Nutrient Cycles: Nitrogen and Phosphorus Explained

Saprobiont

A microorganism that feeds on the remains of dead plants and animals, using extracellular digestion to break down the remains.

Mycorrhizae

A symbiotic relationship between a fungus and the roots of a plant.

Extracellular digestion

When food is broken down (digested) outside of a cell. The cell releases the enzymes required to do this e.g., saprobionts.

Nitrogen fixation

The process in which nitrogen gas in the atmosphere is converted into nitrogen containing compounds, such as ammonia, by nitrogen-fixing bacteria.

Symbiotic relationship

When two species live closely and one or both species depends on the other for survival.

Mutualistic relationship

A type of symbiotic relationship where both species benefit.

Ammonification

The process in which nitrogen compounds from dead organisms or waste material, e.g., proteins, are turned into ammonium compounds by saprobionts.

Nitrification

The process in which ammonia and ammonium ions in the soil are converted into nitrogen compounds (nitrites and nitrates) by nitrifying bacteria.

Denitrification

The process in which nitrates in the soil are converted into nitrogen gas by denitrifying bacteria.

Assimilate

The movement of digested molecules into cells where they are used to build bigger molecules.

Guano

Faeces excreted by sea birds that is high in phosphates.

Weathering

The breakdown of rocks by mechanical, chemical and biological processes.

Leaching

The process in which water-soluble compounds in the soil are washed away e.g., by rain.

Eutrophication

The process whereby nutrients build up in water, leading to algal bloom. This results in the death of plants and decomposition of dead plant matter causing oxygen content of the water to fall and thereby killing aquatic organisms such as fish.

Nitrogen Cycle

A cycle where living organisms require a source of nitrogen from which to manufacture proteins, nucleic acids and other nitrogen-containing compounds.

Active transport

The process by which plants absorb nitrate ions (NO3 -) from the soil.

Root nodules

Special swellings on the roots of plants called legumes where nitrogen-fixing bacteria live.

Nitrogenase

The enzyme that catalyses the reduction reaction converting nitrogen gas into ammonia (NH3).

Saprobiontic nutrition

The process by which saprobionts break down organic molecules into inorganic ions, allowing for recycling.

Nitrifying bacteria

Bacteria that transform ammonium ions into nitrates through oxidation reactions.

Aerobic nitrifying bacteria

Bacteria that require oxygen to carry out the conversion of ammonium ions to nitrates.

Anaerobic denitrifying bacteria

Bacteria that convert soil nitrates into gaseous nitrogen when soils become waterlogged and have a low oxygen concentration.

Phosphorus Cycle

The cycle in which phosphorus, an important biological element, is constantly recycled as it is a component of ATP, phospholipids and nucleic acids.

Phosphate Ions

Chemical form of phosphorus, PO4 3-, in nature.

Sedimentary Rock Deposits

Main reservoir of phosphorus in the cycle.

Aquatic Producers

Organisms like algae absorbing phosphate from water.

Food Chain

Pathway through which phosphate moves via consumption.

Saprobionts

Decomposers releasing phosphate from dead organisms.

Algal Bloom

Rapid algal growth due to excess nutrients.

Natural Fertilisers

Organic materials like manure enhancing soil nutrients.

Artificial Fertilisers

Inorganic compounds mined and processed for crops.

Nitrogen

Essential element for plant growth and protein.

Species Diversity

Variety of species affected by nitrogen-rich soils.

Oxygen Depletion

Reduced oxygen levels harming aquatic life.

Anaerobic Organisms

Organisms thriving in low-oxygen environments.

Aerobic Respiration

Oxygen-dependent process for energy production.

Organic Manures

Natural fertilisers from decomposed plant and animal matter.

Nitrate Ions

Soluble nutrients leached from soil into water.

Drought Resistance

Ability of plants to withstand dry conditions.

Limiting Factor

Nutrient shortage restricting plant growth.

Biomass

Total mass of living organisms in an area.

Toxic Wastes

Harmful byproducts released by anaerobic organisms.

Nutrient Cycling

Movement and transformation of nutrients in ecosystems.