The circulation of elements or mineral nutrients from non-living to living and then back to non-living is called Biogeochemical cycling. Based on the nature of the reservoir, there are two types of cycles namely gaseous and sedimentary cycles.
Gaseous Cycle – where the reservoir is the atmosphere or the hydrosphere
Example: Carbon cycle, Water cycle, Nitrogen cycle etc.
Sedimentary Cycle – where the reservoir is the earth’s crust
Example: Phosphorus cycle, Sulphur cycle etc.

Volcanic eruptions emit water vapour and toxic gases into the atmosphere such as carbon dioxide, sulphur a. dioxide, hydrogen sulphide, hydrochloric acid and carbon monoxide Breathing (or respiration, or ventilation) is the process of moving air into and out of the lungs to facilitate gas exchange with the internal environment, mostly by bringing in oxygen and flushing out carbon dioxide.
Photosynthesis takes in the carbon dioxide produced by all breathing organisms and reintroduces oxygen into the atmosphere. Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms’ activities.
Decay of organic matter or putrefaction, process whereby heterotrophic organisms, including some bacteria, fungi, saprophytic plants, and lower animals, utilize the remains of once-living tissue as a source of nutrition. In the decomposition process, different products are released: carbon dioxide (CO2), energy, water, plant nutrients and re-synthesized organic carbon compounds.

Phosphorus cycle is mainly terrestrial. The main storage for phosphorus is in the earth’s crust. On land phosphorus is usually found in the form of phosphates.
It occurs in large amounts as a mineral in phosphate rocks and enters the cycle from erosion and mining activities. By the process of weathering and erosion phosphates enter rivers and streams that transport them to the ocean. In the ocean once the phosphorus accumulates on continental shelves in the form of insoluble deposits.
After millions of years, the crustal plates rise from the sea floor and expose the phosphates on land. After more time, weathering will release them from rock and the cycle’s geochemical phase begins again.
Statement 2: Being an important nutrient, phosphorous promotes eutrophication in lakes. Along with nitrogen related compounds it leads to undesirable situations like algal bloom.

Introduction of new species into the ecosystem often cause disruption in stability of ecosystem. For ex: Presence of alien species like lantana in tropical deciduous forest has resulted in frequent forest fires.

Alien species become ‘invasive’ when they are introduced deliberately or accidentally outside their natural areas, where they out-compete the native species and upset the ecological balance.
o Invasive animal species pose a threat to biodiversity and human well-being.
o Common characteristics of invasive species include:
Rapid reproduction and growth,
High dispersal ability,
Phenotypic plasticity (ability to adapt physiologically to new conditions), and
Ability to survive on various food types and in a wide range of environmental conditions.