Cellular Respiration

Chemical Energy and Food Food provides living things with the chemical building blocks they need to grow and reproduce. Food is a source of energy

Chemical Energy and Food One gram of the sugar glucose (C 6 H 12 O 6 ) when burned in the presence of oxygen is 3811 calories of heat energy Calorie – amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius The calorie on a food labels is a kilocalorie, or 1000 calories

Chemical Energy and Food Cells gradually release the energy from glucose beginning with the process of glycolysis Glycolysis leads to different pathways depending on whether oxygen is present or not

Overview of Cellular Respiration In the presence of oxygen, glycolysis is followed by the Krebs cycle and the electron transport chain These three processes together are called cellular respiration Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen

Overview of Cellular Respiration Oxygen + glucose ---> carbon dioxide + water + energy O 2 + C 6 H 12 O 6 ---> CO 2 + H 2 O + energy 6O 2 + C 6 H 12 O 6 ---> 6CO 2 + 6H 2 O + energy Notice that this is the reverse of photosynthesis!

Overview of Cellular Respiration Cellular respiration occurs in a series of steps or all of the energy in glucose would be released at one time This energy would be wasted as light and heat Cellular respiration occurs in three main stages: glycolysis, Kreb's Cycle, and electron transport chain

Fermentation When oxygen is not present, glycolysis is followed by a different pathway, fermentation Fermentation – releases energy from food molecules by producing ATP is the absence of oxygen Fermentation is an anaerobic process Anaerobic – without oxygen Aerobic – with oxygen

Fermentation The two main types of fermentation are alcoholic fermentation and lactic acid fermentation Alcoholic fermentation produces ethyl alcohol and carbon dioxide

Fermentation Lactic acid fermentation produces lactic acid Lactic acid is produced in your muscles during rapid exercise when the body can not supply enough oxygen to the tissues The buildup of lactic acid causes a painful burning sensation This is why muscles feel sore after intense activity

Fermentation Lactic acid fermentation is used to produce cheese, yogurt, buttermilk, sour cream, pickles, sauerkraut, and many other foods and beverages

Comparing Photosynthesis and Cellular Respiration The energy flows in photosynthesis and cellular respiration take place in opposite directions An analogy: – The chemical energy in carbohydrates is money in a savings account – Photosynthesis is the process that “deposits” energy – Cellular respiration is the process that “withdraws” energy

Comparing Photosynthesis and Cellular Respiration Photosynthesis and cellular respiration are complete opposites Photosynthesis buts oxygen into the air; cellular respiration removes it Photosynthesis uses water; cellular respiration produces water