Chapter 5
*Photosynthesis and Cellular Respiration
*Energy and Living Things
Section 5-1
* Where does energy in food come from?
*Directly or indirectly, all energy needed for metabolism comes from the SUN
*Energy enters living systems when plants, algae and bacteria absorb sunlight
*Some energy from the sun is captured to make organic compounds which are then stored
* Building molecules that store energy
*Metabolism either uses energy to build molecules or break down molecules that store energy
*Building molecules that store energy
*Photosynthesis is the process by which light energy is converted to chemical energy
*Autotrophs are organisms that use energy from sunlight or inorganic substances to make organic compounds
*Most autotrophs like plants are photosynthetic
*Breaking down food for energy
*Chemical energy in organic compounds can transfer to organisms that consume those compounds
*Heterotrophs are organisms that must get energy from food instead of directly from sunlight or inorganic substances
*Cellular respiration is a metabolic process where organisms harvest energy from food
* Cells Transfer energy from food to ATP
*Cells burn energy differently than wood burns
*In cells, stored energy is released in a series of enzyme assisted reactions
*When cells break down food molecules, some energy is released as heat, most is released as ATP
*ATP stores and Releases energy
*ATP (adenosine triphosphate) is a nucleotide with 2 energy storing phosphate groups
*Phosphate groups store energy like a spring and releases it when the bonds holding the groups together break
*ATP ADP + P + Energy
*PhotosynthesisSection 5-2
* Photosynthetic Organisms Use Sunlight’s Energy
*Plants, algae and some bacteria capture 1% of the energy in the sunlight that reaches Earth
*Photosynthesis Overview
*Stage 1: Energy is captured from sunlight
*Stage 2: Light energy is converted to chemical energy; stored as ATP and the energy carrier molecule NADPH
*Stage 3: Energy from ATP and NADPH powers the formation of organic compounds using carbon dioxide (CO2)
*6CO2 +6H2O C6H12O6+ 6O2Light
*Light Reactions
*First and second stage of photosynthesis are light stages
*Without light, these reactions would not occur
*Light energy is used to make energy storing compounds
* Pigments absorb different wavelengths of
light
*Pigments are molecules that absorb certain wavelengths of light and reflect others
*Chlorophyll is the primary pigment involved in photosynthesis and it absorbs red and blue and reflects green and yellow
*Carotenoids are pigments that produce yellow and orange fall leaf colors
*Using both carotenoids and chlorophyll absorbs more light energy, so plants use both
*Production of Oxygen
*Pigments used in photosynthesis are found in the chloroplast
*Clusters of pigments are embedded in disk-shaped structures called thylakoids
*When light strikes a thylakoid, energy is transferred to electrons in pigments and the electrons are excited
*Production of Oxygen cont…
*Excited electrons jump from pigment molecules to others and power second stage of photosynthesis
*The electrons must be replaced so water molecules split, taking electrons from hydrogen, leaving H+ and oxygen O which forms oxygen gas
*Cellular Respiration
Section 5-3
*Cellular Respiration Produces ATP
*Oxygen makes the production of ATP more efficient
*Some ATP is made without oxygen
*Metabolic processes that require oxygen are called aerobic
*Metabolic processes that do not require oxygen are called anaerobic
*Cellular Respiration
*Cellular respiration harnesses the energy in organic compounds
*C6H12O6 +602 6CO2 + 6H2O + energy
*Primary fuel for cellular respiration is glucose
*Glucose is formed when starch or sucrose are broken down
*Stage 1: Glucose is broken down
*Glucose (sugar) is broken down in the cytoplasm by the process glycolysis
*Glycolysis is an enzyme assisted anaerobic process that breaks down one 6-carbon molecule of glucose to two 3-carbon pyruvates
*Glycolysis uses 2 ATP molecules but produces 4 ATP molecules
*Glycolysis
*Step 1: Phosphate groups from 2 ATP molecules are transferred to glucose
*Step 2: The 6-carbon compound is broken down into two 3-carbon compounds + 1 Phosphate
*Step 3: Two NADH molecules are made 1 more phosphate group is added
*Step 4: Each 3 carbon compound is converted to 3-carbon pyruvates, which produces 4 ATP
*Stage 2: More ATP is made
*When oxygen is present, pyruvate from glycolysis enters a mitochondria and is converted to a 2 carbon compound
*This produces CO2, one NADH and a 2-carbon acetyl group
*This attaches to an enzyme A (CoA) making acetyl-CoA
*Acetyl-CoA enters a series of enzyme-assisted reactions called Krebs Cycle
*Krebs Cycle
*Step 1: Acetyl-CoA combines with a 4-C comp, making a 6-C comp and releasing CoA
*Step 2: CO2 is released from the 6-C comp forming a 5-C comp. e- transfer making NADH
*Step 3: CO2 is released from 5-C comp, making a 4-C, ATP and NADH
*Step 4: 4-C comp is converted to another, and e- transfer to make electron carrier, FADH2*Step 5: 4-C comp is converted to original 4-C comp, NADH is produced and cycle can start over
*Electron Transport Chain
*In aerobic respiration, electrons donated by NADH and FADH2 pass through electron transport chains
*The chain pumps H+ out of the mitochondria which combines with O2
to make H2O
*ATP is produced as H+ diffuses back into the mitochondria
*Fermentation Follows Glycolysis in Absence of Oxygen
*Without enough oxygen, Electron Transport Chain does not function the same
*O2 receives electrons and when not present, NADH and NAD+ cannot be recycled
*So NAD+ undergoes fermentation to recycle it
*Lactic Acid Fermentation
*Lactate is the ion of an organic acid called lactic acid
*A 3-C pyruvate converts to a 3-C lactate in order to continue glycolysis to produce ATP
*Alcoholic Fermentation
*3-C pyruvate is broken down to ethanol, a 2-C compound during alcoholic fermentation
*CO2 is released
*Electrons transfer from NADH to the 2-C compound producing ethanol
*NAD+ is recycled to continue glycolysis
*Comparing Anaerobic with Aerobic
*The total amount of ATP harvested from each glucose molecule depends on oxygen
*Cells use energy more efficiently when oxygen is present
*In stage 1: glucose is broken down by glycolysis (anaerobic) and gains 2 ATP
*In Stage 2: pyruvate passes thru aerobic respiration or (anaerobic) fermentation
*In fermentation, small amounts of ATP is produced
*In respiration, up to 2 ATP are produced by Krebs cycle and 34 through electron transport chains