Chapter Intro-page 220 What You’ll Learn You will recognize why organisms need a constant supply of energy and where that energy comes from. You will identify how cells store and release energy as ATP. You will describe the pathways by which cells obtain energy.

Chapter Intro-page 220 What You’ll Learn You will compare ATP production in mitochondria and in chloroplasts.

9.1 Section Objectives – page 221 Explain why organisms need a supply of energy. Section Objectives: Describe how energy is stored and released by ATP.

Section 9.1 Summary – pages All living organisms must be able to obtain energy from the environment in which they live. Plants and other green organisms are able to trap the light energy in sunlight and store it in the bonds of certain molecules for later use. Cell Energy

Section 9.1 Summary – pages Other organisms cannot use sunlight directly. They eat green plants. In that way, they obtain the energy stored in plants. Cell Energy

Section 9.1 Summary – pages Active transport, cell division, movement of flagella or cilia, and the production, transport, and storage of proteins are some examples of cell processes that require energy. Work and the need for energy There is a molecule in your cells that is a quick source of energy for any organelle in the cell that needs it.

Section 9.1 Summary – pages The name of this energy molecule is adenosine triphosphate or ATP for short. ATP is composed of an adenosine molecule with three phosphate groups attached. Work and the need for energy

Section 9.1 Summary – pages The charged phosphate groups act like the positive poles of two magnets. Bonding three phosphate groups to form adenosine triphosphate requires considerable energy. Forming and Breaking Down ATP

Section 9.1 Summary – pages When only one phosphate group bonds, a small amount of energy is required and the chemical bond does not store much energy. This molecule is called adenosine monophosphate (AMP). Forming and Breaking Down ATP When a second phosphate group is added, more energy is required to force the two groups together. This molecule is called adenosine diphosphate, or ADP.

Section 9.1 Summary – pages An even greater amount of energy is required to force a third charged phosphate group close enough to the other two to form a bond. When this bond is broken, energy is released. Forming and Breaking Down ATP

Section 9.1 Summary – pages The energy of ATP becomes available to a cell when the molecule is broken down. Adenosine PPP P P PP Adenosine triphosphate (ATP) Adenosine diphosphate (ADP) Forming and Breaking Down ATP

Section 9.1 Summary – pages When ATP is broken down and the energy is released, the energy must be captured and used efficiently by cells. Many proteins have a specific site where ATP can bind. How cells tap into the energy stored in ATP

Section 9.1 Summary – pages Then, when the phosphate bond is broken and the energy released, the cell can use the energy for activities such as making a protein or transporting molecules through the plasma membrane. ATP ADP Protein P Energy How cells tap into the energy stored in ATP

Section 9.1 Summary – pages When ATP has been broken down to ADP, the ADP is released from the binding site in the protein and the binding site may then be filled by another ATP molecule. How cells tap into the energy stored in ATP

9.2 Section Objectives – page 225 Relate the structure of chloroplasts to the events in photosynthesis. Section Objectives: Describe light-dependent reactions. Explain the reactions and products of the light-independent Calvin cycle.

Section 9.2 Summary – pages Trapping Energy from Sunlight The process that uses the sun’s energy to make simple sugars is called photosynthesis.

1.The light-dependent reactions convert light energy into chemical energy. Section 9.2 Summary – pages Photosynthesis happens in two phases. 2. The molecules of ATP produced in the light- dependent reactions are then used to fuel the light-independent reactions that produce simple sugars. The general equation for photosynthesis is written as 6CO 2 + 6H 2 O→C 6 H 12 O 6 + 6O 2 Trapping Energy from Sunlight

Section 9.2 Summary – pages Click image to view movie. Trapping Energy from Sunlight

Section 9.2 Summary – pages The chloroplast and pigments To trap the energy in the sun’s light, the thylakoid membranes contain pigments, molecules that absorb specific wavelengths of sunlight. Although a photosystem contains several kinds of pigments, the most common is chlorophyll. Chlorophyll absorbs most wavelengths of light except green.

Section 9.2 Summary – pages Light-Dependent Reactions As sunlight strikes the chlorophyll molecules in a photosystem of the thylakoid membrane, the energy in the light is transferred to electrons. These highly energized, or excited, electrons are passed from chlorophyll to an electron transport chain, a series of proteins embedded in the thylakoid membrane.

Section 9.2 Summary – pages Light-Dependent Reactions Sun Chlorophyll passes energy down through the electron transport chain. for the use in light-independent reactions bonds P to ADP forming ATP oxygen released splits H 2 O H+H+ NADP + NADPH Light energy transfers to chlorophyll. Energized electrons provide energy that At each step along the transport chain, the electrons lose energy.

