NCERT Solutions for Class 12 Biology Chapter 12 Ecosystem

Short Note:

• An ecosystem consists of biotic (living organisms) and abiotic (physical/chemical) components interacting together, and is structured into producers (autotrophs, mainly green plants), consumers (herbivores, carnivores, omnivores) and decomposers (fungi and bacteria that break down organic matter).

• Primary productivity refers to the amount of biomass or organic matter produced by producers per unit area over a period of time, divided into Gross Primary Productivity (GPP, total production) and Net Primary Productivity (NPP, production remaining after respiratory losses).

Short Note:

• Decomposition is the process by which decomposers break down complex organic matter (detritus) present in dead plant and animal remains into simpler inorganic substances, occurring through the steps of fragmentation, leaching, catabolism, humification and mineralisation.

• The rate of decomposition is influenced by the chemical composition of detritus and climatic factors such as temperature and soil moisture, with warm, moist conditions generally favouring faster decomposition.

Short Note:

• Energy flow in an ecosystem is unidirectional, moving from producers to various levels of consumers, and follows the 10 per cent law, meaning only about 10% of energy is transferred from one trophic level to the next, with the rest lost mainly as heat during metabolic processes.

• Ecological pyramids represent the trophic structure of an ecosystem and can depict number, biomass, or energy at each trophic level; the pyramid of energy is always upright, while pyramids of number and biomass can sometimes be inverted (e.g. pyramid of numbers in a tree ecosystem).

Short Note:

• Biogeochemical cycles, such as the carbon cycle and phosphorus cycle, describe the continuous circulation of essential nutrients between living organisms and the abiotic environment.

• The carbon cycle primarily involves the exchange of carbon dioxide between the atmosphere and living organisms through photosynthesis and respiration, while the phosphorus cycle, lacking a significant atmospheric component, mainly involves the weathering of rocks as the primary source of phosphorus.