Chapter 9: 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 steps 1. Glycolysis 2. Krebs cycle 3. Electron Transport Chain

The Equation 6O 2 +C 6 H 12 O 6 6CO 2 + 6H 2 O + 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 FADH 2

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. 2 from Glycolysis 34 from the Krebs cycle and ETC.

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 +CO 2 and NAD + Causes bread to rise. When the yeast runs out of oxygen it begins to ferment – giving off bubbles of carbon dioxide 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 wich 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 PhotosynthesisCellular Respiration FunctionEnergy captureEnergy release LocationchloroplastsMitochondrion ReactantsCarbon dioxide and water Glucose and oxygen ProductsGlucose and oxygen Carbon dioxide and water Equation