The reason the remains and waste products of plants and animals do not accumulate on Earth is the work of tiny invisible organisms called decomposers. Let us learn how matter continuously cycles through ecosystems.
Basic Knowledge
Decomposers: Organisms that decompose the remains and waste products of plants and animals and return them to inorganic substances(carbon dioxide, water, and nitrogen compounds).
① Fungi(molds, mushrooms, yeast, and others): Multicellular organisms whose bodies are made of hyphae.
② Bacteria(lactic acid bacteria, Escherichia coli, cyanobacteria, and others): Unicellular prokaryotes(without a nucleus).
Decomposers are also a type of consumer(because they obtain energy by decomposing other organisms).
Carbon cycle:
① Plants take in atmospheric carbon dioxide through photosynthesis and convert it into organic matter.
② Animals eat plants and take organic matter into their bodies.
③ Through respiration, plants and animals break down organic matter and release CO₂.
④ Decomposers decompose the remains of plants and animals and release CO₂ and water.
In this way, carbon cycles between theatmosphere↔organisms.
Similarly, oxygen cycles, and water also cycles through evaporation, precipitation, water absorption, and transpiration.
Decomposer(An organism that decomposes the remains and waste products of plants and animals. Fungi and bacteria)
Fungi(Molds, mushrooms, and yeast. Reproduce by spores)
Bacteria(Bacteria. Unicellular prokaryotes without a nucleus)
Organic and inorganic substances(Compounds containing carbon = organic substances, those not containing carbon = inorganic substances)
Cycling of matter(The process by which carbon, oxygen, water, nitrogen, and other substances move through organisms and the environment)
Flow of energy(Energy flows from sunlight→producers→consumers and is lost as heat)
Further Exploration (Background and Significance)
Matter cycles, but energy does not cycle; it flows in one direction—this is an important principle of ecosystems.
Sunlight→photosynthesis by plants→animals→decomposers→heat(dispersed into the air)
At each stage, energy is consumed through respiration and eventually escapes into space as heat. Therefore, ecosystems need a constant supply of energy fromsunlight.
What would happen if there were no decomposers?—Fallen leaves, remains, feces, and other materials would continue to pile up on the ground, while inorganic substances(nitrogen and phosphorus) needed by plants would not be replenished, causing the entire ecosystem to collapse. It is believed that one gram of soil contains hundreds of millions to tens of billions of microorganisms, which support Earth.
Nitrogen cycle: Nitrogen makes up 78% of the air. Bacteria such as root nodule bacteria(which live symbiotically in the roots of legumes) convert it into forms that plants can use(ammonium ions and nitrate ions). This is called nitrogen fixation and provides the basis of fertilizer.
Distinguishing organic and inorganic substances: Compounds containing carbon(C) areorganic substances(starch, sugars, proteins, and lipids), while those not containing carbon areinorganic substances(water, carbon dioxide, oxygen, salts, and metals). However, CO₂ is an exception: although it contains carbon, it is treated as an inorganic substance.
- Decomposers = fungi(molds and mushrooms) and bacteria
- Decomposers break down organic substances→inorganic substances
- Carbon cycles between the atmosphere and organisms through photosynthesis, respiration, and decomposition
- Matter cycles, but energy flows in one direction(as heat is dissipated)
- The basic energy supporting ecosystems is sunlight
- Root nodule bacteria = live symbiotically with legumes and carry out nitrogen fixation
- Organic substances = contain carbon, inorganic substances = do not contain carbon(CO₂ is exceptionally treated as inorganic)
Points to Note (Often Confused)
① Fungi(molds and mushrooms, eukaryotic multicellular organisms) and bacteria(prokaryotic unicellular organisms) are different. ② Decomposers can also be classified as a type of consumer(they obtain nutrients by decomposing other organisms). ③ Matter cycles, while energy flows(and does not cycle). ④ Plants carry out respiration as well as photosynthesis(they respire continuously).
Practice
- State two groups of organisms that are decomposers.
- What is the process by which organisms convert carbon dioxide into organic matter in the carbon cycle?
- Between matter and energy, which cycles through an ecosystem?