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