Cellular respiration
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Cellular Respiration. Chemical Energy and Food. Food is the energy source for cells. The energy in food is measured in calories. A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius. There are 3811 calories in one gram of sugar glucose.

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Cellular respiration
Cellular Respiration

Chemical energy and food
Chemical Energy and Food

  • Food is the energy source for cells. The energy in food is measured in calories.

  • A calorieis the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius. There are 3811 calories in one gram of sugar glucose.

  • The cell doesn’t burn glucose directly but converts into an energy source, ATP, through a process that begins with the pathway called glycolysis.


  • Glycolysis is the process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid, a three carbon compound.

  • Glycolysis takes place in the cytoplasm of a cell.

  • In the process of breaking glucose in half two molecules of ATP are needed but four molecules of ATP are produced creating a net gain of two molecules of ATP

  • 4 high energy electrons are also removed and added to NAD+ (nicotinamide adenine dinucleotide) creating NADH, which helps pass energy from glucose to other pathways in the cell.



2 Pyruvic acid

To the electron transport chain

Chemical pathways after glycolysis
Chemical Pathways After Glycolysis


Krebs cycle



Alcohol or lactic acid

Fermentation (without oxygen)


  • When oxygen is not present, fermentation follows glycolysis

  • ● Fermentation releases energy from food molecules by producing ATP in the absence of oxygen, this is an anaerobic process.

  • ● There are two main types of fermentation:

  • Alcoholic fermentation

  • Lactic acid fermentation

  • ● Alcoholic fermentation example is yeast which causes carbon dioxide to form and make bread rise.

  • ● pyruvic acid + NADH  alcohol + CO2 + NAD+


  • ● Lactic acid fermentation:

  • Pyruvic acid + NADH lactic acid + NAD+

  • ● Lactic acid is produced in your muscles during rapid exercise when the body cannot supply enough oxygen to the tissues.

  • ● “FEEL THE BURN” is actually the result of a build up of lactic acid in the muscles and can become painful and lead to cramps.

Lactic acid fermentation
Lactic Acid Fermentation

Lactic acid


Pyruvic acid

Overview of cellular respiration
Overview of Cellular Respiration

  • If oxygen is present, The Krebs Cycle and electron transport chain follow glycolysis

  • Glycolysis, the Krebs Cycle, and the electron transport chain make up the process called cellular respiration.

  • Cellular respirationis the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen (an aerobic process).

    Cellular Respiration Chemical Equation

Cellular respiration an overview
Cellular Respiration: An Overview


Electrons carried in NADH

Electrons carried in NADH and FADH2

Pyruvic acid


Electron Transport Chain

Krebs Cycle




The krebs cycle citric acid cycle
The Krebs Cycle (Citric Acid Cycle)

  • The Krebs cycle is the 2nd stageof cellular respiration. (glycolysis is the 1st stage)

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

  • The Krebs cycle is also known as the citric acid cycle, because citric acid is one of its 1st products.

Stages of the krebs cycle
Stages Of The Krebs Cycle

  • The Krebs cycle starts when pyruvic acid formed by glycolysis enters the mitochondrion.

  • The pyruvic acid is broken down into carbon dioxide and a 2-carbon acetyl group.

  • The 2 carbons of the acetyl group join a 4-carbon compound to produce citric acid. The Krebs cycle continues in a series of reactions. In these reactions, two energy carriers accept high-energy electrons. NAD+ is changed to NADH, and FAD is changed to FADH2. These molecules carry high energy electrons to the electron transport chain. The carbon dioxide is released as a waste product.

The krebs cycle
The Krebs Cycle

Citric Acid Production


The electron transport chain etc
The Electron Transport Chain (ETC)

  • The ETC is the 3rd and final stage of cellular respiration.

  • The ETC uses the high energy electrons to change ADP into ATP.

  • In the ETC, high energy electrons move from one carrier protein to the next.

  • At the end of the chain, oxygen pulls electrons from the final carrier molecule. These electrons join with hydrogen ions, forming water.

  • Each transfer along the chain releases a small amount of energy. ATP synthase uses the energy to produce ATP.

Electron transport chain
Electron Transport Chain

Electron Transport

Hydrogen Ion Movement





ATP synthase




ATP Production

Cellular respiration overview
Cellular Respiration Overview













Atp totals for cellular respiration
ATP Totals For Cellular Respiration

  • ● The totals for the cellular respiration cycle are as follows:

  • -Glycolysis: +4 ATP – 2 ATP = Net gain 2 ATP

  • -Krebs Cycle and ETC: +32 ATP

  • -Net gain for entire cycle is 34 ATP

  • Note: remember there are 2 ATP used in glycolysis, therefore only 34 ATP are realized for the cell’s further needs.

  • -The total number of ATP molecules formed during cellular respiration is 36

The partnership between photosynthesis and cellular respiration
The Partnership Between Photosynthesis And Cellular Respiration

  • The energy flows in photosynthesis and cellular respiration occur in opposite directions.

  • On a global level, photosynthesis removes carbon dioxide from the atmosphere and puts back oxygen.

  • Cellular respiration removes oxygen from the atmosphere and puts back carbon dioxide.