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Cellular Respiration. Dr. Donna Howell Biology I Blacksburg High School. Cellular Respiration. Cellular respiration is the process by which living organisms take the sugar molecules that were made in photosynthesis, and convert them into energy for the organism.
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Cellular Respiration Dr. Donna Howell Biology I Blacksburg High School
Cellular Respiration • Cellular respiration is the process by which living organisms take the sugar molecules that were made in photosynthesis, and convert them into energy for the organism. • Although only plant cells undergo photosynthesis, ALL cells undergo cellular respiration.
Cellular Respiration • The chemical formula for cellular respiration is the exact opposite of the photosynthesis formula: • 6O2 + C6H12O6 • 6CO2 + 6H2O + energy • What this means is that six oxygen molecules react with a glucose molecule to form six carbon dioxide molecules and six water molecules and energy. • The energy released is used to produce approximately 34-36 molecules of ATP.
Glycolysis • Cellular respiration takes place in two steps: • Glycolysis • Krebs (citric acid) cycle OR fermentation
Glycolysis • When the glucose is broken down, the energy from the broken bonds are transferred to the ATP molecule. • This is called glycolysis.
Stage 1 • In stage 1, glycolysis, the glucose molecule is broken down into pyruvic acid and ATP molecules. • Glycolysis is a series of reactions using enzymes that take place in the cytoplasm of the cell.
Stage 2 • Two things could happen in Stage 2. • If oxygen is present, then what we call aerobic respiration takes place in the mitochondrion of the cell. • If oxygen is absent, then what we call anaerobic respiration takes place, such as fermentation.
Stage 2 – Aerobic Respiration • Takes place in mitochondria of cell. • First step is citric acid, or Krebs, cycle. • The pyruvic acid formed in glycolysis is chemically transformed, and releases carbon dioxide, water, and energy. • 2 ATP molecules are formed here.
Stage 2 – Aerobic Respiration • The next step is the electron transport chain. • This is a series of chemical reactions with hydrogen combining with oxygen to form water. Carbon dioxide is released as a waste product. • As many as 36 ATP molecules can be formed at the end of this cycle.
Stage 2 – Anaerobic Respiration • In the absence of oxygen, cells can obtain energy through the process of fermentation. • Fermentation is not an efficient process, yielding far fewer ATP molecules. • Two types: • Lactic acid fermentation • Alcohol fermentation
Stage 2 – Lactic Acid Fermentation • Lactic acid fermentation occurs when oxygen is absent, such as in muscle tissue during exercise. • It builds up in the muscle tissue, causing a burning, painful sensation.
Stage 2 – Lactic Acid Fermentation • The pyruvic acid formed during glycolysis is broken down to lactic acid, and in the process energy is released (used to form ATP).
Stage 2 – Alcohol Fermentation • This process occurs in yeasts and in some bacteria. • In this process, pyruvic acid formed during glycolysis is broken down to produce alcohol and carbon dioxide, and in the process energy is released (used to form ATP).