Section 9.2 Summary – pages This “lost” energy can be used to form ATP from ADP, or to pump hydrogen ions into the center of the thylakoid disc. Electrons are re-energized in a second photosystem and passed down a second electron transport chain. Light-Dependent Reactions

Section 9.2 Summary – pages The electrons are transferred to the stroma of the chloroplast. To do this, an electron carrier molecule called NADP is used. NADP can combine with two excited electrons and a hydrogen ion (H + ) to become NADPH. NADPH will play an important role in the light-independent reactions. Light-Dependent Reactions

Section 9.2 Summary – pages Restoring electrons To replace the lost electrons, molecules of water are split in the first photosystem. This reaction is called photolysis. Sun Chlorophyll 2e - H2OH2O O 2 + 2H + 1 _ 2 H 2 O     2 _ 1 O 2 + 2e -

Section 9.2 Summary – pages The oxygen produced by photolysis is released into the air and supplies the oxygen we breathe. The electrons are returned to chlorophyll. The hydrogen ions are pumped into the thylakoid, where they accumulate in high concentration. Restoring electrons

Section 9.2 Summary – pages (CO2) The Calvin Cycle (CO 2 ) (Unstable intermediate) ATP ADP + (Sugars and other carbohydrates) NADPH NADP + (PGAL) ATP (PGAL) (RuPB)

Section 9.2 Summary – pages Carbon fixation The carbon atom from CO 2 bonds with a five-carbon sugar called ribulose biphosphate (RuBP) to form an unstable six- carbon sugar. (CO 2 ) (RuBP) The stroma in chloroplasts hosts the Calvin cycle. The Calvin Cycle

Section 9.2 Summary – pages Formation of 3- carbon molecules The six-carbon sugar formed in Step A immediately splits to form two three-carbon molecules. (Unstable intermediate) The Calvin Cycle

Section 9.2 Summary – pages The Calvin Cycle Use of ATP and NADPH A series of reactions involving ATP and NADPH from the light- dependent reactions converts the three-carbon molecules into phosphoglyceraldehyde (PGAL), three-carbon sugars with higher energy bonds. ATP NADPH NADP+ (PGAL) ADP +

Section 9.2 Summary – pages Sugar production One out of every six molecules of PGAL is transferred to the cytoplasm and used in the synthesis of sugars and other carbohydrates. After three rounds of the cycle, six molecules of PGAL are produced. (PGAL) (Sugars and other carbohydrates) The Calvin Cycle

Section 9.2 Summary – pages RuBP is replenished Five molecules of PGAL, each with three carbon atoms, produce three molecules of the five-carbon RuBP. This replenishes the RuBP that was used up, and the cycle can continue. P ADP+ ATP (PGAL) The Calvin Cycle

9.3 Section Objectives – page 231 Compare and contrast cellular respiration and fermentation. Section Objectives: Explain how cells obtain energy from cellular respiration.

Section 9.3 Summary – pages Cellular Respiration The process by which mitochondria break down food molecules to produce ATP is called cellular respiration. There are three stages of cellular respiration: glycolysis, the citric acid cycle, and the electron transport chain.

Section 9.3 Summary – pages Cellular Respiration The first stage, glycolysis, is anaerobic—no oxygen is required. The last two stages are aerobic and require oxygen to be completed.

Section 9.3 Summary – pages Glycolysis Glycolysis is a series of chemical reactions in the cytoplasm of a cell that break down glucose, a six-carbon compound, into two molecules of pyruvic acid, a three-carbon compound. Glucose 2ATP 2ADP 2PGAL 4ADP + 4P 2NAD+ 2NADH + 2H + 4ATP 2 Pyruvic acid

Section 9.3 Summary – pages Glycolysis is not very effective, producing only two ATP molecules for each glucose molecule broken down. Glucose 2ATP 2ADP 2PGAL 4ADP + 4P 2NAD+ 2NADH + 2H + 4ATP 2 Pyruvic acid Glycolysis

Section 9.3 Summary – pages Before citric acid cycle and electron transport chain can begin, pyruvic acid undergoes a series of reactions in which it gives off a molecule of CO 2 and combines with a molecule called coenzyme A to form acetyl-CoA. Pyruvic acid Outside the mitochondrion Mitochondrial membrane Inside the mitochondrion Pyruvic acid Intermediate by-product NAD + NADH + H + CO 2 Coenzyme A - CoA Acetyl-CoA Glycolysis

Section 9.3 Summary – pages The citric acid cycle The citric acid cycle, also called the Krebs cycle, is a series of chemical reactions similar to the Calvin cycle in that the molecule used in the first reaction is also one of the end products. For every turn of the cycle, one molecule of ATP and two molecules of carbon dioxide are produced.

