both cycles; however, it does not explain why both cycles are crucial for ecosystem health or how they interact.

- Conclusion: Since both the assertion and reason are true but the reason does not serve as the correct explanation for the assertion, the correct answer is Option B.

Detritivores play a crucial role in the decomposition process by breaking down organic matter into smaller particles, which facilitates further decomposition by microorganisms.