Test: Nutrient Cycling (NCERT) - NEET MCQ

The major reservoir pool of phosphate ios rocks and fossil bone deposits laid down in past. Phosphate is component of nucleic acids, biomembrances, etc., and body structures of shells, bones and teeth. Its cyling pool is soil for terrestrial system and water for aquatic system. Smalll amount of phosphate is added through weathering of rocks.

Biogeochemical cycles can be grouped into 3 types:
(i) Gaseous cycle: Material involved in circulation are gases or vapours and the reservoir pool is the atmosphere or hydrosphere, e.g., nitrogen, carbon, hydrogen, oxygen and water cycle.
(ii) Sedimentary cycle: Materials involved in circulation are non-gaseous and the reservoir pool is lithosphere, e.g., phosphorus, calcium and magnesium cycle.
(iii) Mixed cycle (materials involved in circulation have both gaseous and non-gaseous states) eg., sulphur cycle.

The cyclic movement of the elements from the abiotic system to the biotic system and back again is the biogeochemical cycle. These chemicals form the compounds of food, so these are also known as nutrient cycles. Some of the important biogeochemical cycles are carbon cycle, Oxygen cycle nitrogen cycle, Phosphorus cycle.
Following aspect are studied in biogeochemical cycling:

• The nature and size of the natural reservoir
• The rate of movement between reservoirs
• The interaction between different biogeochemical cycles

The flow chart represents phosphorus cycling in a terrestrial ecosystem because phosphorus cycle is a sedimentary cycle and its reservoir pool is lithosphere. Rocks are the natural reservoir of phosphorus, in the form of insoluble ferric and calcium phosphate. when rocks are weathered, minute amounts of these phosphates dissolve in soil solution and these inorganic phosphates (PO₄^3-,HPO₄^2-,or H₂PO₄) are absorbed by plants from the soil and water bodies and eventually pass into animals through food chains. There is no repiratory release of phosphorus. Gaseous exhcange of phosphorus between organisms and envirmonet are negligilbe.

Standing state is the amount of inorganic nutrients present anytime in the soil/water of ecosystem. Standing crop is the amount of living matter(or biomass) present in unit area of an ecosystem. Gaseous nutrient cycles are rapid and more perfect as compared to sedimentary nutrient cycles. It is because in gaseous cycles, nutrients remain in circulation more or less uniformly, whereas in sedimentary cycles, nutrients get out of circulation and constitute a relatively inactive, less perfect and immobile reservoir on earth's crust.

The cycling pool of carbon consists of 6 x 10¹⁴ kg (29%) of free CO₂ in the atmosphere, 1.45 x 10¹⁵ kg (71%) of dissolved CO₂ occurs in the oceans. Oceans also regulate the amount of CO₂ in the atmosphere.

Phosphorus has a sedimentary cycle of matter Its reservoir pool is phosphate rocks while cycling pool is terrestrial and aquatic ecosystems. Atmosphere or gaseous phase is absent.

Global water cycle consists of evaporation from water bodies (oceans, rivers, lakes etc.) and precipitation of water in the form of rain, snow and hail. Hence, water circulates between hydrosphere and atmosphere. It does not involve living organisms.

Evaporation from the oceans is the most important in water cycle, because it comprises of the major part of global water cycle.

Sulphur occurs in nature as an element and also as sulphates in soil, water and rocks. Major reservoir of sulphur is sulphate rocks. Soil and water also receive sulphates from rocks. Rainwater running over rocks gradually wears away their surface and carries off sulphur with it. Some of this sulphur soaks into the soil and some reaches ponds and lakes. A large part of sulphur is carried by the rivers to the sea where it may get locked up in sedimentary rocks. Wind may also erode the rocks, and the materials may be blown into the air as dust. Rain washes a significant amount of this matter from the atmosphere into the oceans.