Revision: Environmental Science Science SSLC (English Medium) Class 9 Tamil Nadu Board of Secondary Education

The circular movement of nutrients between living organisms and the physical environment of an ecosystem is called biogeochemical cycle.

Adaptation is a characteristic of the organism that enables it to survive and reproduce in its habitat. This characteristic can be morphological, physiological, or behavioural.

Water is obtained naturally from ice sheets, ice caps, glaciers, icebergs, ponds, lakes, rivers, streams, and underground is called freshwater.

The collection of rainwater for direct use or for recharging the groundwater level for indirect use is called water harvesting.

Environmental science is defined as the study of patterns, and processes in the natural world, and their modifications by human activities.

• Meaning → Movement of nutrient elements through the various components of an ecosystem is called Nutrient Cycling or Biogeochemical Cycles.
• Two Types → Nutrient cycles are of two types — Gaseous and Sedimentary.
• Gaseous Cycle → Reservoir is the atmosphere. Examples: Nitrogen cycle and Carbon cycle.
• Sedimentary Cycle → Reservoir is the Earth's crust. Examples: Sulphur cycle and Phosphorus cycle.
• Importance → Nutrient cycling ensures the continuous recycling of nutrients between the biotic (living) and abiotic (non-living) components of an ecosystem, unlike energy, which flows unidirectionally.

• Carbon is a key element of living organisms and is found in air, water, soil, rocks, and oceans (major reservoirs).
• The carbon cycle is the movement of carbon between the atmosphere, organisms, and the Earth through natural processes.
• Photosynthesis fixes CO₂ into organic matter, which passes through food chains.
• CO₂ returns to the atmosphere through respiration, decomposition, and combustion.
• Carbon sinks & humans: Fossil fuels and rocks store carbon, but human activities increase CO₂, causing global warming.