Section 9.3 Summary – pages The Citric Acid Cycle (Acetyl-CoA) Citric acid NAD + NADH + H + O==O (CO 2 ) NAD + O==O (CO 2 ) ADP + ATP FAD FADH 2 Citric Acid Cycle NAD + NADH + H + Oxaloacetic acid The mitochondria host the citric acid cycle. NADH + H +

Section 9.3 Summary – pages The citric acid cycle Citric acid The two-carbon compound acetyl- CoA reacts with a four-carbon compound called oxaloacetic acid to form citric acid, a six-carbon molecule. Acetyl-CoA Citric acid Oxaloacetic acid

Section 9.3 Summary – pages Formation of CO 2 A molecule of CO 2 is formed, reducing the eventual product to a five-carbon compound. In the process, a molecule of NADH and H + is produced. NAD + NADH + H + O==O (CO 2 ) The citric acid cycle

Section 9.3 Summary – pages Formation of the second CO 2 Another molecule of CO 2 is released, forming a four- carbon compound. One molecule of ATP and a molecule of NADH are also produced. NAD + NADH + H + O= =O (CO 2 ) ADP + ATP The citric acid cycle

FADH 2 NADH + H + Section 9.3 Summary – pages Recycling of oxaloacetic acid The four-carbon molecule goes through a series of reactions in which FADH 2, NADH, and H + are formed. The carbon chain is rearranged, and oxaloacetic acid is again made available for the cycle. NAD + FAD The citric acid cycle

Section 9.3 Summary – pages The electron transport chain In the electron transport chain, the carrier molecules NADH and FADH 2 gives up electrons that pass through a series of reactions. Oxygen is the final electron acceptor. Enzyme Electron carrier proteins e - NADH FADH 2 NAD + FAD Electron pathway 4H + + O electrons H2OH2O H2OH2O ADP +ATP Inner membrane Center of mitochondrion Space between inner and outer membranes

Section 9.3 Summary – pages Overall, the electron transport chain adds 32 ATP molecules to the four already produced. The electron transport chain

Section 9.3 Summary – pages Fermentation During heavy exercise, when your cells are without oxygen for a short period of time, an anaerobic process called fermentation follows glycolysis and provides a means to continue producing ATP until oxygen is available again.

Section 9.3 Summary – pages Lactic acid fermentation Lactic acid fermentation is one of the processes that supplies energy when oxygen is scarce. In this process, the reactions that produced pyruvic acid are reversed. Two molecules of pyruvic acid use NADH to form two molecules of lactic acid.

Section 9.3 Summary – pages Lactic acid fermentation This releases NAD + to be used in glycolysis, allowing two ATP molecules to be formed for each glucose molecule. The lactic acid is transferred from muscle cells, to the liver that converts it back to pyruvic acid.

Section 9.3 Summary – pages Alcoholic fermentation Another type of fermentation, alcoholic fermentation, is used by yeast cells and some bacteria to produce CO 2 and ethyl alcohol.

Section 9.3 Summary – pages Comparing Photosynthesis and Cellular Respiration Photosynthesis Cellular Respiration Food synthesized Food broken down Energy from sun stored in glucose Energy of glucose released Carbon dioxide taken in Carbon dioxide given off Oxygen given off Oxygen taken in Produces sugars from PGALProduces CO2 and H 2 O Requires light Does not require light Occurs only in presence of chlorophyll Occurs in all living cells Table 9.1 Comparison of Photosynthesis and Cellular Respiration

Chapter Summary – 9.1 ATP is the molecule that stores energy for easy use within the cell. The Need for Energy ATP is formed when a phosphate group is added to ADP. When ATP is broken down, ADP and phosphate are formed and energy is released. Green organisms trap the energy in sunlight and store it in the bonds of certain molecules for later use.

Chapter Summary – 9.1 Organisms that cannot use sunlight directly obtain energy by consuming plants or other organisms that have consumed plants. The Need for Energy

Chapter Summary – 9.2 Photosynthesis is the process by which cells use light energy to make simple sugars. Chlorophyll in the chloroplasts of plant cells traps light energy needed for photosynthesis. The light reactions of photosynthesis produce ATP and result in the splitting of water molecules. Photosynthesis: Trapping the Sun’s Energy

Chapter Summary – 9.2 Photosynthesis: Trapping the Sun’s Energy The reactions of the Calvin Cycle make carbohydrates using CO 2 along with ATP and NADPH from the light reactions.

Chapter Summary – 9.3 Getting Energy to Make ATP In cellular respiration, cells break down carbohydrates to release energy. The first stage of cellular respiration, glycolysis, takes place in the cytoplasm and does not require oxygen. The citric acid cycle takes place in mitochondria and requires oxygen.