1. Pathways that Harvest and Store Chemical Energy6
Pathways that Harvest and Store Chemical Energy

2. Chapter 6 Pathways that Harvest and Store Chemical Energy
Key Concepts
6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy

3. Chapter 6 Pathways that Harvest and Store Chemical Energy
6.4 Catabolic and Anabolic Pathways Are Integrated
6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates

4. Chemical energy available to do work is termed free energy (G).
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Energy is stored in chemical bonds and can be released and transformed by metabolic pathways.
Chemical energy available to do work is termed free energy (G).
LINK Concept 2.5 reviews the principles of energy transformations

5. In cells, energy-transforming reactions are often coupled:
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
In cells, energy-transforming reactions are often coupled:
An energy-releasing (exergonic) reaction is coupled to an energy-requiring (endergonic) reaction.

6. Adenosine triphosphate (ATP) is a kind of “energy currency” in cells.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Adenosine triphosphate (ATP) is a kind of “energy currency” in cells.
Energy released by exergonic reactions is stored in the bonds of ATP.
When ATP is hydrolyzed, free energy is released to drive endergonic reactions.

7. Figure 6.1 The Concept of Coupling Reactions
Exergonic reactions release energy by breaking a P from an ATP molecule. some of the released energy is used to bind ADP to P ( an endergonic reaction), creating ATP. Endergonic reactions reuire energy, which is provided through the hydrolysis of ATP. This is an example of coupling reactions.

8. Figure 6.2 ATP

9. Hydrolysis of ATP is exergonic:
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Hydrolysis of ATP is exergonic:

10. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Free energy of the bond between phosphate groups is much higher than the energy of the O—H bond that forms after hydrolysis.
text art pg 102 here
(1st one, in left-hand column)
Phosphate groups are negatively charged, so energy is required to get them near enough to each other to make the covalent bonds in the ATP molecule.

11. Reduction is the gain of one or more electrons.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Energy can also be transferred by the transfer of electrons in oxidation–reduction, or redox reactions.
Reduction is the gain of one or more electrons.
• Oxidation is the loss of one or more electrons.
Transfer of hydrogen atoms involves transfer of electrons. So when a molecule loses a H, it is oxidized, when it gains a H, it is reduced.
(H = H+ + e–)
Although redox reactions involve the transfer of electrons, it is helpful to think of it in terms of the gain or loss of Hydrogen Atoms. Transfer of hydrogen atoms involves transfer of electrons.
The reduced molecule receives electrons or H+
The oxidized molecule loses electrons or Hydrogens

12. Oxidation and reduction always occur together.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Oxidation and reduction always occur together.
A at top has electrons, at bottom it does not. It has been oxidized (offloaded electrons).
B at top has no electrons at bottom it does. It has been reduced. (received).

13. Energy is transferred in a redox reaction.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
The more reduced a molecule is, the more energy is stored in its bonds.
Energy is transferred in a redox reaction.
Energy in the reducing agent is transferred to the reduced product.

14. Figure 6.3 Oxidation, Reduction, and Energy
You may notice the application of the highly reduced molecules as fuels.

15. Coenzyme NAD+ is a key electron carrier in redox reactions.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Coenzyme NAD+ is a key electron carrier in redox reactions.
NAD+ (oxidized form)
NADH (reduced form)
NAD = nicotinamide adenine dinucleotide.

16. Figure 6.4 A NAD+/NADH Is an Electron Carrier in Redox Reactions

17. Reduction of NAD+ is highly endergonic, storing energy.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Reduction of NAD+ is highly endergonic, storing energy.
Oxidation of NADH is highly exergonic, releasing energy.

18. Figure 6.4 B NAD+/NADH Is an Electron Carrier in Redox Reactions
AH is oxidized to A, as it loses its H. the H is taken up by the NAD+, which is reduced to NADH, an electron carrier molecule.
The NADH transfers its H to the B, which is reduced to BH. The oxidized NAD+ is formed.

