CHAPTER 6 PHOTOSYNTHESIS

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CHAPTER 6PHOTOSYNTHESIS

• BIOLOGY LECTURE

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ENERGY FOR LIFE PROCESS

• All organisms
• require a constant supply
• of energy
• Energy does not recycle
• almost all energy is from
• the sun
• 3. Organisms capture the energy of light and
  store it in organic compounds

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ENERGY FOR LIFE PROCESS

• Classifying Organisms By How They Get Their
  Energy
• Autotrophs manufacture their
• own food from inorganic
• substances and energy
• Heterotrophs cannot
• manufacture their own
• organic compounds from
• inorganic substances

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AUTOTROPHS

• MAKE FOOD
• Use photosynthesis to convert light energy from
  the sun into chemical energy
• They store the chemical energy in organic
  compounds (carbohydrates)
• Examples are plants, algae, and cyanobacteria

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HETEROTROPHS

• Take in food
• They eat autotrophs or other heterotrophs
• A caterpillar (H) feeds on grass (A)
• A bird (H) feeds on the caterpillar (H)
• Examples are animals, most bacteria, fungi, and
  protozoa

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All fuel originates with the Autotrophs
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Energy Transfer Compounds

• Photosynthesis a biochemical pathway that
  converts solar energy to chemical energy (STORE
  ENERGY FOOD)
• Autotrophs manufacture organic compounds from
  carbon dioxide and water and oxygen is released
• 6CO2 6H2O LIGHT C6H12O6 6O2

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How Do We Get Energy?

• Cellular Respiration A biochemical pathway
  that breaks down chemical energy for use by the
  cell (RELEASE ENERGY)
• In both autotrophs and heterotrophs, organic
  compounds are combined with oxygen to produce
  ATP, carbon dioxide and water
• C6H12O6 6O2 6CO2 6H2O ENERGY
  (ATP)

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Energy Transfer Compounds

• Adenosine Triphosphate molecule of stored
  energy
• Energy stored in bonds between phosphate
  (A M P P P)
• AMP, ADP, ATP
• Nicotinamide Adenine Dinucleotide Phosphate -
  molecule that transports energy
• NADP to NADPH

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Do Now

• 1. What is the difference between autotrophs and
  heterotrophs?
• 2. What is photosynthesis?
• 3. What is cellular respiration?
• 4. What are the 2 energy transfer compounds we
  talked about?

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LIGHT ABSORPTION IN CHLOROPLASTS

• Chloroplasts - membrane bound organelles that
  contain
• 1. the pigment chlorophyll
• 2. enzymes for photosynthesis
• Both light and dark reactions take place here

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Chloroplasts

• Inner/outer membrane
• Thylakoids flattened sacs where photosynthesis
  takes place
• Granum (pl. grana) stack of thylakoids
• Stroma liquid solution that surrounds the
  thylakoids

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CHLOROPLASTS IN PLANT CELL
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Light

• A. White light composed of visible spectrum
• ROY G BIV
• B. Light travels in energy waves
• C. Wavelength (?) determines color of light
• D. UV ? violet ? red
• Short ? ? Long ?
• E. Pigment compound that absorbs light
• F. Ex. Green pigment absorbs colors other than
  green reflects/transmits green

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Chloroplast Pigments

• There are several different
• pigments in the thylakoid
• membranes
• Chlorophyll is a pigment
• that absorbs red and blue
• light and reflects green light
• Chlorophyll a is directly involved with the light
  reaction

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Chloroplast Pigments

• Accessory pigments trap wavelengths of light that
  can not be absorbed by chlorophyll a (help
  capture more light)
• a. Chlorophyll b also reflects green, but
  absorbs more blue than red
• b. Carotenoids reflect orange, yellow, and
  brown and absorbs green and blue
• c. Phycobilins reflect violet blue and
  absorb orange, brown and green

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Do Now

• 1. What important process occurs in chloroplasts?
• 2. What are the flattened sacs in chloroplasts
  called?
• 3. What is a pigment and what important pigment
  is found in the chloroplast?

