3.3.5 Nutrient cycles

Why must nutrients be continuously recycled in ecosystems?

Because nutrients exist in limited amounts on Earth – they are finite and must be reused between living organisms and the non-living environment.

Where are chemical elements like carbon, nitrogen, and phosphorus stored in living organisms?

In complex organic molecules such as proteins, nucleic acids, lipids, and carbohydrates.

Define saprobionts (saprophytes

Microorganisms (such as bacteria and fungi) that feed on dead organic matter and waste products, carrying out extracellular digestion.

What is extracellular digestion?

The secretion of enzymes outside the organism to break down complex organic polymers into simple inorganic molecules or ions.

What do saprobionts release back into the environment?

Simple inorganic ions and molecules such as NH₄⁺, NO₃⁻, and PO₄³⁻.

How do producers (plants/algae) obtain nutrients?

They take up simple inorganic ions/molecules from the abiotic environment (soil or water) through their roots or cell membranes.

What is assimilation in the context of nutrient cycling?

The incorporation of simple inorganic nutrients into new complex organic biological molecules (e.g., synthesising amino acids, ATP, or DNA).

How are nutrients passed along food chains?

Consumers eat producers (or other consumers), digest complex organic substances into smaller monomers, and assimilate them into their own organic tissues.

What happens to nutrients when organisms die or produce waste?

Saprobionts decompose the dead organic matter, releasing simple inorganic ions back into the environment for producers to take up again – completing the cycle.

What is the difference between digestion and assimilation?

Digestion is the breakdown of large organic molecules into smaller soluble molecules.
Assimilation is the absorption and incorporation of these small molecules into the organism's own tissues (building them into complex organic compounds).

What is saprobiotic nutrition?

Obtaining nutrients from dead organic matter and animal waste using extracellular digestion.

How do saprobionts carry out extracellular digestion?

They secrete digestive enzymes externally onto dead/waste material, breaking down complex organic polymers into simple inorganic molecules or ions.