Ch. 8-9: Photosynthesis and Respiration

• Photosynthesis
  
• Energy and Life
  
  • autotrophs - make their own food, heterotrophs cannot
    
  • Chemical Energy and ATP
    
    • energy molecule used by cells = ATP (adenosine triphosphate)
      
    • to store energy, cells bond phosphate to a molecule called ADP (adenosine diphosphate) to form ATP
      
    • to release energy, the cell removes the phosphate from ATP to form ADP and phosphate, the released energy is used in cellular processes
      
• Photosynthesis
  
  • plants convert the energy of sunlight into the energy in the chemical bonds of sugars and starches
    
  • History of Research
    
    • Jan Van Helmont - 17th century, found that a willow sprig grew 75 kg into a tree while the soil lost almost no mass, he concluded the mass gain was from water
      
    • Joseph Priestly - 18th century, found that plants renew the air in a jar with a candle that had depleted the air in the jar
      
    • Jan Ingenhousz showed that the renewing process only occurred in the presence of light
      
  • the equation for photosynthesis is:
    
    • 6 CO₂ + 6 H₂O ----> C₆H₁₂O₆ + 6 O₂
      
    • the equation states that carbon dioxide and water are used (in the presence of light) to produce carbohydrate and oxygen
      
  • sunlight
    
    • autotrophs can carry out photosynthesis, heterotrophs cannot and must absorb or eat foods
      
    • the white light of sunlight is actually a mixture of the colors red, orange, yellow, green, blue, violet
      
    • each color differs from the others by its wavelength
      
  • pigments
    
    • are colored substances that absorb and reflect light
      
    • chlorophyll is the main pigment of photosynthesis
      
    • chlorophyll absorbs red, orange, blue, violet well
      
• Photosynthesis: The Light and Dark Reactions
  
  • Inside a Chloroplast
    
    • contain small interconnected disks called thylakoids
      
    • proteins and pigments on the thylakoids form photosystems for capturing light
      
    • the fluid around the thylakoids is called the stroma
      
  • Electron Carriers
    
    • light striking chlorophyll raises electrons to new energy states
      
    • the electrons are moved to other chemicals called electron acceptors
      
    • NADP⁺ accepts electrons to become NADPH
      
  • The Light-Dependent Reactions
    
    • produce oxygen gas and convert ADP and NADP⁺ to ATP and NADPH
      
    • captures the energy of sunlight to make energy storing compounds
      
    • take place on the photosynthetic membranes within the chloroplast (thylakoids)
      
    • uses two groups of pigments: photosystem I and photosystem II
      
    • PII transfers electrons to PI which transfers them to NADP
      
    • PII gets its electrons from the splitting of water, which releases oxygen gas
      
    • as the electrons move between the photosystems, ATP is made from their energy (via the hydrogen ion pool that is pumped by the moving electrons)
      
  • The Calvin Cycle (Dark Reactions)
    
    • uses ATP and NADPH to produce high energy sugars
      
    • carbon dioxide is combined with a 5 carbon sugar to form two 3 carbon sugars
      
    • the 3 carbon sugars that are made are used to make more 5 carbon sugars and glucose, using the ATP and NADPH from the light reactions
      
  • Factors Affecting Photosynthesis
    
    • water shortages, cold temperatures, and low light intensity all slow photosynthesis
      
      
• Respiration
  
• Chemical Pathways
  
  • food provides the building blocks and energy for living things to grow
    
  • Chemical Energy and Food
    
    • one gram of glucose releases 3811 calories of heat
      
    • one calorie = amount of heat required to raise one gram of water by one degree celsius
      
    • glycolysis begins the cellular respiration pathway in cells
      
    • Overview
      
      • glycolysis, krebs cycle, electron transport system = cellular respiration
        
      • the equation for aerobic respiration is:
        
        • C₆H₁₂O₆ + 6 O₂ ----> 6 CO₂ + 6 H₂O
          
        • the reaction releases 3811 calories/g glucose
          
• Glycolysis and Respiration
  
  • Glycolysis - Breaking Down Glucose
    
    • glycolysis splits glucose in half, into 2 molecules of pyruvate
      
    • ATP are required to start glycolysis (2 per glucose)
      
    • ATP are produced by glycolysis (4 per glucose) by using some of the energy released to bond ADP and P
      
    • hydrogen atoms are released to NAD (coenzyme that carries hydrogen to mitochondria)
      
  • Fermentation
    
    • when cells are deprived of oxygen, they respire anaerobically
      
    • anaerobic respiration involves the dumping of hydrogen atoms (electrons) of NADH on pyruvate or another inorganic compound, producing NAD⁺
      
    • this allows glycolysis to continue, breaking down glucose to pyruvate and releasing a few ATP for cellular glucose per glucose used
      
    • Alcoholic Fermentation
      
      • NADH + pyruvate ---> NAD⁺ + alcohol + CO₂
        
      • the carbon dioxide that is produced is used to make bread rise and wine bubble
        
      • at 12%, the yeast die from alcohol poisoning
        
    • Lactic Acid Fermentation
      
      • NADH + pyruvate ----> NAD⁺ + lactic acid
        
      • lactic acid is believed to cause muscle soreness when muscles are overused in strenuous exercise
        
  • The Krebs Cycle and Electron Transport
    
    • is aerobic, requires oxygen, occurs in the mitochondrion, breaks down food to release energy
      
    • the released energy enters the ATP cycle
      
    • The Krebs Cycle
      
      • takes place in the mitochondrion, 1st documented in 1937 by Hans Krebs
        
      • takes pyruvate (from glycolysis) and breaks it down to carbon dioxide and hydrogen atoms
        
      • the hydrogen atoms are picked up by NAD and FAD
        
      • it is a cycle because it produces a compound it starts with
        
    • Electron Transport in the Mitochondrion
      
      • proteins in the inner mitochondrial membrane receive the hydrogen atoms and pass their electrons along
        
      • as the electrons pass along, their energy is used to bond P and ADP to form ATP, which can then be used by cellular organelles
        
      • oxygen is needed at the end of the electron transport chain to remove the electrons from the chain
        
    • ATP Formation
      
      • the moving electrons on the chain actually pump hydrogen ions which are used to make the ATP
        
    • The Totals
      
      • a maximum of about 38 ATP are hypothetically made from one glucose, but the actual yield is lower, probably around 23
        
    • Obtaining Energy From Food
      
      • complex carbohydrates are broken down into simple sugars, converted to glucose, and used in glycolysis
        
      • proteins are digested to amino acids which can be converted to compounds that are used by the Krebs cycle
        
      • fatty acids are broken down to compounds used by the Krebs cycle
        
    • Energy and Exercise
      
      • breathing takes place to feed oxygen to the mitochondria of the body, and to rid of carbon dioxide coming out of the mitochondria
        
      • intense short-term exercise can be powered by glycolysis if oxygen is unavailable
        
      • long-term exercise (over 90 seconds) requires cellular respiration - an aerobic process
        
    • Comparing Photosynthesis and Cellular Respiration
      
      • photosynthesis and respiration are opposite processes
        
      • one deposits energy while the other withdraws energy from biochemicals