Cell Energy Chapter 4

Energy and Living Things A. Autotrophs – produce their own food B. Heterotrophs – get food from somewhere else (what they eat)

C. ATP (adenosine triphosphate) 1. When food is “burned”… a C. ATP (adenosine triphosphate) 1. When food is “burned”… a. Some of the energy is “lost” as heat (not useful) b. Some of the energy is stored in molecules of ATP – ready to use energy

a. Main molecule plus a phosphate “tail” - 2. Structure of ATP a. Main molecule plus a phosphate “tail” b. Phosphates are negative  repel each other  unstable c. ATP  ADP (di = two) + phosphate (Bond broken…energy RELEASED) d. ADP + phosphate  ATP (Bond formed…energy STORED)

Photosynthesis A. Plants convert the energy of sunlight into the energy stored in glucose (chemical energy)

B. Early Experiments in Photosynthesis 1. Jan Van Helmont a. Found the mass of a pot of soil... planted a seedling…allowed plant to grow for 5 years…mass of soil was unchanged b. Van Helmont said mass came from H2O (incorrect conclusion) c. Mass actually comes from CO2

2. Joseph Priestly – Experiment with glass jar, candle, plant & mouse a. What is being produced by the plant? Oxygen!

C. Photosynthesis Overview 1. Reactants: carbon dioxide & water 2. Another requirement: sunlight 3. Products: glucose (a monosaccharide) and oxygen 4. Equation: (with sunlight) 6CO2 + 6H2O  C6H12O6 + 6O2

5. Photosynthesis also requires pigments – colored substances that absorb light energy so it can be used for photosynthesis a. Chlorophyll – absorbs red and blue light best; reflects green (that’s why plants are green!) b. Carotenoids – absorbs different colors than chlorophyll; reflects yellow and orange (fall colors!)

D. The “Light Reactions” (Also called the Light-Dependent Reactions) 1. Energy in light is captured by pigments & (with the help of H2O) is used to make ATP 2. NADPH (another energy molecule) is also made – both ATP & NADPH will be used in the dark reactions 3. Occurs in the thylakoids of chloroplasts (chlorophyll is in here) 4. Oxygen produced as a waste product

E. The “Dark Reactions” (Also called Light-Independent Reactions or Calvin Cycle) 1. Light is not needed 2. ATP, NADPH (from light rxns) and CO2 are used to make glucose 3. Called carbon fixation – transfer of carbon from CO2 (inorganic) into glucose (organic) 4. Why called the Calvin Cycle? Named after the man who identified the reactions (Melvin Calvin – Nobel Prize 1961)

Cellular Respiration A. Organism gets food by eating or using photosynthesis to make glucose (which stores energy) B. Cellular respiration releases that energy by breaking down food and converting stored energy into ATP (ready to use!) C. Equation: C6H12O6 + 6O2  6CO2 + 6H2O + 36 ATP

D. Glycolysis (Always occurs before cellular respiration) 1. Takes place in the cytoplasm 2. Anaerobic – no oxygen needed 3. What is the process? a. Using 2 ATP, glucose is broken in half  2 pyruvate molecules b. 4 ATP produced (net ATP = 2)

E. Process of Cellular Respiration 1. Includes two steps: Krebs Cycle (Step 1) and Electron Transport (Step 2) 2. Takes place in mitochondria 3. Aerobic – oxygen is needed 4. Cellular respiration starts out using the pyruvate formed in glycolysis - Pyruvate must move from cytoplasm into mitochondria

4. Events during Cellular Respiration a 4. Events during Cellular Respiration a. Pyruvate is broken down - Each time a bond is broken, the energy released is used to make ATP! b. Carbon dioxide and water are produced as waste products c. 34 ATP produced (34 + 2 ATP from glycolysis = 36 ATP total)

F. At the end of cellular respiration… 37% of the energy in glucose has been used by cells (put into ATP) • This is actually very efficient…much more efficient than cars burning gasoline (14 – 26%)

G. How do photosynthesis and cellular respiration relate? 1. Opposite processes • Photosynthesis “deposits” money or energy • Respiration “withdraws” money or energy

So… What’s going on?

Fermentation A. Why is fermentation necessary? 1. Respiration requires what important gas? Oxygen 2. What happens when oxygen is not available? Fermentation 3. If oxygen is not required for fermentation, it is…anaerobic 4. Fermentation does NOT make ATP, but it does allow glycolysis to continue (so we get at least 2 ATP)

B. Lactic Acid Fermentation 1. Pyruvate from glycolysis is converted into lactic acid 2. Occurs in muscles during rapid exercise • Body cannot supply enough oxygen to the muscle tissues to produce all of the ATP needed • Lactic acid fermentation is used • Buildup of lactic acid in muscles…burning sensation

C. Alcoholic Fermentation 1. Occurs in yeasts and a few other microorganisms 2. Pyruvate is broken down to produce alcohol and CO2 3. Important to bakers & brewers

Putting it all together…