The question asks for the definition of 'standing crop' in an ecosystem. This is a fundamental concept in ecology, referring to the amount of living organic matter present at a specific point in time.
Correct Option: A) Total biomass of organisms at a given time
In ecology, the standing crop is the total amount of living organic matter (biomass) present in an ecosystem or a specific trophic level at a particular time. It is usually expressed as mass per unit area or volume (e.g., kg/m² or g/m³).
The question asks to identify the ecological term that results from subtracting respiration from Gross Primary Productivity (GPP). This is a fundamental concept in ecology related to energy flow and productivity in ecosystems.
This equation directly matches the description in the question.
B) Net Primary Productivity (NPP) — NPP is the amount of energy stored by producers after accounting for their own metabolic needs (respiration). It represents the biomass available for consumers.
The question asks to identify a decomposer from the given options. Decomposers are organisms that break down dead organic matter, returning nutrients to the ecosystem. We need to classify each option based on its role in the food chain.
C) Fungi are organisms that obtain nutrients by breaking down dead organic matter, such as dead plants and animals. They play a vital role in nutrient cycling by returning essential elements to the soil and atmosphere, making them decomposers.
The question asks to identify which biogeochemical cycle is NOT a gaseous cycle. Biogeochemical cycles describe the movement of chemical elements through the biological and geological components of the Earth. These cycles are broadly classified into gaseous cycles and sedimentary cycles based on where the primary reservoir of the element is found.
Correct Option: C) Phosphorus cycle is primarily a sedimentary cycle, meaning its main reservoir is in rocks and sediments, not in the atmosphere.
The question asks to identify the process by which atmospheric nitrogen is converted into ammonia by microorganisms. This is a fundamental concept in the nitrogen cycle, a crucial biogeochemical cycle.
B) Nitrogen fixation is the process by which atmospheric nitrogen (\(\text{N}_2\)) is converted into ammonia (\(\text{NH}_3\)) by microorganisms, making it available for use by plants and other organisms.
The question asks to identify the bacterium that forms root nodules in leguminous plants. This is a common biological association crucial for nitrogen fixation. We need to recall the specific bacteria known for this symbiotic relationship.
A) Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitrogen-fixing association with roots of legumes and other nitrogen-fixing plants. The bacteria colonize plant cells within root nodules, where they convert atmospheric nitrogen into ammonia for the plant, and in return, the plant provides the bacteria with carbohydrates.