19. • Energy for anabolic processes is supplied by ATP.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
In cells, energy is released in catabolism by oxidation and trapped by reduction of coenzymes such as NADH.
• Energy for anabolic processes is supplied by ATP. .
LINK Concept 2.5 reviews the principles of catabolism and anabolism

20. C6H12O6 + 6O2 >>>>6CO2 + 6H2O + energy
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
Cellular respiration is a major catabolic pathway. Glucose is oxidized:
C6H12O6 + 6O2 >>>>6CO2 + 6H2O + energy
(686kcal/molecule of glucose)
Photosynthesis is a major anabolic pathway. Light energy is converted to chemical energy:
6CO2 + 6H2O >>>>C6H12O6 + 6O2
LINK Concept 2.5 reviews the principles of catabolism and anabolism

21. Oxidation occurs in a series of small steps in three pathways:
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Cellular Respiration
A lot of energy is released when reduced molecules with many C—C and C—H bonds are fully oxidized to CO2.
Oxidation occurs in a series of small steps in three pathways:
1. glycolysis
2. pyruvate oxidation
3. citric acid cycle
4. ETC/ Oxidative phosphorylation.
All you need to know are the location, the reactants and products of each stage, and the net gain of ATP at each stage of the process. You should be aware of the source of each of the reactants and what becomes of each product.
You DO NOT need to know the enzymes or structures of the intermediaries

22. Figure 6.8 Energy Metabolism Occurs in Small Steps
It is thought that breaking glucose down over lots of small steps allows for the capture of greater amounts of energy.

23. Figure 6.9 Energy-Releasing Metabolic Pathways
All you need to know for each of the 3 stages is: the location, the reactants and products of each stage, and the net gain of ATP and by which process. You should be aware of the source of each of the reactants and what becomes of each product.
You DO NOT need to know the enzymes ir structures of the intermediaries

25. An overview of cellular respiration
An overview of cellular respiration
NADH
FADH2
GLYCOLYSIS
Glucose
Pyruvate
CITRIC ACID CYCLE
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Substrate-level phosphorylation
Oxidative phosphorylation
Mitochondrion
and
High-energy electrons carried by NADH
ATP
CO2
Cytoplasm
Figure 6.6

26. Glycolysis: ten reactions. Takes place in the cytosol. Final products:
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Glycolysis: ten reactions.
Takes place in the cytosol.
Final products:
2 molecules of pyruvate (pyruvic acid)
2 molecules of ATP
2 molecules of NADH

27. Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 1)
The first stage of glycolysis is energyinvesting, consuming ATP. The second stage of glycolysis is energy releasing, producing ATP and NADH

28. Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 2)
Fructose, a 6 carbon sugar gets split into two 3 carbon sugars (glyceraldehyde).

29. Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 3)
In the final stages of glycolysis, the 3 carbon sugars are oxidized, NAD+ is reduced, creating 2 molecules of pyruvate, NADH and Atp is produced. All told, glycolysis takes place over 10 enzyme catalyzed steps, which you do NOT need to know.

30. Products: CO2 and acetate; acetate is then bound to coenzyme A (CoA)
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Pyruvate Oxidation:
Products: CO2 and acetate; acetate is then bound to coenzyme A (CoA)
In this step, the 2 pyruvate molecules are oxidized, resulting in the reduction of NAD+ creating NADH, and the release of CO2. It is then bound to Coenzyme A (which is a acetyl carrier molecule). The main role of Acetyl Co A is to donate its acetyl group to a 4 carbon compound called oxaloacetate which is formed late in the citric acid cycle. When the acetyl CoA is added to the Oxaloacetate, Citrate is formed. Citrate initiates the Citric Acid cycle, which is responsible for harvesting ATP for most life forms.

31. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Citric Acid Cycle: 8 reactions, operates twice for every glucose molecule that enters glycolysis.
Starts with Acetyl CoA with its 2 carbons being combined with Oxaloacetate, a 4 carbon compound.
Oxaloacetate is regenerated in the last step, ensuring that the cycle can continue

32. Figure 6.11 The Citric Acid Cycle
Again, you don’t need to know all the steps. Starts with Acetyl CoA with its 2 carbons being combined with Oxaloacetate, a 4 carbon compound. Oxaloacetate is regenerated in the last step, ensuring that the cycle can continue
What is important is that CO2 is removed s a waste, 2 ATP. NADH and FADH are generated thru redox. They are highly energized electron carrier molecules, which are critical to initiating the ETC. This stage, while it doesnot directly receive an input of oxygen, is aerobic.