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Electron Transport Chain (ETC)

• Photosystem a cluster of pigment molecules found
  in the thylakoid membrane
• 2 Photosystems each has different roles in
  photosynthesis
• Photosystem I
• Photosystem II

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Electron Transport Chain (ETC)

• Light Reaction Photosystem II
• 1. Light energy absorbed by pigments and
  transferred to chlorophyl a . Electron from
  chlorophyl a gets excited enters a higher
  energy level
• 2. Electron leaves chlorophyl a enters
  primary e- acceptor
• 3. Primary e- acceptor transfers e- to series
  of molecules (electron transport chain) loses
  Energy (E used to move p into thylakoid)

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Electron Transport Chain (ETC)

• Light Reaction Photosystem I
• 4. Light is absorbed by photosystem I, electrons
  move from chlorophyll a molecules to another
  primary electron acceptor. These e- are replaced
  with those from photosystem II
• 5. e- used to make NADPH from NADP (NADP
  H ?NADPH)

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Waters role

• e- from splitting of H2O replaces lost e- in
  photosystem II
• 2 H2O ? 4 H 4 e- O2
• O2 leaves plant or used for cellular respiration
• H stays in thylakoid ? concentration gradient

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Electron Transport Chain
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E. Biochemical pathways series of
biochemical reactions
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Chemiosmosis - Make ATP

• Concentration gradient causes protons (H) to
  move from thylakoid (high conc) to stroma (low
  conc)
• ATP synthase uses movement of protons/change in
  potential energy to make ATP
• Converts potential E to chemical E
• ATP synthase (multifunctional protein)
• Carrier protein carries protons across
  thylakoid membrane
• Enzyme catalyzes synthesis of ATP from ADP

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Calvin cycle

• Uses ATP NADPH from the light reaction as
  energy to make organic compounds
• Carbon from CO2 fixed into organic compounds
• Each cycle uses 3 ATP 2 NADPH
• Occurs in stroma of chloroplast
• Called the Dark Reaction

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Photosynthesis Balance Sheet

• 3 turns of the Calvin Cycle are required to
  produce each molecule of PGAL
• This uses up 9 molecules of ATP and 6 molecules
  of NADPH
• Most of the molecules made in the Calvin Cycle
  are built up into
• Amino Acids
• Lipids
• Carbohydrates
• Heterotrophs use the energy in these organic
  compounds for living

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Photosynthesis Equation

• 6CO2 6H2O Light Energy C6H12O6 6O2

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Do Now

• 1. What is a photosystem?
• 2. What is the electron transport chain?
• 3. What is the purpose of the Calvin cycle?
• 4. What is the equation for photosynthesis?

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C3 Plants Alternative Pathways

• Plants that use Calvin cycle are called C3 plants
  because they fix CO2 into a 3C compound PGA
• Stomata (pl.) - small pores on the underside of a
  leaf where water, CO2, and O2 pass through
• Plants can partially close stomata to minimize
  water loss
• Plants open stomata during day close _at_ night

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C3 Plants Alternative Pathways

• When stomata close up, CO2 cant get into the
  plant and O2 cant get out of the plant
• This inhibits carbon fixation by the Calvin Cycle
  in the plant
• Plants have to find other ways
• to fix carbon and make food

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C4 Plants

• Partially close stomata during hottest part of
  day
• Certain cells have enzymes that can fix CO2 into
  4C compound even when CO2?, O2?
• Lose ½ the amount of water as C3 plants but
  produce the same amount of carbs
• Ex. Corn, sugar cane, crab grass

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CAM Plants

• Open stomata _at_ night
• close during day
• B/C of this CO2 enters when colder ? slower
  growth, less water loss
• Fix CO2 into a variety of diff. C comp.
• at night, use for Calvin Cycle during day
• Cactuses, pineapple, and others with different
  adaptations to hot climate

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Rate of Photosynthesis

• Effected by the Environment
• Light Intensity as light increases rate of
  photosynthesis increases and then levels off when
  available electrons are already excited
• CO2 as CO2 levels increase rate of
  photosynthesis increases and then levels off
• Temperature raising the temp. speeds up
  chemical reactions and increases the rate of
  photosynthesis, but soon the temp gets too high
  and photosynthesis rate decreases

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Rate of photosynthesis

• 1. Light, CO2 eventually level off _at_ maximum
• 2. Temperature reach a maximum decrease
• Enzymes begin to become unstable ineffective
• Stomata close limit water loss CO2 entry

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Cellular Respiration

• Chapter 7

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Cellular Respiration Overview

• A. Releases energy from organic molecules
  (sugars) to make ATP (available cell energy)
• B. Done by autotrophs and heterotrophs
• C. Aerobic respiration organic molecules broken
  down with oxygen yields a lot of ATP
• D. Anaerobic respiration organic molecules
  broken down without oxygen little or no ATP.
• E. Living organisms could specialize in one, or
  switch depending on available oxygen.

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• Glycolysis
• All organisms begin respiration with glycolysis
  (to break glucose) small amount of energy (net
  2 ATP produced), but makes energy carrying
  (electron) molecule NADH and pyruvic acid
  (organic product)
• Anaerobic in nature
• Products can either be fermented (recycle NADH)
  or aerobically broken (lots of ATP)
• Takes place in cytoplasm
• Reactions in the biochemical pathway

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Glycolysis

1. 2 phos. groups attach to glucose from 2 ATPs to
   form a new 6 C compound
2. 6 C comp. splits into 2 PGAL molecules (3 C)
3. 2 phos. groups attach to PGALs and PGALs
   oxidized. NAD reduced to NADH.
4. Phos. groups removed and combine with ADPs ? ATP.
   2 pyruvic acid molecules formed.

