Aquatic Ecosystem

Oxygen on Earth mainly comes from photosynthesis, especially by phytoplankton (marine organisms), and oxygen levels differ between air and water.

Statement I is incorrect: * Oceans (phytoplankton) produce more oxygen than rainforests.

Statement II is correct: * Marine phytoplankton and photosynthetic bacteria produce about 50% of the world's oxygen.

Statement III is incorrect: * Atmospheric air has much more oxygen than surface water; water does not contain several folds higher oxygen than air.

So, the correct answer is: B

Statement 1 is Incorrect: Copepods are a group of small crustaceans found in nearly every freshwater and saltwater habitat; they are zooplankton that function as consumers (secondary producers) rather than primary producers. Statement 2 is Correct: Cyanobacteria are photosynthetic bacteria that obtain energy through photosynthesis and are significant primary producers in marine environments. Statement 3 is Correct: Diatoms are a major group of microalgae (phytoplankton) found in the oceans and are among the most important primary producers in the marine food chain. Statement 4 is Incorrect: Foraminifera are single-celled amoeboid protists that primarily function as consumers (zooplankton) by catching food with their ectoplasm.

* Filter feeders are a subgroup of suspension-feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialised filtering structure.

* Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish (including some sharks). Some birds, such as flamingos and certain species of duck, are also filter feeders. Filter feeders can play an important role in clarifying water, and are therefore considered ecosystem engineers. They are also important in bioaccumulation and, as a result, as indicator organisms. * Oyster is one of the filter feeders.

Pearl Farming - Pearls are the only gemstones in the world that come from a living creature. Mollusks such as oysters and mussels produce these precious jewels. - Pearl culture practices are present in Gujarat, Maharashtra, Bihar, Odisha, Kerala, Rajasthan, Jharkhand, Goa, and Tripura.

Biological Oxygen Demand (BOD) is a standard criterion for assessing the quality of water.

Microbial activity: BOD measures the amount of dissolved oxygen used by microorganisms (like bacteria) as they decompose organic matter in water.

Pollution indicator: Higher BOD indicates a greater presence of organic matter, often suggesting pollution from sources like sewage, animal waste, or decaying plants.

Aquatic life impact: Excessive organic matter decomposition can deplete oxygen levels in water, harming aquatic life that depends on dissolved oxygen for survival.

Therefore, BOD serves as a valuable tool for monitoring water quality and identifying potential pollution issues.


An ecosystem is a functional unit of nature where living organisms (biotic factors) interact among themselves and with their physical environment (abiotic factors) such as sunlight, water, and soil.

Key components of an ecosystem: 1. Biotic Components: Includes all living things like plants, animals, and microorganisms. 2. Abiotic Components: Includes non-living elements like air, water, soil, and sunlight. 3. Interdependence: It highlights the flow of energy and cycling of nutrients between the living and non-living components.

Analysis of Options: - Option A: Describes a 'community' (only interactions between living organisms). - Option B: Describes the 'biosphere' (the zone of Earth where life exists). - Option C: Correctly defines an ecosystem as the combination of the biotic community and its abiotic environment. - Option D: Refers to the 'biota' or 'biodiversity' of a specific region.

Diatoms: These are microscopic, single-celled algae that are primary producers in aquatic ecosystems. They use photosynthesis to convert sunlight, water, and carbon dioxide into organic matter (food).

Crustaceans: These are small aquatic animals like shrimp, crabs, and krill. They are primary consumers in the food chain and feed on diatoms and other phytoplankton (microscopic plants).

Herrings: These are small schooling fish that are secondary consumers in the food chain. They feed on crustaceans and other zooplankton (microscopic animals).

So, the energy flow starts with diatoms (producers) being eaten by crustaceans (consumers), which are then eaten by herrings (higher-level consumers).


Major reef formations in the Indian Seas occur in: - Gulf of Mannar, - Palk Bay, - Gulf of Kutch, - the Andaman and Nicobar Islands, and - Lakshadweep.


Coral reefs are marine ecosystems and cannot exist in the Sundarbans, which is a mangrove forest in the Ganges Delta and a brackish water ecosystem.