Ecology & Ecosystems — Set 4

Correct Answer: D. Denitrification

Denitrification is carried out by bacteria like Pseudomonas in anaerobic conditions such as waterlogged soils. This process returns nitrogen to the atmosphere, completing the nitrogen cycle. It is a crucial step in preventing the excessive buildup of nitrates in terrestrial systems.

Correct Answer: C. Pyramid of Energy

The pyramid of energy shows the total amount of energy converted to biomass at each trophic level. It is measured in units like calories or joules per square meter per year. This pyramid provides the most accurate picture of the functional nature of an ecosystem.

Correct Answer: B. Unidirectional, Cyclic

The correct answer is 'Unidirectional, Cyclic'. Energy flows in one direction from producers to consumers and eventually dissipates as heat. Nutrients, however, circulate through the biotic and abiotic components in a repetitive cycle. This distinction is fundamental to understanding how ecosystems function over time.

Correct Answer: C. Presence of benthic macroinvertebrates

Benthic macroinvertebrates like stonefly nymphs are highly sensitive to changes in water quality and oxygen levels. Their presence or absence provides a biological record of pollution over time. They are widely used by environmentalists as reliable indicator species.

Correct Answer: B. Endemic Species

Endemic species are often found in isolated regions like islands or mountain ranges. For example, the Lion-tailed Macaque is endemic to the Western Ghats of India. Protecting their habitats is critical because they are more vulnerable to extinction.

Correct Answer: C. Nutrient enrichment (Nitrogen and Phosphorus)

Nutrient enrichment leads to a dense growth of plant life and algae, which can choke the water body. As these plants die and decay, they consume dissolved oxygen, harming fish and other aquatic life. This is often caused by runoff from agricultural lands or sewage discharge.

Correct Answer: B. Biodiversity

Biodiversity includes diversity within species (genetic), between species, and of ecosystems. High biodiversity is generally associated with more resilient and productive ecosystems. It provides essential services like pollination, pest control, and climate regulation.

Correct Answer: A. Raymond Lindeman

Raymond Lindeman introduced this law in 1942 while studying the energy dynamics of a cedar bog lake. It suggests that only about 10% of energy at one level is available to the next higher level. The rest is lost as heat or used for metabolic maintenance by the organisms.

Correct Answer: A. Standing Crop

Standing crop refers to the total weight or number of organisms per unit area at a specific moment. It is often measured as biomass (dry weight). This value provides a snapshot of the resources available to the next consumer level.

Correct Answer: B. Saprophytes

Saprophytes, primarily fungi and certain bacteria, use extracellular digestion to absorb nutrients from dead organic material. They play a vital role in cleaning the environment by decomposing waste. They are essential for returning inorganic minerals back to the geochemical cycle.