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Energy for Life
� Biochemical pathways � A series of reactions where the products of
one reaction is used in the next reaction
Light Absorption in Chloroplasts
� Chloroplasts � Two membranes � Grana- layered stacks of
thylakoids which contain chlorophyll
� There is a solution called the stroma which surrounds the grana
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Light Absorption in Chloroplasts
� Light and Pigments � Electromagnetic radiation ○ What is white light?
Light Absorption in Chloroplasts
� Pigments ○ A compound that absorbs certain wavelengths
and reflects others
� Chloroplast pigments � Thylakoids contain chlorophylls and
carotenoids � Two types of chlorophylls ○ Chlorophyll a absorbs more red ○ Chlorophyll b absorbs more blue
Light Absorption in Chloroplasts
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Electron Transport
� Photosystems � Clusters of chlorophylls and carotenoids � 2 types ○ Photosystem I ○ Photosystem II
� Reactions fueled by light start when pigments in both photosystems absorb light
Electron Transport
� The energy from light is transferred until it reaches chlorophyll a molecules
� 5 steps � Step 1- Light forces electrons to go to a
higher energy level in photosystem II � Step 2- Excited electron leaves chlorophyll a ○ Oxidation/Reduction reaction (OIL RIG) ○ A molecule called the primary electron
acceptor, found in the thylakoid membrane, takes electron
Electron Transport � Step 3- Primary electron acceptor passes
electron on to a group of molecules called the electron transport chain ○ As electron moves along chain, protons move
into the thylakoid � Step 4- Light is also absorbed at the same
time by photosystem I. ○ Electrons move from chlorophyll a to another
primary electron acceptor ○ Electron lost is replaced by electron from
photosystem II
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Electron Transport � Step 5- The primary electron acceptor of
photosystem I releases electron to a different electron transport chain which takes it to outside of thylakoid membrane that faces stroma ○ The electron then combines with NADP+ to
make NADPH
Electron Transport
Electron Transport
� Restoring Photosystem II � An enzyme inside the thylakoid splits water
to replace the missing electrons ○ 2H2O à 4H+ + 4e- + O2
� Proton stays inside thylakoid to be used later � Electrons are put into photosystem II � Oxygen diffuses out of chloroplast
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Chemiosmosis � Chemiosmosis is the
synthesis of ATP � A protein called ATP
synthase, located in the thylakoid membrane, uses the protons to change ADP to ATP
� It is like a dam letting water out turning turbines
� Protons flow from high concentration to low concentration
Calvin Cycle
� The carbon atoms released from CO2 during photosynthesis are bonded into organic compounds
� Through a series of steps the carbon is bonded to make compounds such as amino acids, lipids, and carbohydrates
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Glycolysis � The organic compounds produced by
plants will be broken down by heterotrophs to gain energy
� Glycolysis is the process of turning glucose into 2 pyruvic acid molecules � One NADH molecule is made per pyruvic acid
� Once pyruvic acid is produced there are two possible pathways � Anaerobic respiration � Aerobic respiration
Anaerobic Respiration
� Anaerobic respiration occurs when there is an absence of oxygen
� Anaerobic respiration is also known as fermentation
� There are two types of fermentation � Lactic acid fermentation � Ethyl alcohol fermentation
Anaerobic Respiration � Lactic Acid
Fermentation � An enzyme
converts pyruvic acid into lactic acid by taking two hydrogen atoms from NADH and H+
� This allow glycolysis to continue
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Anaerobic Respiration
� Lactic Acid Fermentation � This process helps to produce certain foods
like yogurt and cheese � Also occurs during strenuous exercise ○ What happens when you have too much lactic
acid in your blood?
Anaerobic Respiration � Ethyl Alcohol Fermentation
� A two step process occurs to create CO2 and ethanol
Anaerobic Respiration
� Not very efficient at converting pyruvic acid into energy � Only about 3.5% of the potential energy is
created through the anaerobic pathway � Why do organisms use anaerobic
respiration if it is inefficient?
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Aerobic Respiration � The process of creating energy when oxygen is present � There are two major stages
� Krebs cycle � Electron Transport Chain
� Occurs inside the mitochondria � First step after glycolysis
� Pyruvic acid reacts with coenzyme A to form acetyl coenzyme A (acetyl CoA)
� NADH is produced
Aerobic Respiration
� The Krebs Cycle � Acetyl CoA is used to produce CO2,
hydrogen atoms, and ATP � Done in 9 steps � Only 2 ATP directly produced � 3 NADH molecules produced � 1 FADH2 molecule is produced
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Aerobic Respiration
� Electron Transport Chain � The mitochondria takes all the NADH and
FADH2 and turns it into ATP
Aerobic Respiration
� How much Energy is produced? � Glycolysis and the Krebs cycle produce 2
ATP ○ 4 ATP
� Every NADH molecule makes 3 ATP ○ Total of 10 NADH = 30 ATP
� Every FADH2 molecule makes 2 ATP ○ Total of 2 FADH2 = 4 ATP
� Grand total = 38 ATP