33. For each turn of the cycle Two CO2 molecules are released
The energy yield is one ATP, three NADH, and one FADH2
and
Steps
CITRIC ACID CYCLE
Oxaloacetate
CoA
2 carbons enter cycle
Acetyl CoA
Citrate
leaves cycle
+ H+
NAD+
NADH
CO2
Alpha-ketoglutarate
ADP P
ATP +
Succinate
FAD
FADH2
Malate
Step
Acetyl CoA stokes the furnace.
NADH, ATP, and CO2 are generated during redox reactions.
Redox reactions generate FADH2 and NADH.
Figure 6.9B 1 5
Again, you don’t need to know all the steps. What is important is that CO2 is removed s a waste, 2 ATP. NADH and FADH are generated thru redox. They are highly energized electron carrier molecules, which are critical to initiating the ETC. This stage, while it doesnot directly receive an input of oxygen, is aerobic. 2 4 3

34.
Citric acid cycle

35. ELECTRON TRANSPORT CHAIN, CHEMIOSMOSIS, AND OXIDATIVE PHOSPHORYLATION.

36. Electron transport/ATP Synthesis:
Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
Electron transport/ATP Synthesis:
NADH is reoxidized to NAD+ and O2 is reduced to H2O in a series of steps.
Respiratory chain—series of redox carrier proteins embedded in the inner mitochondrial membrane.
Electron transport—electrons from the oxidation of NADH and FADH2 pass from one carrier to the next in the chain.

37. Oxidative phosphorylation couples oxidation of NADH:
with production of ATP:
This is a fundamental piece of chemistry behind cellular respiration

38. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism
The coupling is chemiosmosis—diffusion of protons across a membrane, which drives the synthesis of ATP.
Chemiosmosis converts potential energy of a proton gradient across a membrane into the chemical energy in ATP.

39. Most ATP production occurs by oxidative phosphorylation
Electrons from NADH and FADH2
Travel down the electron transport chain to oxygen, which picks up H+ to form water
Energy released by the redox reactions
Is used to pump H+ into the space between the mitochondrial membranes

40. Figure 6.12 Electron Transport and ATP Synthesis in Mitochondria
Electrons from NADH and FADH2 Travel down the electron transport chain to oxygen, which picks up H+ to form water. That O2 molecule right there represents the oxygen we inhale when breathing. Its sole purpose here is to act as an electron (H+)acceptor is the reason we breath.
2H e O2 _____> H2O. The H2O we exhale.
Energy released by the redox reactions Is used to pump H+ into the space between the mitochondrial membranes creating a concentration gradient.

41. Figure 6.5 A Chemiosmosis
The puple is a proton pump, which pushes H+ ions aginst their concentration gradient, so that a proton gradient is created across the membrane.
The brown is ATP synthase, an enzyme that allows protons to pass through it, thus difusing into the cell or mitochondria. Each proton that passes through causes the enzyme to rotate, bonding ADP to a P, and ATP is formed.

42. Figure 6.5 B Chemiosmosis
ATP synthase—membrane protein with two subunits:
F0 is the H+ channel; potential energy of the proton gradient drives the H+ through.
F1 has active sites for ATP synthesis

43. http://bcs.whfreeman.com/webpub/Ektron/pol1e/Animated Tutorials/at0602/at_0602_e_trans_atp_syn.html
Electron transport chain.

44. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy
About 32 molecules of ATP are produced for each fully oxidized glucose.
APPLY THE CONCEPT Carbohydrate catabolism in the presence of oxygen releases a large amount of energy

45. Under anaerobic conditions, NADH is reoxidized by fermentation.
Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy
Under anaerobic conditions, NADH is reoxidized by fermentation.
There are many different types of fermentation, but all operate to regenerate NAD+.
The overall yield of ATP is only two—the ATP made in glycolysis.

46. Lactic acid fermentation: End product is lactic acid (lactate).
Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy
Lactic acid fermentation:
End product is lactic acid (lactate).
NADH is used to reduce pyruvate to lactic acid, thus regenerating NAD+.

47. Figure 6.13 A Fermentation
The Reduced NADH is used to convert pyruvate into lactic acid. The NADH is oxidised, regenerating NAD+, so that glycolysis can continue. The only ATP made is the 2 molecules from glycolysis.

48. Alcoholic fermentation: End product is ethyl alcohol (ethanol).
Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy
Alcoholic fermentation:
End product is ethyl alcohol (ethanol).
Pyruvate is converted to acetaldehyde, and CO2 is released. NADH is used to reduce acetaldehyde to ethanol, regenerating NAD+ for glycolysis.

