1. Lesson Overview Lesson Overview Cellular Respiration: An Overview Lesson Overview Cellular Respiration

2. Lesson Overview Lesson Overview Cellular Respiration: An Overview Chemical Energy and Food Food provides living things with the chemical building blocks they need to grow and reproduce. Food molecules contain chemical energy that is released when its chemical bonds are broken.

3. Lesson Overview Lesson Overview Cellular Respiration: An Overview Chemical Energy and Food Cells use all sorts of molecules for food, including fats, proteins, and carbohydrates. The energy stored in each of these molecules varies because their chemical structures, and therefore their energy-storing bonds, differ. Cells break down food molecules gradually and use the energy stored in the chemical bonds to produce compounds such as ATP that power the activities of the cell.

4. Lesson Overview Lesson Overview Cellular Respiration: An Overview Overview of Cellular Respiration If oxygen is available, organisms can obtain energy from food by a process called cellular respiration. The summary of cellular respiration is presented below. In symbols: 6 O 2 + C 6 H 12 O 6  6 CO 2 + 6 H 2 O + Energy In words: Oxygen + Glucose  Carbon dioxide + Water + Energy 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.

5. Lesson Overview Lesson Overview Cellular Respiration: An Overview Stages of Cellular Respiration The three main stages of cellular respiration are: glycolysis the Krebs cycle (citric acid cycle) the electron transport chain

6. Lesson Overview Lesson Overview Cellular Respiration: An Overview Stages of Cellular Respiration Glycolysis produces only a small amount of energy. Most of glucose’s energy (90%) remains locked in the chemical bonds of pyruvic acid at the end of glycolysis.

7. Lesson Overview Lesson Overview Cellular Respiration: An Overview Stages of Cellular Respiration During the Krebs cycle, a little more energy is generated from pyruvic acid.

8. Lesson Overview Lesson Overview Cellular Respiration: An Overview Stages of Cellular Respiration The electron transport chain produces the bulk of the energy in cellular respiration by using oxygen, a powerful electron acceptor.

9. Lesson Overview Lesson Overview Cellular Respiration: An Overview Oxygen and Energy Pathways of cellular respiration that require oxygen are called aerobic. The Krebs cycle and electron transport chain are both aerobic processes. Both processes take place inside the mitochondria.

10. Lesson Overview Lesson Overview Cellular Respiration: An Overview Oxygen and Energy Gylcolysis is an anaerobic process. It does not directly require oxygen, nor does it rely on an oxygen- requiring process to run. However, it is still considered part of cellular respiration. Glycolysis takes place in the cytoplasm of a cell.

11. Lesson Overview Lesson Overview Cellular Respiration: An Overview Comparing Photosynthesis and Cellular Respiration Photosynthesis and cellular respiration are opposite processes. The energy flows in opposite directions. Photosynthesis “deposits” energy, and cellular respiration “withdraws” energy. The reactants of cellular respiration are the products of photosynthesis and vice versa.

12. Lesson Overview Lesson Overview Cellular Respiration: An Overview Comparing Photosynthesis and Cellular Respiration The release of energy by cellular respiration takes place in plants, animals, fungi, protists, and most bacteria. Energy capture by photosynthesis occurs only in plants, algae, and some bacteria.

13. Lesson Overview Lesson Overview Cellular Respiration: An Overview Glycolysis Glycolysis is the first stage of cellular respiration and takes place is the cytoplasm. During glycolysis, glucose is broken down into 2 molecules of the 3-carbon molecule pyruvic acid. Pyruvic acid is a reactant in the Krebs cycle. ATP and NADH are produced as part of the process.

14. Lesson Overview Lesson Overview Cellular Respiration: An Overview ATP Production The cell uses 2 ATP molecules into its “account” to get glycolysis going. Glycolysis then produces 4 ATP molecules. Glycolysis gives the cell a net gain of 2 ATP molecules for each molecule of glucose.

15. Lesson Overview Lesson Overview Cellular Respiration: An Overview The Advantages of Glycolysis Glycolysis produces ATP very fast, which is an advantage when the energy demands of the cell suddenly increase. Glycolysis does not require oxygen, so it can quickly supply energy to cells when oxygen is unavailable.

16. Lesson Overview Lesson Overview Cellular Respiration: An Overview The Krebs Cycle During the Krebs cycle, the second stage of cellular respiration, pyruvic acid produced in glycolysis is broken down into carbon dioxide in a series of energy-extracting reactions.