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Do Now

• 1. What is cellular respiration?
• 2. What is anaerobic respiration?
• 3. What is aerobic respiration?
• 4. What is glycolysis?

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Fermentation

• Performed in the absence of oxygen
• Makes no ATP, occurs in cytoplasm
• Regenerates NAD which can keep glycolysis going
• Types
• 1. Lactic Acid
• 2. Ethyl alcohol

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Lactic Acid Fermentation

• Enzyme converts pyruvic acid into lactic acid
• Some bacteria fungi do this ? yogurt,
• cheese
• Animal cells (Muscle cells w/o oxygen)

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Lactic Acid Fermentation

• Occurs when you are
• exercising strenuously
• Muscle cells use up oxygen
• faster than you can breathe it in
• Muscle cells switch from aerobic respiration to
  lactic acid fermentation
• Can make muscles sore and cause cramping
• Eventually the lactic acid gets turned back into
  pyruvate in the liver

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Alcoholic Fermentation

• Plants and yeast
• Pyruvic acid is broken down and a CO2 is removed,
  the resulting 2C compound is ethyl alcohol.

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Alcoholic Fermentation

• The basis of the beer
• and wine industry
• Yeast cells are added
• to either crushed grapes
• or grains
• They perform fermentation to produce ethyl
  alcohol
• Regular wine CO2 is released
• Beer and champagne CO2 is retained

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Anaerobic Energy Yield

• When glucose is broken down anaerobically, only 2
  ATPs are produced during glycolysis
• Most of the energy is still trapped in the
  pyruvic acid
• The efficiency of energy transfer is very low at
  3.5
• This is OK for small, unicellular organisms, but
  larger organisms need more energy!!

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Do Now

• 1. Is fermentation done in the presence or
  absence of oxygen?
• 2. What are the 2 types of fermentation we talked
  about?
• 3. Is fermentation efficient for energy transfer?
  

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Aerobic Respiration

• If oxygen is present, pyruvic acid goes from
  glycolysis to aerobic respiration
• Aerobic respiration produces 20 X as much ATP
• 2 major stages
• 1. Krebs Cycle small amount of ATP
• 2. Electron transport chain large amount of ATP

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Aerobic Respiration

• Occurs in mitochondria of eukaryotes (cytoplasm
  in prokaryotes)
• Outer membrane
• Inner membrane (cristae folds)
• Matrix inside inner membrane contains enzymes
  needed to catalyze the Krebs Cycle

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Coenzyme A/Acetyl CoA

• 1. As Pyruvic acid enters the mitochondrial
  matrix it bonds with Coenzyme A (CoA) and
  produces CO2 Acetyl CoA
• a.NAD ? NADH
• 2. Acetyl CoA begins the Krebs cycle

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Krebs CycleBreaks down Acetyl CoA producing
CO2, H atoms, and ATP

• 1. Acetyl CoA rxts w/ oxaloacetic acid ? CoA
  citric acid
• 2. 1 glucose does 2 cycles
• 3. Krebs cycle produces 2 CO2, 3 NADH, 1 FADH2
  and 1 ATP per cycle
• (x2 b/c 2 cycles)
• 4. NADH FADH2 used in ETC

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Energy So Far

• Bulk of the energy released by the oxidation of
  glucose is still not in form of ATP
• This will require the NADH and FADH2 that we have
  made so far
• Glycolysis 2 NADH
• Convert Pyruvic Acid to Acetyl CoA 2 NADH
• Krebs Cycle 6 NADH, and 2 FADH2
• These 10 NADH and 2 FADH2 molecules will enter
  the electron transport chain and make ATP

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Electron Transport Chain

• 1. Electrons for the ETC are supplied by the
  splitting of NADH and FADH2
• 2. Protons from NADH and FADH2 are pumped through
  the inner mitochondrial membrane away from the
  matrix by the ETC
• 3. The pumping of protons across the membrane
  creates a conc. gradient which is then used to
  make ATP by ATP synthase.
• 4. Final e- acceptor is O2. (H20 is produced)

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Electron Transport Chain
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Energy

• 1. Converted in the ETC
• a. 1 NADH 3 ATP
• b.1 FADH2 2 ATP
• 2.
• a. 38 ATP (12 kcal)/Glucose (686 kcal)
• b. Aerobic Efficiency 66

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Respiration Equation

• C6H12O6 6O2 6CO2 6H2O Energy
• This equation is the opposite of the equation for
  Photosynthesis!

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