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Photosynthesis and Cellular Respiration. Objectives Section 1. I can explain in detail the flow of energy through living systems I can compare the chemical processes of autotrophs and heterotrophs I can describe the role of ATP in metabolism I can describe how energy is released by ATP.

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Photosynthesis and Cellular Respiration

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objectives section 1
Objectives Section 1
  • I can explain in detail the flow of energy through living systems
  • I can compare the chemical processes of autotrophs and heterotrophs
  • I can describe the role of ATP in metabolism
  • I can describe how energy is released by ATP.

Metabolism: all of the chemical reactions that take place within an organism

  • Metabolic pathways alter molecules in a series of steps.
  • Enzymes selectively accelerate each step.
    • enzymes are regulated to maintain a balance of supply and demand.
Catabolic reactions give off energy by breaking down complicated molecules to simpler compounds.
  • Anabolic reactions useenergy to build complicated molecules from simpler compounds.
  • The energy released by catabolic pathways is used to drive anabolic pathways.
autotrophs vs heterotrophs
Autotrophs vs Heterotrophs
  • Autotrophs make their own food through anabolic reactions
    • Many autotrophs carry out photosynthesis
  • Heterotrophs can not make their own food
    • Heterotrophs must eat other organisms to obtain energy from food through catabolic reactions
    • Heterotrophs utilize cellular respiration
  • ATP powers cellular work
  • A cell does three main kinds of work:
    • Mechanical work, beating of cilia, contraction of muscle cells, and movement of chromosomes
    • Transport work, pumping substances across membranes against the direction of spontaneous movement
    • Chemical work, driving endergonic reactions such as the synthesis of polymers from monomers
ATP (adenosine triphosphate) is a type of nucleotide consisting of the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups.
so what
So what?
  • Energy is stored in these bonds.
  • So?
  • The breaking of the chemical bond releases the energy


cellular respiration
Cellular Respiration
  • The process by which mitochondria break down glucose to make ATP
  • In order for our bodies to use the energy, the food must be broken down into a usable form
    • What is the usable form of energy?
    • What type of process breaks down molecules?
objectives section 3 yes we skipped to section 3 for now
Objectives Section 3 (yes, we skipped to section 3, for now)
  • I can summarize how glucose is broken down in glycolysis.
  • I can describe how ATP is made in cellular respiration.
  • I can identify the role of fermentation in cellular respiration.
  • I can evaluate the importance of oxygen in aerobic respiration.
overall reaction
Overall Reaction

C6H12O6 + 6O2→ 6CO2 + 6H2O + 38 ATP

  • Overall this is a three stage process
  • Glycolysis:
    • Occurs in the cytoplasm
    • Glucose is broken down
  • Krebs Cycle
    • Breaks down pyruvate into CO2
    • Occurs in mitochondrial matrix
  • Electron Transport Chain
    • ATP is synthesized
  • Glyco = glucose Lysis = break down
  • Occurs in the cytoplasm
  • This stage occurs in BOTH aerobic and anaerobic respiration
  • Glucose breaks down into 2 pyruvate (2 ATP are also made)
    • Glucose is a 6-carbon sugar
    • Pyruvate is a 3-carbon molecule (there are two of them)
    • See diagram on simple explanation handout
glycolysis reactants and products

1 glucose

Enzymes are needed

2 ATP are needed to start


2 Pyruvates (go to next step)

4 ATP (2 are gained)

2 NADH (go to ETC)

Glycolysis Reactants and Products
intermediate step
Intermediate step
  • Pyruvate is converted to acetyl CoA
  • Occurs in the cytoplasm
  • See diagram on simple explanation handout
intermediate step reactants and products
Intermediate step Reactants and products


  • 2 pyruvate (from glycolysis)


  • 2 Acetyl CoA (go to next step)
  • 2 CO2 (given off as waste)
  • 2 NADH (go to ETC)
krebs cycle citric acid cycle
Krebs Cycle (Citric Acid Cycle)
  • Occurs in the matrix of mitochondria
  • A series of reactions occur (this is not just one step)
  • Main purpose is to generate electrons for use in ETC
  • 2 ATP is given off
  • See diagram on simple explanation handout
krebs cycle reactants and products
Krebs Cycle Reactants and Products


  • 2 Acetyl CoA


  • 2 ATP
  • 6 NADH (go to ETC)
  • 2 FADH2 (go to ETC)
  • 4 CO2 (given off as waste)
electron transport chain
Electron Transport Chain
  • Occurs in inner membrane of mitochondria
  • Series (chain) of coupled redox reactions (electrons are transported through the chain)
  • Electrons carried to this step by NADH and FADH2 (produced in previous steps)
  • Oxygen is used in this step
  • Water is given off
electron transport chain reactants and products
Electron Transport Chain Reactants and Products


  • 10 NADH
  • 2 FADH2
  • Oxygen


  • 34 ATP
  • H2O
where do we get 38 atp
Where do we get 38 ATP?
  • 2 ATP made in glycolysis
  • 2 ATP made in Krebs Cycle
  • 34 ATP made in ETC
    • 1 NADH = 3 ATP
      • 10 X 3 = 30
    • 1 FADH2 = 2 ATP
      • 2 X 2 = 4
anaerobic respiration fermentation
Anaerobic Respiration (Fermentation)
  • Glycolysis
  • Yields 2 pyruvate and 2 ATP
  • With no oxygen present, cellular respiration does not occur
  • ONLY 2 ATP ARE PRODUCED (compare to aerobic respiration)
two types of fermentation
Two Types of Fermentation

Alcoholic Fermentation

  • Pyruvate converted to ethyl alcohol and CO2
  • Carried out by yeast and some bacteria
  • Used in producing alcohol (both consumable and for ethanol), and for baking

Lactic Acid Fermentation

  • Pyruvate converted to lactic acid
  • Carried out by muscles when working hard (muscles need ATP but can’t get O2 )
  • Causes muscle soreness and cramps
  • Carried out by most (not all) autotrophs
  • 6CO2 + 6H2O + light energy→ C6H12O6 + 6O2
  • Basically this reaction is the OPPOSITE of cellular respiration
  • See simple explanation handout and text
steps of photosynthesis
Steps of Photosynthesis
  • Light reaction (depends on light)
    • Traps sunlight
    • Produces electrons and ATP required to power the dark reaction
    • Oxygen given off here
  • Dark reaction, aka Calvin Cycle (does not directly depend on light)
    • Uses ATP and electrons from light reaction and CO2 to make glucose

See diagram on simple explanation handout