Chapter 9

Chemical Energy and Food Living things get the energy they need from food. The process of releasing the energy stored in food is cellular respiration.

Overview of Cellular Respiration In the presence of oxygen, aerobic respiration takes place. This produces 36 ATP per molecule of glucose. In the absence of oxygen, anaerobic respiration (fermentation) takes place. This produces 2 ATP per molecule of glucose.

Glucose Glycolysis Krebs cycle Electron transport Fermentation (without oxygen) Alcohol or lactic acid Chemical Pathways Section 9-1 Aerobic Anaerobic 2 232

Glycolysis Both aerobic and anaerobic respiration begin with a process known as glycolysis. This means “glucose -splitting” This takes place in the cytoplasm.

Glucose To the electron transport chain Glycolysis Section Pyruvic acid

Glycolysis If oxygen is available, the pyruvic acid molecules will be broken down further to release more energy. This is called aerobic respiration. If oxygen is unavailable, the pyruvic acid molecules will be converted to a waste product with no further release of energy. This is called anaerobic respiration, or fermentation.

Anaerobic Respiration (Fermentation) Takes place in the cytoplasm without oxygen. Two types: Alcoholic fermentation – in yeasts Pyruvic acid is converted to alcohol and carbon dioxide. Lactic acid fermentation – in bacteria and muscle cells Pyruvic acid is converted to lactic acid.

Glucose Pyruvic acid Lactic acid Section 9-1 Lactic Acid Fermentation

Alcoholic Fermentation

Aerobic Respiration In the presence of oxygen, pyruvic acid is further broken down to release additional energy. This takes place in the mitochondria. There are two steps: 1. The Krebs Cycle 2. The electron transport chain

Glucose Glycolysis Cytoplasm Pyruvic acid Electrons carried in NADH Krebs Cycle Electrons carried in NADH and FADH 2 Electron Transport Chain Mitochondrion Mitochondrial Reactions

The Krebs Cycle Also known as the citric acid cycle. 1. Pyruvic acid (from glycolysis) is broken down into carbon dioxide. 2. High energy electrons are captured by NAD and FAD and brought to the electron transport chain. Net gain of 2 ATP from this cycle. This occurs in the matrix of the mitochondrion.

Citric Acid Production The Krebs Cycle Section 9-2 Mitochondrion

Electron Transport Chain NADH and FADH2 drop off high energy electrons. These pass through a series of reactions located on the inner membrane that produce ATP. At the end, oxygen combines with hydrogen to make water. Net gain of ATP = 32

Electron Transport Chain Section 9-2 Electron Transport Hydrogen Ion Movement ATP Production ATP synthase Channel Inner Membrane Matrix Intermembrane Space Mitochondrion

ATP totals Glycolysis – 2 Krebs Cycle – 2 Electron Transport Chain – 32 Net: from one glucose molecule = 36 ATP

Aerobic Respiration Net Reaction: 6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O + 36 ATP Oxygen + glucose  carbon dioxide + water + energy

Photosynthesis & Cellular Respiration PhotosynthesisCellular Respiration FunctionEnergy captureEnergy release LocationChloroplastsMitochondria ReactantsCO 2 & H 2 OC 6 H 12 O 6 & O 2 ProductsC 6 H 12 O 6 & O 2 CO 2 and H 2 O Equation6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O