49. Figure 6.13 B Fermentation
The Reduced NADH is used to convert pyruvate into ethanol. The NADH is oxidised, regenerating NAD+, so that glycolysis can continue. The only ATP made is the 2 molecules from glycolysis

50.
Glycolysis and fermentation.

51. Figure 6.14 Relationships among the Major Metabolic Pathways of the Cell
Catabolism:
Polysaccharides are hydrolyzed to glucose, which enter glycolysis.
Lipids break down to fatty acids and glycerol. Fatty acids can be converted to acetyl CoA.
Proteins are hydrolyzed to amino acids that can feed into glycolysis or the citric acid cycle

52. PHOTOSYNTHESIS
6CO2 + 6H2O >>>>C6H12O6 + 6O2

53. Figure 6.15 An Overview of Photosynthesis
The light reactions convert light energy into ATP and NADPH, a reduced electron carrier molecule.
The carbon fixation reactions do not use light directly (dark reactions). They use the ATP and NADPH created in the light reaction, along with CO2 to make carbohydrates.

54. Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Light is a form of electromagnetic radiation, which travels as a wave but also behaves as particles (photons).
Photons can be absorbed by a molecule, adding energy to the molecule—it moves to an excited state.

55. Figure 6.16 The Electromagnetic Spectrum
Longer wavelengths have less energy.

56. Pigments: molecules that absorb wavelengths in the visible spectrum.
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Pigments: molecules that absorb wavelengths in the visible spectrum.
Chlorophyll absorbs blue and red light; the remaining, reflected light is mostly green.
Absorption spectrum—plot of light energy absorbed against wavelength.
Action spectrum—plot of the biological activity of an organism against the wavelengths to which it is exposed

57. Figure 6.17 Absorption and Action Spectra
Absorption spectrum—plot of light energy absorbed against wavelength.
Action spectrum—plot of the biological activity of an organism against the wavelengths to which it is exposed

58. Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
In plants, two chlorophylls absorb light energy chlorophyll a and chlorophyll b.
Accessory pigments—absorb wavelengths between red and blue and transfer some of that energy to the chlorophylls.
VIDEO 6.1 A green alga, Pediastrum simplex

59. Chloroplast label quiz
Game : label a chloroplast

60. Figure 6.18 The Molecular Structure of Chlorophyll (Part 1)
The pigments (chlorophyll) are arranged into light-harvesting complexes (antennae systems),.
The image on the right is a photosystem. A photosystem spans the thylakoid membrane in the chloroplast; it consists of antenna systems and a reaction center

61. Figure 6.18 The Molecular Structure of Chlorophyll (Part 2)

62. Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
The pigments are arranged into light- harvesting complexes, or antenna systems.
A photosystem spans the thylakoid membrane in the chloroplast; it consists of antenna systems and a reaction center.

63. The acceptor molecule is reduced.
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
When chlorophyll (Chl) absorbs light, it enters an excited state (Chl*), then rapidly returns to ground state, releasing an excited electron.
Chl* gives the excited electron to an acceptor and becomes oxidized to Chl+.
The acceptor molecule is reduced.

64. Final electron acceptor is NADP+, which gets reduced:
Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
The electron acceptor is first in an electron transport system in the thylakoid membrane.
Final electron acceptor is NADP+, which gets reduced:
ATP is produced chemiosmotically during electron transport (photophosphorylation).
ANIMATED TUTORIAL 6.3 Photophosphorylation

65. Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Two photosystems:
Photosystem I absorbs light energy at 700 nm, passes an excited electron to NADP+, reducing it to NADPH.
• Photosystem II absorbs light energy at nm, produces ATP, and oxidizes water molecules.

66. Figure 6.19 Noncyclic Electron Transport Uses Two Photosystems
Photosystem II. A Chlorophyll in the thylakoid membrane absorbs a photon of light, becoming excited. It gives of an electron, to an adjacent chlorophyll in the same photosystem which becomes excited. It then gives off an electron to the next chlorophyl and so on. The energy eventually arrives at a ground state (un energized) chlorophyll in the reaction centre of the photosystem. It absorbs the energy, becoming excited and then gives off its excited electron to a CHEMICAL acceptor. The reaction cetre chlorophyll gets oxidized while the chemical acceptor gets reduced. The oxidized reaction centre chloroplast is now a strong oxidizing agent. It strips electrons from a water molecule, splitting the H-O-H bonds. Every 2 water molecules split will yield 1 molecule of O2, which is released to the atmosphere as waiste. Thus, the source of O2 produced in photosynthesis is the water taken in as a reactant.
The excited electron acceptor then passes the excited electrons along a series of acceptor proteins embedded in the thylakoid membrane. Each acceptor protein pushes a proton through to the inside, creating a gradient. ( Just like the respiratory chain in Cell respiration. The protons diffuse back through via ATP synthase, making ATP in the process.

67. Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Photosystem II
When Chl* gives up an electron, it is unstable and grabs an electron from another molecule, H2O, which splits the H—O—H bonds.
So photosystem 2 makes ATP and O2.

68. Figure 6.19 Noncyclic Electron Transport Uses Two Photosystems
Photosystem I
In photosystem 1 the reaction centre chlorophyll absorbs a photon, becoming excited, and gives up an electron, it grabs another electron from the end of the electron transport chain of Photosystem II. This electron ends up reducing NADP+ to NADPH. It is that electorn that the reaction centre chlorophyll grabs from the photosystem 2 ETC that links the 2 photosystems.

69. Concept 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy
Photosystem I
When Chl* gives up an electron, it grabs another electron from the end of the transport system of Photosystem II. This electron ends up reducing NADP+ to NADPH.
So photosystem1 makes NADPH, which, together with the ATP from PS2, will provide the energy for the Calvin cycle.

70. Tutorials/at0603/at_0603_photophosphorylat.html
PHOTOPHOSPHORYLATION

71. Each reaction is catalyzed by a specific enzyme.
Concept 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
The Calvin cycle: CO2 fixation. It occurs in the stroma of the chloroplast.
Each reaction is catalyzed by a specific enzyme.
ANIMATED TUTORIAL 6.5 Tracing the Pathway of CO2

72. Figure 6.21 The Calvin Cycle
To fix something means to take something useless (CO2) and build it into something energy rich (Glucose etc.)
1. Fixation of CO2:
CO2 is added to ribulose 1,5-bisphosphate (RuBP). RUBP is a 5 Carbon molecule that functions as a CO2 acceptor molecule.
Ribulose bisphosphate carboxylase/oxygenase (rubisco) catalyzes the reaction, but it works slowly.
A 6-carbon molecule results, which quickly breaks into two 3-carbon molecules: 3-phosphoglycerate (3PG).
2. 3PG is reduced to form glyceraldehyde 3-phosphate (G3P).
3. The CO2 acceptor, RuBP, is regenerated from G3P.
Some of the extra G3P is exported to the cytosol and is converted to hexoses (glucose and fructose).
When glucose accumulates, it is linked to form starch, a storage carbohydrate

73. http://bcs.whfreeman.com/webpub/Ektron/pol1e/Animated Tutorials/at0605/at_0605_pathway_co2.html
Calvin cycle animated tutorial

74. CO2 is added to ribulose 1,5-bisphosphate (RuBP).
Concept 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
1. Fixation of CO2:
CO2 is added to ribulose 1,5-bisphosphate (RuBP).
Ribulose bisphosphate carboxylase/oxygenase (rubisco) catalyzes the reaction.
A 6-carbon molecule results, which quickly breaks into two 3-carbon molecules: 3- phosphoglycerate (3PG).
VIDEO 6.2 Rubisco: A three-dimensional model

75. 2. 3PG is reduced to form glyceraldehyde 3- phosphate (G3P).
Concept 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
2. 3PG is reduced to form glyceraldehyde 3- phosphate (G3P).

76. 3. The CO2 acceptor, RuBP, is regenerated from G3P.
Concept 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
3. The CO2 acceptor, RuBP, is regenerated from G3P.
Some of the extra G3P is exported to the cytosol and is converted to hexoses (glucose and fructose).
When glucose accumulates, it is linked to form starch, a storage carbohydrate.

77. Concept 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates
The C—H bonds generated by the Calvin cycle provide almost all the energy for life on Earth.
Photosynthetic organisms (autotrophs) use most of this energy to support their own growth and reproduction.
Heterotrophs cannot photosynthesize and depend on autotrophs for chemical energy.
LINK Concept 45.3 The roles of autotrophs and heterotrophs in ecosystems are described