Biology
Chapter 9 Notes
Chapter 9 Voc. Word list: ATP, photosynthesis, cellular respiration, chemosynthesis, nucleoside,
Light-dependent reaction, electron transport chain, photolysis, NADP, Light –independent reactions
(also called Dark reaction and Calvin cycle), Carbon fixation, RuBP, PGAL, anaerobic, aerobic,
Glycolysis, Citric Acid Cycle, acetyl-CoA, oxaloacetic acid, Citric acid, NAD, FAD, Alcoholic
fermentation, and Lactic fermentation
Section 9.1
All living things need energy for their cells.
 Without energy the cells would die.
 Organisms obtain energy from food.
 Plants and other green organisms (like algae and some bacteria) trap the light
energy from the sun and use it as needed in a process called photosynthesis.
 Some organisms (like some bacteria) obtain energy from chemicals in a
process called chemosynthesis.
 Animals eat their food to obtain energy.

The energy is stored in chemical bonds that eventually form adenosine triphosphate
(ATP) and the ATP is broken down as needed.
 The Adenosine is a nucleoside-purine protein part of a nucleic acid that has a
binding site for the phosphate groups (PO4-).
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Energy is needed to form the 1st AMP group bonds (Adenosine
monophosphate)
Additional energy is needed to form the 2nd step: AMP + P yields ADP
(Adenosine diphosphate)
More energy is needed to form the 3rd step: ADP + P yields ATP
As ATP is broken down it releases-ENERGY!
The formation/breakdown recycling activity of the ATP is important because it
relieves the cell from storing all the ATP it needs.
Section 9.2
Photosynthesis
Photosynthesis the process that involved the sun’s light energy is make simple sugars. It also uses
light energy to split water. Oxygen is produced when water is split.
Chemical Reaction: 6CO2 + 6H2O → (yield) C6H12O6 + 6O2
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The organelle in plant cells that places a vital role in photosynthesis is chloroplast.
 Chloroplasts are filled with a green pigment called chlorophyll.
 Chlorophyll and other pigments (the Thylakoid membranes contain the
pigments) in the chloroplasts are grouped into clusters. These clusters of
pigments trap light energy.
Two phases of photosynthesis
1. Light-dependent reactions convert light energy to chemical energy.
 This process requires the Sun’s light energy
 As the light strikes the chlorophyll molecules in the photosystem of the Thylakoid
membrane, the energy is transferred to electrons.
 The electrons are highly energized as they pass from the chlorophyll to an electron
transport chain-a series of proteins embedded in the Thylakoid membrane. The
electrons pass down the chain and release energy that
i. splits water →H+ and O2
 This part of the reactions is called photolysis
 The splitting of water must take place so photosynthesis can take
place over and over again.
 Without water photosynthesis will stop!
ii. forms NADP+ (carrier molecule of the electron transport chain called
nicotinamide adenine dinucleotide phosphate) NADP+ + H+→ NADPH (this
is stored as energy until it is transferred to the stroma)
iii. forms ATP (see section one again)
 see page 227 Figure 9.5 for a diagram
2. Light-independent reactions: Also called Calvin cycle and Dark reaction cycle because
no light is involved in the production of the simple sugars.
 A series of chemical reactions use Carbon dioxide to form simple sugars.
 The Calvin Cycle takes place in the stroma of the chloroplast
 See p. 229 for the Calvin cycle diagram
st
 1 : Carbon fixation occurs when it bonds to a 5-carbon sugar called ribulose
biphosphate (RuBP) to form an unstable 6-Carbon sugar.
 2nd: Then the unstable 6-Carbon sugar immediately forms two 3-Carbon sugars
 3rd: Then the ATP and the NADPH from the light reaction converts the 3-Carbon
sugars into phosphoglyceraldehyde (PGAL)
 4th: One out of 6 PGAL molecules is transferred to the cytoplasm and used in the
synthesis of sugars and other carbohydrates. (3 rounds of the cycle occur to produce
6 PGAL)
 5th: RuBP is replenished by 5 molecules of PGAL (each with 3 C atoms) reacting to
ATP to form the 5-Carbon sugar so the cycle can restart again.
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Section 9.3
Glucose is converted to ATP in the cytoplasm or mitochondria by the process called cellular
respiration.
 There are three stages involved in cellular respiration: glycolysis, the citric acid
cycle, and the electron transport chain
 The first stage, glycolysis, is anaerobic-no oxygen is required.
 The other two stages require oxygen so they are aerobic process.
Glycolysis
Glycolysis is a series of chemical reactions that breaks down glucose (6-Carbon sugar) into 2
pyruvic acid (3-Carbon molecule)
 Takes place in the cytoplasm of a cell
 Requires 2 ATP molecules to start the process
 Net Product: 2 ATP
 because the final product produces 4 ATP molecules
The Citric Acid Cycle
(Also called Krebs Cycle or Tricarboxylic Acid Cycle)
The Citric Acid Cycle is the first aerobic respiration which involves each glucose molecule to
produce 2 ATP molecules and H atoms.
 The Citric Acid Cycle occurs in the mitochondria.
 See p. 233 for the diagram
1st step: acetyl-CoA (two Carbon molecule) reacts with a 4-Carbon molecule called oxaloacetic acid
to form Citric acid-6-Carbon molecule.
2nd step: Formation of Carbon dioxide
 NAD+ (electron carrier) reacts with Citric acid and forms NADH + H+ and
produces CO2
 The citric acid molecule reduces to a 5-Carbon molecule
3rd step: Formation of a second CO2
 Again NAD+ reacts this time with the 5-Carbon molecule and forms NADH + H+
and produces CO2
 The 5-Carbon molecule reduces to a 4-Carbon molecule
4th step: The 4 –Carbon molecule goes through a series of reactions in which FADH2 (FAD is
flavin adenine dinucleotide-electron carrier). The carbon chain is rearranged, and the oxaloacetic
acid is formed again so the cycle can start over.
Product: 1 ATP, 2 CO2, 1 NAD, 1FAD, 3NADH, 3 H+ ions, and 1 FADH2
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Electron Transport Chain
Similar to electron transport formed in photosynthesis
2nd stage of aerobic respiration
Forms in the inner membrane of the mitochondrion
Starts with NADH and FADH2 from Citric Acid Cycle as they deliver energized
electrons at the top of the chain.
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The electrons are passed from protein to protein within the mitochondrion
membrane, slowly releasing energy as it goes down the chain.
 Some of the energy is used to make ATP and some used by an enzyme to
pump H+ ions into the center of the mitochondrion.
 Inner membrane of the mitochondrion is positive charged because of the high
concentration of H+ ions
 The exterior part of the mitochondrion layer becomes negatively charged
causing the H+ ions to be attracted there too.
 The final electron acceptor is oxygen, which reacts with four H+ ions and 4
electrons to form 2 molecules of water.
Overall Product: 36 ATP (32 here and 4 earlier) for every glucose molecule
Fermentation
Glycolysis forms pyruvic acid. If no oxygen is available (anaerobic) then the Citric Acid cycle does
not occur but fermentation will.
 Pyruvic acid has two possible anaerobic pathways
I.
II.
Alcoholic fermentation: Yeast and some plant cells contain enzymes that change
pyruvic acid into ethyl alcohol
 CO2 is produced but no additional ATP is produced
Lactic acid fermentation: Other cells, such as muscle cells, contain different enzymes
that change pyruvic acid to lactic acid.
 In this case, too much lactic acid causes muscle fatigue and pain.
 Often due to heavy exercising
 No additional ATP is produced
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