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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