17. Lesson Overview Lesson Overview Cellular Respiration: An Overview Krebs Cycle The Krebs cycle occurs in the mitochondrial matrix and generates a pool of chemical energy (ATP, NADH, and FADH2) from the oxidation of pyruvate, the end product of glycolysis. Pyruvate is transported into the mitochondria and loses carbon dioxide to form acetyl-CoA, a 2- carbon molecule.

18. Lesson Overview Lesson Overview Cellular Respiration: An Overview Krebs Cycle When acetyl-CoA is oxidized to carbon dioxide in the Krebs cycle, chemical energy is released and captured in the form of NADH, FADH2, and ATP. Which are used in the electron transport chain to generate more ATP. So, for each glucose molecule, 6 CO2 molecules, 2 ATP molecules, 8 NADH molecules, and 2 FADH2 molecules are produced at the end of the Krebs Cycle

19. Lesson Overview Lesson Overview Cellular Respiration: An Overview Electron Transport Chain NADH and FADH 2 pass their high-energy electrons to electron carrier proteins in the electron transport chain.

20. Lesson Overview Lesson Overview Cellular Respiration: An Overview Electron Transport At the end of the electron transport chain, the electrons combine with H + ions and oxygen to form water.

21. Lesson Overview Lesson Overview Cellular Respiration: An Overview Electron Transport Energy generated by the electron transport chain is used to move H+ ions against a concentration gradient across the inner mitochondrial membrane.

22. Lesson Overview Lesson Overview Cellular Respiration: An Overview ATP Production H+ ions pass back across the mitochondrial membrane to produce ATP.

23. Lesson Overview Lesson Overview Cellular Respiration: An Overview Energy Totals In the presence of oxygen, the complete breakdown of glucose through cellular respiration results in the production of 36 ATP molecules. This represents about 36 percent of the total energy of glucose. The remaining 64 percent is released as heat.

24. Lesson Overview Lesson Overview Cellular Respiration: An Overview Energy Totals The cell can generate ATP from just about any source, even though we’ve modeled it using only glucose. Complex carbohydrates are broken down into simple sugars like glucose. Lipids and proteins can be broken down into molecules that enter the Krebs cycle or glycolysis at one of several places.

25. Lesson Overview Lesson Overview Cellular Respiration: An Overview

26. Lesson Overview Lesson Overview Cellular Respiration: An Overview Lesson Overview 9.3 Fermentation

27. Lesson Overview Lesson Overview Cellular Respiration: An Overview Fermentation Fermentation is a process by which energy can be released from food molecules in the absence of oxygen. Fermentation occurs in the cytoplasm of cells.

28. Lesson Overview Lesson Overview Cellular Respiration: An Overview Fermentation Under anaerobic conditions, fermentation follows glycolysis. During fermentation, cells convert NADH produced by glycolysis back into the electron carrier NAD +, which allows glycolysis to continue producing ATP.

29. Lesson Overview Lesson Overview Cellular Respiration: An Overview Alcoholic Fermentation Yeast and a few other microorganisms use alcoholic fermentation that produces ethyl alcohol and carbon dioxide. This process is used to produce alcoholic beverages and causes bread dough to rise.

30. Lesson Overview Lesson Overview Cellular Respiration: An Overview Alcoholic Fermentation Chemical equation: Pyruvic acid + NADH  Alcohol + CO 2 + NAD +

31. Lesson Overview Lesson Overview Cellular Respiration: An Overview Lactic Acid Fermentation Most organisms, including humans, carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid. Chemical equation: Pyruvic acid + NADH  Lactic acid + NAD +

32. Lesson Overview Lesson Overview Cellular Respiration: An Overview Energy and Exercise How does the body produce ATP during different stages of exercise? For short, quick bursts of energy, the body uses ATP already in muscles as well as ATP made by lactic acid fermentation. For exercise longer than about 90 seconds, cellular respiration is the only way to continue generating a supply of ATP.

33. Lesson Overview Lesson Overview Cellular Respiration: An Overview Quick Energy Cells normally contain small amounts of ATP produced during cellular respiration, enough for a few seconds of intense activity. Lactic acid fermentation can supply enough ATP to last about 90 seconds. However, extra oxygen is required to get rid of the lactic acid produced. 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.

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

35. Lesson Overview Lesson Overview Cellular Respiration: An Overview Long-Term Energy Hibernating animals, such as a brown bear, rely on stored fat for energy when they sleep through the winter.