Chapter 7Deriving Energy From Food

– Both plants and animals perform cellular respiration.• The waste products of cellular

respiration, CO2 and H2O, are used in photosynthesis.

Storing and Releasing EnergyStoring and Releasing EnergyWhere Does The Energy Come From?Where Does The Energy Come From?

Figure 7.1

Redox Reactions – pg. 125Redox Reactions – pg. 125• Oxidation-reduction (redox) reactions:

– Electrons pass from one molecule to another

• The molecule that loses an electron is oxidized

• The molecule that gains an electron is reduced

– Both take place at same time

– One molecule accepts the electron given up by the other

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Cellular Respiration – pg. 127Cellular Respiration – pg. 127

– Cellular respiration is the process by which cells acquire energy by breaking down nutrient molecules • chemical energy is harvested from food and

converted to ATP.• Consumes oxygen and produces carbon dioxide• Is an aerobic process (pg. 127)

Cellular Respiration OverviewCellular Respiration OverviewStages of Cellular Respiration:

– Glycolysis (“sugar splitting”)2. Citric Acid Cycle (Krebs Cycle)3. Electron Transport Chain (ETC)

Stage 1: GlycolysisStage 1: Glycolysis

– Glycolysis means “splitting of sugar”– Takes place in the cytoplasm

– A molecule of glucose (C6) is split into two molecules of pyruvate (pyruvic acid C3).

• 2 ATP produced per glucose

six-carbon glucose

Three-carbon pyruvic acid

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Stage 2: Krebs CycleStage 2: Krebs Cycle

• Occurs in the mitochondria – aerobic process• Turns twice per glucose molecule (one for

each pyruvate)

• Forms coenzymes NADH and FADH2 which serve as electron carriers = 2 ATP (one per acetic acid)

• Also known as the Citric Acid Cycle

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Stage 3: Electric Transport Chain (ETC)Stage 3: Electric Transport Chain (ETC)

• Electron transport releases the energy your cells need to make most of their ATP

• Occurs in the mitochondria• Creates a H+ gradient = As the electrons are

passed between carrier proteins through the chain, energy is released in the form of ATP

• Oxygen serves as the final electron acceptor• Movement of electrons = 32 – 34 ATP

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Cellular Respiration OverviewCellular Respiration OverviewStages of Cellular Respiration:

1. Glycolysis• Occurs in the cytoplasm• Glucose to 2 pyruvate = 2 ATP

2. Krebs Cycle (Citric Acid Cycle)• Occurs in the mitochondria

• Coenzymes NADH and FADH2 = 2 ATP

3. Electron Transport Chain (ETC)• Occurs in the mitochondria• Movement of electrons = 32 – 34 ATP

ATP from Cellular RespirationATP from Cellular Respiration

Overall Energy YieldOverall Energy Yield

• Net yield per glucose:

– From glycolysis – 2 ATP

– From citric acid cycle – 2 ATP

– From electron transport chain – 32 or 34 ATP

• Energy content:

– Energy yield (36 ATP) 263 kcal

– Efficiency is 39%

– The rest of the energy from glucose is lost as heat

Fermentation: Anaerobic RespirationFermentation: Anaerobic Respiration

• If O2 is not available to the cell, fermentation, an anaerobic process, occurs in the cytoplasm. – During fermentation, glucose is incompletely

metabolized to lactate, or to CO2 and alcohol (depending on the organism). – pg. 130

– Yields 2 ATP

FERMENTATIONFERMENTATION• Lactic Acid Fermentation

– Happens in muscle cells • Lactic acid

• Alcohol Fermentation– Happens in some bacteria and YEAST

• brewing, wine making, and baking• ethyl alcohol & CO2

http://videos.howstuffworks.com/discovery/34874-howstuffworks-show-episode-5-fermentation-video.htm

Metabolic PoolMetabolic Pool

• Foods are sources of energy rich molecules such as carbohydrates, fats, and proteins

• Degradative reactions (catabolism) break down molecules

– Tend to be exergonic (release energy)

• Synthetic reactions (anabolism) build molecules

– Tend to be endergonic (consume energy)

Comparing Aerobic & Anaerobic Comparing Aerobic & Anaerobic Cellular Respiration PathwaysCellular Respiration Pathways

236Net ATP production:

Ethanol + CO2 or lactic acid

6 CO2 + 6 H2O1 glucose makes:

Mostly yeast and bacteria

Most organismsOccurs in:

Anaerobic Aerobic

**NOTICE – Aerobic respiration is more efficient!!

Comparing Photosynthesis & Comparing Photosynthesis & RespirationRespiration

C6H12O6 + 6O2

6CO2 + 6H2O

6CO2 + 6H2O C6H12O6 + 6O2

Equation

CO2 and H2OC6H12O6 and O2Products

C6H12O6 and O2CO2 and H2OReactants

MitochondriaChloroplastsLocation

Energy ReleaseEnergy StorageFunction

Cellular Respiration

Photosynthesis