Photosynthesis

1
Photosynthesis

• Chapter 8

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Autotrophs vs. Heterotrophs

• Autotrophs Plants and some other types of
  organisms that use light energy from SUNLIGHT to
  make their own food. These organisms undergo
  photosynthesis!!
• EX Trees, grass, algae, plants
• Heterotrophs Organisms that CANNOT use the
  suns energy to make food they obtain enegry
  from the foods they consume
• EX Deer, rabbits, bear, fish, insects, etc

3
The Photosynthesis Equation

• Photosynthesis uses the energy of sunlight to
  convert water and carbon dioxide into high energy
  sugars and oxygen
• 6CO2 6H2O light?C6H12O6 6O2
• (carbon dioxide water light ? sugars
  oxygen)
• Plants then use the sugars to produce complex
  carbohydrates such as starches
• Plants obtain CO2 from the air or water in which
  they grow

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Photosynthesis
Light Energy
Chloroplast
CO2 H2O
Sugars O2
5
Inside a Chloroplast

• Chloroplast Filled with chlorophyll and are
  where photosynthesis takes place in plants and
  other photosynthetic eukaryotes
• Thylakoids saclike photosynthetic membranes
  arranged into stacks known as grana. Area where
  light-dependent reactions take place
• Photosystems clusters of chlorophyll and other
  pigments that are organized by the thylakoids
• Stroma Area outside the thylakoid membranes
  where light- independent reactions

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Light-dependent Reactions
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Figure 8-5 Chlorophyll Light Absorption
Section 8-2
Absorption of Light by Chlorophyll a and
Chlorophyll b
Chlorophyll b
Chlorophyll a
V
B
G
Y
O
R
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Electron Carriers

• Electron Transport The transfer of a pair of
  high energy electrons their energy to another
  molecule
• Electron Carriers The bucket or carrier that
  moves electrons and their energy from molecule to
  the next
• EX NADP Accepts and holds a pair of
  high-energy electrons and an H ion, converting
  NADP into NADPH turning energy from the sun into
  chemical energy .
• An analogy would be a pan carrying hot coals like
  the NADP carries two electrons and a H ion.

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ATP Formation
10
Adenosine Triphosphate (ATP)
Adenine
Ribose
3 Phosphate groups
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ADP and ATP (Electron Carriers)
ATP
ADP
Energy
Energy
Adenosine triphosphate (ATP)
Adenosine diphosphate (ADP) Phosphate
Partially charged battery
Fully charged battery
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Light-Dependent Reactions

• Light-Dependent Reactions Use energy from
  sunlight to produce the energy carriers ATP and
  NADPH and oxygen.
• Reactions occur within the thylakoid membranes
  of chloroplasts

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Light-dependent Reactions
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Figure 8-10 Light-Dependent Reactions
Section 8-3
Hydrogen Ion Movement
Chloroplast
Photosystem II
ATP synthase
Inner Thylakoid Space
Thylakoid Membrane
Stroma
Electron Transport Chain
Photosystem I
ATP Formation
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Photosynthesis
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Steps in Photosynthesis

• Photosynthesis Has five major steps that occur
  within the thylakoid membrane of the chloroplast
• 1. Photosystem II Light absorbed by
  photosystem II is used to break up water
  molecules into energized electrons, hydrogen ions
  (H) and oxygen.
• 2. Electron Transport Chain High-energy
  electrons from photosystem II move through the
  electron transport chain into photosystem I.

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Steps in Photosynthesis

• 3. Photosystem I Electrons released by
  photosystem II are energized again in photosystem
  I. Enzymes in the membrane use these electrons to
  make NADPH/
• 4. Hydrogen Ion Movement The inside of the
  tylakoid membrane is charged with H ions. This
  causes the outside of the thylakoid membrane to
  be negatively charged and the inside of the
  membrane to be positively charged.

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Steps in Photosynthesis

• 5. ATP Formation As hydrogen ions pass through
  ATP synthase, their energy is used to convert ADP
  into ATP. As it rotates ATP synthase (enzyme)
  binds ADP and P group to create ATP. Because of
  this, light-dependent transport produces high
  energy electron AND ATP.
• SUMMARY
• Light dependent reactions use water, ADP and
  NADP to produce oxygen, ATP and NADPH (Water,
  ADP, NADP Oxygen, ATP, NADPH)
• ATP and NADPH then provide energy to build energy
  containing sugars from low-energy compounds.

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Light-independent Reactions

• Calvin Cycle Energy stored in the ATP and NADPH
  formed during photosynthesis, is used to build
  high-energy sugars that can be stored for a long
  period of time.
• Does not require light and is called light
  independent reaction
• Takes place in the stroma of the chloroplasts

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Calvin Cycle
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Steps in the Calvin Cycle

• The Calvin Cycle has four major steps
• 1. C02 Enters the Cycle 6 CO2 molecules are
  combined with six 5- carbon molecules to produce
  three 12-carbon molecules
• 2. Energy Input Energy from ATP and electrons
  from NADPH convert the twelve 3-carbon molecules
  into higher-energy forms
• 3. 6-Carbon Sugar Produced two 3-carbon
  molecules are removed to produce sugars, lipids,
  amino acids, and other compounds

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Steps in the Calvin Cycle

• 4. 5-Carbon Molecules Regenerated the 10
  remaining 3-carbon molecules are converted back
  into six 5-carbon molecules, which are used to
  start the next cycle )

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Figure 8-11 Calvin Cycle
Section 8-3
CO2 Enters the Cycle
Energy Input
ChloropIast
5-Carbon Molecules Regenerated
6-Carbon Sugar Produced
Sugars and other compounds
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Concept Map
Section 8-3
Photosynthesis
includes
takes place in
uses
use
take place in
to produce
to produce
of
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Figure 8-7 Photosynthesis An Overview
Section 8-3
Chloroplast
Chloroplast
NADP
ADP P
Light- Dependent Reactions
Calvin Cycle
ATP
NADPH
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Factors Affect Photosynthesis

• Various Factors Affect the Rate of
  Photosynthesis.
• Some of these factors are
• 1. Amount of available water
• EX Plants in dry areas have waxy leaves to
  prevent water loss
• 2. Temperature
• EX Enzymes work best between 0 and 35C.
  Temps above or below this range may slow down
  photosynthesis or stop it entirely
• 3. Light Intensity
• 1. EX The higher the intensity the higher the
  rate of photosynthesis. There is a maximum limit
  however. This varies from plant to plant