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Respiration

Respiration
Ecological Level
Transformation of biomass and energy through food webs

Autotrophs produce reduced carbon compounds from CO2 and water. The reduced carbon compounds are used as energy sources and building materials.  They are passed along food webs as one organism consumes another (red arrows).  When the reduced carbon compounds are used as energy sources, they are oxidized and typically CO2 is released. When the reduced carbon compounds become part of the biomass of the organism, they are available for the next trophic level.

Photo-autotrophs convert sunlight to chemical potential energy (CPE) in reduced carbon compounds.  The reduced carbon compounds are used as energy sources and building materials by all organisms.  The reduced carbon compounds are passed through food webs as one organism consumes another.  When the reduced carbon compounds become part of the biomass of the organism, their CPE is available for the next trophic level.

Carbon compounds are exchanged between organisms in a food web.

Organismal Level
Using Food for Energy

Food (reduced carbon compounds) provides molecules that serve as energy sources and building material for all organisms.  Some of the matter in food leaves aerobic organisms in the form of carbon dioxide and water.

Organisms transform the chemical potential energy (CPE) in food (reduced carbon compounds) into usable CPE in the reduced forms of energy management molecules such as ATP which powers cellular work and ultimately ends up as heat.

The cells of all organisms use food to build biomass and meet energy requirements.

Cellular Level
Cellular Respiration

C6H12O6 + 6H2O + 6O2 → 6CO2 + 12H2O

Some chemical potential energy (CPE) in reduced carbon compounds (carbon compounds with C-C and C-H bonds).

The multiple reactions involved in cellular respiration take place within the cell and require specialized membrane structures so that a proton gradient can be established.  The ATP made in the cell stays in the cell.

Sub-cellular Level
Glycolysis

C6H12O6 + 2ADP + 2Pi + 2NAD+

2C3H4O3 + 2ATP + 2NADH + 2H+

Some chemical potential energy (CPE) in reduced carbon compounds such as glucose ⇨ CPE in the reduced forms of energy management molecules (ATP, NADH + H+)

Glycolysis occurs in the cytoplasm in all living cells.
ATP is used in the cell where it is made.

Pyruvate Oxidation

2C3H4O3 + 2HSCoA + 2NAD+

2CH3COSCoA + 2CO2 + 2NADH + 2H+

Some chemical potential energy (CPE) in reduced carbon compounds such as glucose ⇨ CPE in the reduced forms of energy management molecules (ATP, NADH + H+)

Pyruvate Oxidation

Kreb's Cycle

2CH3COSCoA + 6H2O + 2ADP + 2Pi + 6NAD+ + 2FAD

4CO2 + 2HSCoA + 2ATP + 6NADH + 6H+ + 2FADH2

Some chemical potential energy (CPE) in reduced carbon compounds such as glucose ⇨ CPE in the reduced forms of energy management molecules (ATP, NADH + H+).

Electron Transport Chain & Oxidative Phosphorylation

10NADH + 10H+ + 2FADH2 + 6O2 + 34ADP + 34Pi

10NAD+ + 2FAD + 12H2O + 34ATP
(No carbon skeleton)

Some chemical potential energy (CPE) in reduced carbon compounds such as glucose ⇨ CPE in the reduced forms of energy management molecules (ATP, NADH + H+).

Electron transport chain

Respiration beyond sugars

Any reduced carbon compound can potentially enter respiration after removal of N,S, and P atoms and transformation into one of the intermediate molecules of respiration.

Any reduced carbon compound can potentially enter respiration and thus be used to meet energy needs.

Cells recycle reduced carbon compounds, building them into different molecules as needed.  However, once the carbon is completely oxidized to carbon dioxide it is released from the cell and can only be reused eventually by photosynthetic organisms.