(a) What is an ecosystem? List its two main components. (b) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Explain.

(a) Ecosystem: All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.

Its two main components are:

1. Biotic components: Comprising living organisms such as plants, animals, and microorganisms (producers, consumers, and decomposers).
2. Abiotic components: Comprising physical factors like temperature, rainfall, wind, soil, and minerals.

(b) Cleaning of Aquarium vs. Ponds/Lakes:

• Ponds and lakes are natural, self-sustaining ecosystems. They contain a balanced community of producers, consumers, and decomposers (bacteria and fungi). The decomposers naturally break down dead organic matter and metabolic wastes into simple inorganic substances, which are reused by plants, thereby keeping the water clean.
• An aquarium is a human-made (artificial) and incomplete ecosystem. It lacks a balanced and sufficient population of decomposers and a complete food web. Consequently, dead remains of plants/fish and metabolic wastes accumulate and make the water toxic, requiring regular manual cleaning and water changes.