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Ecological Level
Transformation of biomass and energy through food webs

Autotrophs produce reduced carbon compounds from CO2 and water as energy sources and building materials.  The reduced carbon compounds are passed along food webs as one organism consumes another.  When the reduced carbon compounds are used as energy sources CO2 is often released.

Most autotrophs convert sunlight to chemical potential energy in reduced carbon compounds.  The reduced carbon compounds are used as energy sources and building materials by all organisms.

Carbon dioxide in the atmosphere is reduced and enters the biosphere through the process of photosynthesis and is oxidized and returned to the atmosphere through the process of cellular respiration.  Reduced carbon compounds move between organisms in a food web.

Organismal Level
Using Food for Energy

Carbon dioxide and water from the environment provide the building blocks for the synthesis of reduced carbon compounds via the process of photosynthesis.  The initial products of photosynthesis are sugars which can be made into other molecules through chemical reactions with the addition of other elements such as N, P, K, and S as needed.  Oxygen and water are byproducts of photosynthesis that leave the organism.

Photosynthetic organisms transform the light energy from the sun into chemical potential energy stored in the bonds of carbohydrates.

Carbohydrates are made in cells with photosynthetic pigments. Carbohydrates are transported throughout the plant where they provide the building blocks for other compounds.

Cellular Level

6CO2 + 12H2O -->

C6H12O6 + 6O2 + 6H2O

Light energy (photons) is transformed into Chemical potential energy (CPE) in the C-C and C-H bonds in reduced carbon compounds (sugar (CH2O)n). 

Occurs entirely within the chloroplasts of a cell.

Sub-cellular Level
Light-Dependent Reactions

12H2O + 12ADP + 12Pi + 12NADP+  -->           

 6O2 + 12ATP + 12NADPH + 12H+


Light energy (photons) --> CPE in proton gradient --> CPE in ATP

Light energy (photons) --> CPE in NADPH

Occurs in membranes (thylakoid membranes) facing the inside of the chloroplast’s grana.

Calvin Cycle (Light-Independent Reactions)

3CO2 + 9ATP + 6NADPH +6H+ --> (3-carbon sugar phosphate) C3H5O3Pi + 3H2O + 9ADP + 8 Pi + 6NADP+ 

CPE in bonds of ATP & NADPH --> CPE in the C-C and C-H bonds in  reduced carbon compounds.

Occurs in the stroma (fluid portion) of the chloroplasts.

Hexose and Other Molecule Production

(3-carbon sugar phosphates) 2C3H5O3Pi --> (6-carbon sugar phosphate) C6H11O6Pi + Pi

3- & 6-carbon sugars made into other building blocks with addition of N, S, and P as needed

CPE in stored in the C-C and C-H bonds

Much synthesis of macromolecules is coupled to the use of ATP.

Occurs in the cytosol.