Chapter 9: Cellular Respiration and Fermentation

Section 9.1: Cellular Respiration: An Overview

I. Chemical Energy and Food a. Food molecules contain chemical energy that is released when its chemical bonds are broken. b. Cells break down food molecules gradually and use the energy stored in the chemical bonds to produce ATP that power the activities of the cell.

c. Energy stored in food is expressed in units of calories d. Calorie: amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius i. 1000 calories = 1 kilocalorie, or Calorie.

II. Overview of Cellular Respiration a. Cellular Respiration: process in which organisms can obtain energy from food if oxygen is present In symbols: 6 O2 + C6H12O6  6 CO2 + 6 H2O + Energy In words: Oxygen + Glucose  Carbon dioxide + Water + Energy b. The cell has to release the chemical energy in food molecules (like glucose) gradually, otherwise most of the energy would be lost in the form of heat and light.

III. Stages of Cellular Respiration a. The three main stages: i. Glycolysis ii. The Krebs cycle iii. The electron transport chain

Glycolysis produces only a small amount of energy i. Most of glucose’s energy (90%) remains locked in the chemical bonds of pyruvic acid at the end of glycolysis

c. The Krebs cycle little more energy is generated from pyruvic acid

d. The electron transport chain produces the bulk of the energy by using oxygen, a powerful electron acceptor

IV. Oxygen and Energy a. Aerobic Respiration: pathways of cellular respiration that require oxygen i. The Krebs cycle and electron transport chain ii. Both processes take place inside the mitochondria

b. Anaerobic Respiration: pathway that des not directly require oxygen to run i. Gylcolysis ii. Glycolysis takes place in the cytoplasm of a cell

V. Comparing Photosynthesis and Cellular Respiration a. Photosynthesis and cellular respiration are opposite processes. b. The energy flows in opposite directions. i. photosynthesis “deposits” energy ii. cellular respiration “withdraws” energy. c. The reactants of cellular respiration are the products of photosynthesis

Section 9.2: The Process of Cellular Respiration

I. Glycolysis a. Glycolysis is the first stage of cellular respiration. b. glucose is broken down into 2 molecules of the 3-carbon molecule pyruvic acid. c. Pyruvic acid is a reactant in the Krebs cycle. d. ATP and NADH are produced as part of the process.

II. The Advantages of Glycolysis a. Produces ATP very fast, which is an advantage when the energy demands of the cell suddenly increase. b. Does not require oxygen, so it can quickly supply energy to cells when oxygen is unavailable.

III. The Krebs Cycle a. pyruvic acid produced in glycolysis is broken down into carbon dioxide in a series of energy-extracting reactions b. also known as the citric acid cycle

IV. Electron Transport a. NADH and FADH2 pass their high-energy electrons to electron carrier proteins

b. At the end of the electron transport chain, the electrons combine with H+ ions and oxygen to form water

V. ATP Production a. H+ ions pass back across the mitochondrial membrane through the ATP synthase, causing the ATP synthase molecule to spin. b. With each rotation, the ATP synthase attaches a phosphate to ADP to produce ATP.

VI. Energy Totals a. In the presence of oxygen, the complete breakdown of glucose through cellular respiration results in the production of 36 ATP molecules. b. This represents about 36 percent of the total energy of glucose. c. The remaining 64 percent is released as heat.

Section 9.3: Fermentation

I. Fermentation a. Fermentation: process by which energy can be released from food molecules in the absence of oxygen b. occurs in the cytoplasm of cells.

c. Under anaerobic conditions, fermentation follows glycolysis. d. cells convert NADH produced by glycolysis back into the electron carrier NAD+, which allows glycolysis to continue producing ATP.

II. Alcoholic Fermentation Yeast and a few other microorganisms use alcoholic fermentation that produces ethyl alcohol and carbon dioxide. Chemical equation: Pyruvic acid + NADH  Alcohol + CO2 + NAD+

III. Lactic Acid Fermentation a. Most organisms carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid. b. Chemical equation: Pyruvic acid + NADH  Lactic acid + NAD+

IV. Quick Energy a. Cells normally contain small amounts of ATP produced during cellular respiration, enough for a few seconds of intense activity. b. Lactic acid fermentation can supply enough ATP to last about 90 seconds. c. However, extra oxygen is required to get rid of the lactic acid produced d. Following intense exercise, a person will huff and puff for several minutes in order to pay back the built-up “oxygen debt” and clear the lactic acid from the body.

V. Long-Term Energy a. For intense exercise lasting longer than 90 seconds, cellular respiration is required to continue production of ATP b. Cellular respiration releases energy more slowly than fermentation does c. The body stores energy in the form of the carbohydrate glycogen d. Glycogen stores are enough to last for 15 to 20 minutes of activity e. After that, the body begins to break down other stored molecules, including fats, for energy