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8.10. Matter cycle and energy flow

The cycle of matter and the flow of energy

In ecosystems two transfer processes take place:

  • Energy flow, open. Of the solar energy that reaches the Earth, most of it is reflected and absorbed by the atmosphere, the earth's surface and the seas. Only 2% of the solar energy that arrives is absorbed by plants and, from here, passes to the rest of living beings.
  • Cycle of matter, closed.

The organism producing, by photosynthesis, manufacture their own organic matter (carbohydrateslipidsproteins, etc.) from inorganic materials such as H2O, CO2, and mineral salts, using energy from the sun.

When a primary consumer feeds on a producer, or a secondary consumer feeds on a primary consumer, the energy contained in organic matter (carbohydrateslipidsproteins, etc.) and the chemical elements that make up those substances are transferred, from one trophic level to a higher one.

This is the cycle of matter and the flow of energy  in an ecosystem.

The cycle of matter

All ecosystems need matter and energy to function. Energy, once solar energy is transformed by producers into chemical energy by making organic matter in photosynthesis, is transmitted along with matter.

The matter passes from the producers to the rest of the trophic levels, up to the decomposers, which will be the ones that end up with the recycling of the matter. Inorganic molecules (water and mineral salts) and organic (carbohydrates, lipids, proteins, etc.) are transformed when passing from one beings to others, but the chemical elements that constitute them (carbon, nitrogen, phosphorus, etc.) continue being the same.

In this way, matter passes from the environment to living beings, and from these, it is returned to the environment forming a closed cycle. We could think of a large spaceship called "Earth" that has a certain matter, in the form of atoms, that are passed from one being to another. The excrement and remains of living beings serve as food for the decomposers, which transform these substances by recycling them so that they can be used again by the producing organisms. It is, therefore, a closed cycle.

Matter, in addition to circulating through living beings, also does so through the inert medium (earth, water and air).

Interactive Activity: Organic or Inorganic?.

Interactive activity: Where do these chemical elements come from?.

The flow of energy

The flow of energy, on the other hand, is a unidirectional and open cycle. The energy from the Sun is captured by photosynthetic autotrophic organisms (plants, algae and some bacteria) that use it to obtain organic matter (rich in chemical energy) from inorganic matter (poor in energy).

The chemical energy stored in the producing organisms passes, through food, to the primary consumers (herbivores) and, from these, to the secondary consumers (carnivores), and to successive trophic levels. Chemical energy passes from one level to another until it is dissipated as heat.

Flujo de la energía en un ecosistema

The flow of energy is therefore a unidirectional and open flowEnergy is not recycled as it happens with matter, it flows from the autotrophs to the heterotrophs until it dissipates in the middle.

Every time energy passes (with feeding) from one trophic level to another, energy is lost. The 10% rule says that, as a consequence of respiration and other processes, only 10% of the energy that reaches it is transferred from one trophic level to the next. This is the reason why food chains have a reduced number of links.

The causes of energy loss are due to:

  • Living things need energy to perform their vital functions. It dissipates as heat.
  • Waste is produced that passes to the decomposers, without this energy being used at that trophic level.