Cellular Respiration

The idea

Respiration is photosynthesis run backwards. Cells take the sugar and the oxygen and release the stored energy in a form the cell can spend.

$$\mathrm{C}{}_6\mathrm{H}{}_{12}\mathrm{O}{}_6+6\mathrm{O}{}_2\to 6\mathrm{CO}{}_2+6\mathrm{H}{}_2\mathrm{O}+\mathrm{energy}$$

Compare the two

	Photosynthesis	Cellular respiration
Who does it	Producers	Every living thing, producers included
Energy	Stored	Released
Takes in	$\mathrm{CO}{}_2$, $\mathrm{H}{}_2\mathrm{O}$	$\mathrm{C}{}_6\mathrm{H}{}_{12}\mathrm{O}{}_6$, $\mathrm{O}{}_2$
Gives off	$\mathrm{C}{}_6\mathrm{H}{}_{12}\mathrm{O}{}_6$, $\mathrm{O}{}_2$	$\mathrm{CO}{}_2$, $\mathrm{H}{}_2\mathrm{O}$
When	Only in light	All the time

graph LR
    subgraph Photosynthesis
        A["CO2 + H2O"] -->|light| B["glucose + O2"]
    end
    subgraph Respiration
        B --> C["CO2 + H2O + usable energy"]
    end
    C -.->|"the same molecules, going around again"| A

The pairing is the point

The outputs of one are the inputs of the other. That is what keeps the composition of the atmosphere roughly steady — and it is the clearest example of dynamic equilibrium you will meet all year.

Curriculum connection

B2.3

compare and contrast the processes of cellular respiration and photosynthesis, and explain how their complementary relationship contributes to the dynamic equilibrium of ecosystems

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B2.2

explain how naturally occurring phenomena, including the cycling of matter and the flow of energy, contribute to the dynamic equilibrium within and between ecosystems

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