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CELL ENERGETICS
Photosynthesis and Cellular Respiration
Photosynthesis
 All energy for Earth is from the sun.
 Photoautotrophs- organisms that convert light
energy to chemical energy.
 This process is called photosynthesis and is
summarized in the equation:
light energy
6H2O + 6CO2
6O2+ C6H12O6
Photosynthesis
 Occurs in chloroplasts of plant cells
2 sets of reactions
 Light dependent reactions
 occur in thylakoid- flattened membrane sac
 use water and light energy
 Produce Oxygen
 Light independent reactions
 occur in stroma
 use carbon dioxide
 produce Carbohydrates.
Light Dependent Reactions
 Sunlight strikes chlorophyll molecules
activating them
 Photolysis- occurs when the energy of sunlight
splits water molecules
 Oxygen atoms are released as O2
 Hydrogen atoms are stripped of their electrons
 The electrons pass to the electron carrier NADP+
forming NADPH and H+.
 H+ forms a concentration gradient
 The concentration gradient drives ATP Synthase
to make ATP
Light Independent Reactions
Light Independent Reactions
 CO2, ATP, and electrons carried by NADP+ are used
to build sugar.
 The molecule RuBP rearranges CO2 making the
molecule PGA .
 PGA is converted to PGAL, using ATP and the NADP+.
 Some PGAL is made into glucose; some regenerates
RuBP to continue the process.
Photosynthesis
CO2
Water
ADP + Pi
+ NADP+
RuBP
PGAL
ATP + NADPH
+ H+
Light Independent
Light Dependent
Reactions
Reactions
O2
Carbohydrates
Cellular Respiration
 Both autotrophs and heterotrophs must
convert glucose to ATP (the energy currency of
the cell) first, then use it to drive any metabolic
activity.
 This process is cellular respiration and is
summarized in the equation:
C6H12O6 + 6O2
6H2O + 6CO2 + ATP
 Aerobic organisms use cellular respiration
 Aerobic = oxygen using
Cellular Respiration
 Occurs in cytoplasm & mitochondria of eukaryote cells
3 sets of reactions
 Glycolysis occurs in cytoplasm
 breaks down glucose to pyruvate
 produces 2 molecules of ATP.
 Kreb’s Cycle occurs in matrix of mitochondria
 breaks down pyruvate
 produces CO2 and 2 molecules of ATP.
 Oxidative phosphorylation occurs in mitochondrial
matrix
 uses oxygen
 produces 32 molecules of ATP.
Glycolysis
 Glycolysis breaks down glucose (6-carbon sugar)
into 2 molecules of pyruvate (3-carbon
intermediate)
 some hydrogen atoms are stripped of electrons,
 electrons are passed to the carrier NAD+,
forming NADH and H+
 Glycolysis uses 2 ATP to rearrange glucose
 produces 4 ATP
 net total of 2 ATP are made by glycolysis
Kreb’s Cycle
 Pyruvate changes into Acetyl-Coenzyme A in the
cytoplasm
 Acetyl-CoA moves to the mitochondrial matrix,
 In a series of reactions
 carbon and oxygen molecules are pulled off to release
CO2
 electrons are passed to NAD+ and FAD
 forms NADH and FADH2 and many H+ ions.
 produces 2 molecules of ATP each time the cycle runs
Oxidative Phosphorylation
 Only NADH and FADH2 and H+ move into the
mitochondrial membrane
 Electrons from hydrogen pass through a
series of enzymes and finally to oxygen (the
electron acceptor) making O2
 As in light dependent reactions, H+ protons
develop a steep concentration gradient,
driving ATP synthase to produce ATP
 32 molecules of ATP are produced.
Cellular Respiration
Electrons carried
via NADH
GLYCOLYSIS
Glucose  Pyruvate
ATP
Electrons carried via
NADH and FADH2
KREB’S
CYCLE
ATP, CO2
O2
OXIDATIVE
PHOSPHORYLATION
ATP, H2O
Fermentation
 Aerobic cellular respiration occurs only when
Oxygen is present.
 Without oxygen, anaerobic respiration takes place.
 Glycolysis occurs.
 Fermentation- After glycolysis, pyruvate is
converted to lactic acid or ethanol
 Fermentation involves very few chemical
reactions,
 but only makes 2 molecules of ATP.