chapter nine- cellular respiration & fermentation

Copyright Pearson Prentice Hall

9-1 Chemical Pathways

Food serves as a source of raw materials for the cells in the body and as a source of energy.

Animal

Animal Cells

Plant Cells

Mitochondrion

Both plant and animal cells carry out cellular respiration in the mitochondria.

Animal Cells

Plant Cells

MitochondrionOuter membrane Intermembrane

Inner membrane

Matrix

Chemical Energy and FoodOne gram of the sugar glucose (C6H12O6), when burned in the presence of oxygen, releases 3811 calories of heat energy.A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius.

Cells don't “burn” glucose. Instead, they gradually release the energy from glucose and other food compounds.

This process begins with a pathway called glycolysis.Glycolysis releases a small amount of energy.

Overview of Cellular Respiration

If oxygen is present, glycolysis is followed by the Krebs cycle and the electron transport chain.Glycolysis, the Krebs cycle, and the electron transport chain make up a process called cellular respiration.

Cytoplasm

Pyruvicacid

Mitochondrion

Electrons carried in NADH

Electrons carried in NADH and FADH2

Glucose Glycolysis

Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.

The equation for cellular respiration is:

6O2 + C6H12O6 → 6CO2 + 6H2O + Energyoxygen glucose carbon water energy dioxide

Each of the three stages of cellular respiration captures some of the chemical energy available in food molecules and uses it to produce ATP.

Glycolysis takes place in the cytoplasm. The Krebs cycle and electron transport take place in the mitochondria.

CytoplasmMitochondrion

Glycolysis

2 ADP 4 ADP 4 ATP

2 Pyruvicacid

Glucose

In glycolysis, one molecule of glucose is broken in half, producing two molecules of pyruvic acid.

Glycolysis requires 2 ATP to start the reaction. When glycolysis is complete, 4 ATP molecules have been produced.

2 ADP 4 ADP 4 ATP2 ATP

Glucose2 Pyruvicacid

Glycolysis gives the cell a net gain of 2 ATP molecules.

4 ADP 4 ATP

Glucose

2 ADP2 ATP

2 Pyruvicacid

NADH ProductionOne reaction of glycolysis removes 4 high-energy electrons, passing them to an electron carrier called NAD+.

4 ADP 4 ATP2 ADP2 ATP

Each NAD+ accepts a pair of high-energy electrons and becomes an NADH molecule.

2NAD+ 2

The NADH molecule holds high energy electrons until they can be transferred to other molecules.

To the electrontransport chain

2NAD+ 2 Pyruvicacid

The Advantages of GlycolysisThe process of glycolysis is so fast that cells can produce thousands of ATP molecules in a few milliseconds.Glycolysis does not require oxygen.

Glycolysismakes

Krebs cycle and fermentationelectron transport

With oxygen

Without oxygen

Fermentation

When oxygen is not present, glycolysis is followed by a different pathway. The combined process of this pathway and glycolysis is called fermentation.Fermentation releases energy from food molecules by producing ATP in the absence of oxygen.

During fermentation, cells convert NADH to NAD+ by passing high-energy electrons back to pyruvic acid.This action converts NADH back into NAD+, and allows glycolysis to continue producing a steady supply of ATP.

Fermentation does not require oxygen—it is an anaerobic process.

The two main types of fermentation are lactic acid fermentation and alcoholic fermentation.

Yeasts use alcoholic fermentation to get energy from pyruvic acid.Alcoholic fermentation forms ethanol and carbon dioxide as wastes.

In lactic acid fermentation, the pyruvic acid and NADH from glycolysis are converted to lactic acid.It regenerates NAD+ so that glycolysis can continue.

The first part of the equation is glycolysis.

The second part shows the conversion of pyruvic acid to lactic acid.

Energy needs are great when you exercise.

If oxygen is limited, muscle cells will produce energy by lactic acid fermentation.

Lactic acid buildup in muscles will cause soreness and cramps.

Proper breathing will promote cellular respiration.

9-2 The Krebs Cycle and Electron Transport

Oxygen is required for the final steps of cellular respiration.Because the pathways of cellular respiration require oxygen, they are aerobic.

In the presence of oxygen, pyruvic acid produced in glycolysis enters the Krebs cycle.

The Krebs Cycle

During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.

The Krebs Cycle

The Krebs cycle begins when pyruvic acid produced by glycolysis enters the mitochondrion.

The Krebs Cycle

One carbon is removed, forming CO2, and electrons are removed, changing NAD+ to NADH.

