Cellular Respiration

Overview of Cellular Respiration Section 4.4Cellular respiration makes ATP by breaking

down sugars.If a step requires oxygen, it is called aerobic.If a step occurs in the absence of oxygen, it

is called anaerobic.It takes place in three steps:

GlycolysisKrebs cycleElectron transport chain

Cellular respiration The equation for cellular respiration is:C6H12O6 + 6 O2 6 H2O + 6 CO2 + energy

The equation for photosynthesis is:6 H2O + 6 CO2 + light energyC6H12O6 + 6

O2

Comparing photosynthesis with respiration

GlycolysisIs anaerobicOccurs in the cytoplasmOne 6 carbon glucose molecule is broken

down into two three carbon pyruvate molecules.

Produces 2 ATP molecules

Krebs CycleIs aerobicOccurs in mitochondriaPyruvate is broken down

One 2 carbon molecule 1 CO2 moleculeHigh energy electrons

CoEnzyme A bonds to the 2 carbon molecule

Krebs CycleAcetyl CoA enters the Krebs cycle (2C)Combines with a 4 carbon

molecule to form citric acid (6C)

Loses a CO2 (5C)

Loses another CO2 (4C)Combines with acetyl CoA.Produces 2 ATP

Electron Transport ChainIs aerobicOccurs in mitochondriaNADH and FADH2 donate electrons and

transport hydrogen ions.Produces 34 ATP moleculesHydrogen ions and electrons combine with

oxygen to produce water.

Electron Transport Chain

Aerobic respirationAerobic respiration can produce up

to 38 ATP molecules from 1 molecule of glucose.

Most ATP is produced in the electron transport chain.

Anaerobic RespirationAlso called fermentationIn the absence of oxygenIf there is no oxygen to accept electrons or

hydrogen ionsNADH and FADH2 cannot be converted

to NAD+ and FAD2+

Citric acid is not broken down in the Krebs cycle

Acetyl CoA cannot enter the Krebs cycle

Anaerobic respirationPyruvate has to be broken down another

way.In yeasts:

Pyruvate ethanol and CO2

Produces 2 ATP moleculesIn animals:

Pyruvate lactic acidProduces 2 ATP molecules

Uses of fermentationCheeseAlcoholBreads