Cellular Respiration
Objectives• Explain what cellular respiration is.• Describe what happens during the
process of glycolysis and the Krebs cycle.
• Name the two main types of fermentation.
• Explain how high-energy electrons are used by the electron transport chain
• Compare photosynthesis and cellular respiration
Energy in our food
• One gram of glucose = 3811 calories of heat energy
• calorie – amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius
• Glycolysis – literally means “sugar splitting” in the presence of oxygen, glycolysis leads to two chemical pathways that produce energy
• AEROBIC – oxygen present• ANAEROBIC – no oxygen present
Cellular Respiration
• Sometimes called aerobic respiration• Process that releases energy by
breaking down glucose and other food molecules IN THE PRESENCE OF OXYGEN.
• 3 steps1. Glycolysis2. Krebs cycle3. Electron Transport Chain
The Equation
6O2 +C6H12O6 6CO2 + 6H2O + energy
Occurs in stages because cells must find a way to harvest the energy for later use.
1. Glycolysis• WHAT: Process by which 1 molecule of
glucose is broken in half producing 2 molecules of pyruvic acid.
• WHERE: Occurs in the cytoplasm• HOW: Uses 2 molecules of ATP – like an
investment in a savings account that pays back interest.
• At completion of glycolysis 4 ATP are made (but 2 were used) for a net gain of 2 ATP.
• Does NOT require oxygen – happens very quickly
• If oxygen is present we move on to the next step.
2. The Krebs Cycle
• WHAT: Pyruvic acid is broken down into carbon dioxide and releases energy.
• WHERE: Occurs in the mitochondrion• HOW: REQUIRES OXYGEN – AEROBIC• Carbon dioxide is released in your
breath• Involves the high energy electron
carriers NADH and FADH2
3. Electron Transport Chain
• WHAT: uses the high energy electron carriers from the Krebs Cycle to convert ADP to ATP.
• “Excited” electrons move down the chain producing 3 molecules of ATP on average.
The totals
• In the presence of oxygen: 36 total ATP are produced for each molecule of glucose.
Cellular Respiration
What happens if oxygen isn’t available?
• If Oxygen is not present after glycolysis different chemical pathways are followed – FERMENTATION
• 2 TYPES of fermentation– Alcoholic fermentation– Lactic Acid fermentation
Alcoholic Fermentation
• Occurs in yeast and a few other micro-organisms
• EQUATION:pyruvic acid +NADH alcohol +CO2 and
NAD+
Causes bread to rise. When the yeast runs out of oxygen it beginsto ferment – giving off bubbles of carbondioxide that form spaces in the bread Alcohol evaporates when baked.
Lactic Acid Fermentation
• Pyruvic acid accumulates and is converted to lactic acid.
• Produced in muscles when your body cannot supply enough oxygen and there is not enough ATP available.
• Causes painful burning sensations in your muscles.
• Unicellular organisms produce lactic acid as a waste which are used to make a variety of foods and beverages such as butter milk, yogurt, cheese , pickles, sour cream
• EQUATION: pyruvic acid +NADH lactic acid and
NAD+
Comparing Photosynthesis and Cellular Respiration
Photosynthesis Cellular Respiration
Function Energy capture Energy release
Location chloroplasts Mitochondrion
Reactants Carbon dioxide and water
Glucose and oxygen
Products Glucose and oxygen
Carbon dioxide and water
Equation