The Krebs Cycle

Coenzyme A joins the 2-carbon molecule, forming acetyl-CoA.

The Krebs Cycle

Citric acid

Acetyl-CoA then adds the 2-carbon acetyl group to a 4-carbon compound, forming citric acid.

Citric acid is broken down into a 5-carbon compound, then into a 4-carbon compound.

Two more molecules of CO2 are released and electrons join NAD+ and FAD, forming NADH and FADH2

The Krebs Cycle

In addition, one molecule of ATP is generated.

The Krebs Cycle

The energy tally from 1 molecule of pyruvic acid is • 4 NADH- electron carrier• 1 FADH2- electron carrier• 1 ATP- energy carrier

The Krebs Cycle

What does the cell do with all those high-energy electrons in carriers like NADH?In the electron transport chain, the high-energy electrons from NADH and FADH2 are used to generate huge amounts of ATP.

Electron Transport

The electron transport chain uses the high-energy electrons from the Krebs cycle to convert ADP into ATP.

High-energy electrons from NADH and FADH2 are passed along the electron transport chain from one carrier protein to the next.

Electron Transport

At the end of the chain, an enzyme combines these electrons with hydrogen ions and oxygen to form water.

As the final electron acceptor of the electron transport chain, oxygen gets rid of the low-energy electrons and hydrogen ions.

When 2 high-energy electrons move down the electron transport chain, their energy is used to move hydrogen ions (H+) across the membrane.

During electron transport, H+ ions build up in the intermembrane space, so it is positively charged.

The other side of the membrane, from which those H+ ions are taken, is now negatively charged.

ATP synthase

The inner membranes of the mitochondria contain protein spheres called ATP synthases.

As H+ ions escape through channels into these proteins, the ATP synthase spins.

ATP synthase

Channel

As it rotates, the enzyme grabs a low-energy ADP, attaching a phosphate, forming high-energy ATP.

ATP synthase

Channel

On average, each pair of high-energy electrons that moves down the electron transport chain provides enough energy to produce three molecules of ATP from ADP.

The Totals

Glycolysis produces just 2 ATP molecules per molecule of glucose.The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.

The Totals

Comparing Photosynthesis and Cellular Respiration

Photosynthesis and cellular respiration are the same chemical reaction except in opposite directions.

Same reaction flipped over!

Photosynthesis + 6CO2 + 6H2O C6H12O6 + 6O2

Cellular RespirationC6H12O6 + 6O2 6CO2 + 6H2O + Energy

Energy in

Photosynthesis in the chloroplast Only plants and algae have

chloroplasts

Cellular respiration in the mitochondria

Almost all eukaryotes have mitochondria

On a global level, photosynthesis and cellular respiration are also opposites.

•Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back.

•Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food.

The raw materials required for cellular respiration are

a. carbon dioxide and oxygen.

b. glucose and water.

c. glucose and oxygen.

d. carbon dioxide and water.

Glycolysis occurs in the

a. mitochondria.

b. cytoplasm.

c. nucleus.

d. chloroplasts.

The net gain of ATP molecules after glycolysis is

a. 3 ATP molecules.

b. 2 ATP molecules.

c. 3 pyruvic acid molecules.

d. 4 pyruvic acid molecules

Fermentation releases energy from food molecules in the absence of

a. oxygen.

b. glucose.

c. NADH.

d. alcohol.

The first step in fermentation is always

a. lactic acid production.

b. the Krebs cycle.

c. glycolysis.

d. alcohol production.

The Krebs cycle breaks pyruvic acid down into

a. oxygen.

b. NADH.

c. carbon dioxide.

d. alcohol.

What role does the Krebs cycle play in the cell?

a. It breaks down glucose and releases its stored energy.

b. It releases energy from molecules formed during glycolysis.

c. It combines carbon dioxide and water into high-energy molecules.

d. It breaks down ATP and NADH, releasing stored energy.

In eukaryotes, the electron transport chain is located in the

a. cell membrane.

b. inner mitochondrial membrane.

c. cytoplasm.

d. outer mitochondrial membrane.

To generate energy over long periods, the body must use

a. stored ATP.

b. lactic acid fermentation.

c. cellular respiration.

d. glycolysis.

Which statement correctly describes photosynthesis and cellular respiration?

a. Photosynthesis releases energy, while cellular respiration stores energy.

b. Photosynthesis and cellular respiration use the same raw materials.

c. Cellular respiration releases energy, while photosynthesis stores energy.

d. Cellular respiration and photosynthesis produce the same products.

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