Photosynthesis

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Photosynthesis

• most important chemical process on Earth
• It provides food for virtually all organisms
• Photos light
• Synthesis to put together
• Puts together a sugar molecule using energy from
  light

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AN OVERVIEW OF PHOTOSYNTHESIS

• Photosynthesis is the process by which
  autotrophic organisms use light energy to make
  sugar and oxygen gas from carbon dioxide and
  water

PHOTOSYNTHESIS
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Autotrophs are the producers of the biosphere
They are the ultimate producers of food consumed
by virtually all organisms
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Photosynthesis occurs in chloroplasts

• In most plants, photosynthesis occurs primarily
  in the leaves, in the chloroplasts
• A chloroplast contains
• stroma, a fluid
• grana, stacks of thylakoids
• The thylakoids contain chlorophyll
• Chlorophyll is the green pigment that captures
  light for photosynthesis

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The location and structure of chloroplasts
MESOPHYLL CELL
LEAF CROSS SECTION
LEAF
CHLOROPLAST
Granum
Stroma
Thylakoid
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Plants produce O2 gas by splitting water

• The O2 liberated by photosynthesis is made from
  the oxygen in water

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Photosynthesis is a redox process, as is cellular
respiration

• Water molecules are split apart and electrons and
  H ions are removed, leaving O2 gas
• These electrons and H ions are transferred to
  CO2, producing sugar

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Overview Photosynthesis occurs in two stages
linked by ATP and NADPH

• The complete process of photosynthesis consists
  of two linked sets of reactions
• the light reactions and the Calvin cycle
• The light reactions convert light energy to
  chemical energy and produce O2 (occurs in
  thylakoid membranes)
• The Calvin cycle assembles sugar molecules from
  CO2 using the energy-carrying products of the
  light reactions (occurs in stroma)

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An overview of photosynthesis
Chloroplast
CO2
Light
H2O
NADP
ADPP
LIGHTREACTIONS(in grana
CALVINCYCLE(in stroma
ATP
NADPH
O2
Sugar
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THE LIGHT REACTIONS CONVERTING SOLAR ENERGY TO
CHEMICAL ENERGY Visible radiation drives the
light reactions

• Certain wavelengths of visible light drive the
  light reactions of photosynthesis

X-rays
Micro-waves
Radio waves
Gammarays
UV
Infrared
Visible light
Wavelength (nm)
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Pigments

• Pigment a substance that absorbs light of a
  particular wavelength
• Wavelengths that are NOT absorbed are reflected
  (bounce off) or transmitted (pass through)
• So the material in which the pigment is found
  appears to be the color of the wavelengths that
  are NOT absorbed
• Photosynthetic pigments can absorb light energy
  make it available for conversion to chemical
  energy
• Chlorophyll a most common pigment in chloroplast
  (absorbs blue red light and reflects green light
  thus giving the chloroplast a green color)
• Accessory pigments

Reflectedlight
Light
Chloroplast
Absorbedlight
Transmittedlight
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Photons

• Light not only acts like waves, also made of
  particles called photons each carries a definite
  amount of energy depending on its wavelength
• Atoms can absorb light by capturing a photon
  energy of photon is transferred to an e- of the
  atom-gt bouncing it up to a higher energy level
• Green plants other photosynthetic autotrophs
  can store this energy in a chemical form-gt inside
  high energy compounds

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THE LIGHT REACTIONS CONVERTING SOLAR ENERGY TO
CHEMICAL ENERGY

• In the light reactions, electron transport chains
  generate ATP, NADPH, and O2
• Absorption of light energy by chlorophyll
  electrons excited
• as electrons drop back , energy released to
  do 3 things
• 1. split H20 molecule photolysis O2 given off
  as by-product
• 2. Hydrogen produced by splitting of water is
  attached to hydrogen carrier NADP -gt NADPH
• 3. energy from excited electrons used to
  make ATP
• (ADP P-gtATP)

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THE CALVIN CYCLE CONVERTING CO2 TO SUGARS

• ATP and NADPH power sugar synthesis in the Calvin
  cycle
• occurs in the chloroplasts stroma
• carbon fixation takes place and sugar is
  manufactured
• The Calvin cycle constructs G3P using
• carbon from atmospheric CO2
• electrons and H from NADPH
• energy from ATP
• Energy-rich sugar is then converted into glucose

INPUT
CALVINCYCLE
OUTPUT
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Review Photosynthesis uses light energy to make
food molecules
Cellular respiration
CALVIN CYCLE
LIGHT REACTIONS
CALVIN CYCLE
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Factors Affecting Rate of Photosynthesis

• Temperature increases rate up to a certain point
• Light Intensity increases rate up to a certain
  point
• CO2 level Increases rate up to a certain point
• Water decrease water, decrease photosynthesis
• Minerals Ex. Magnesium, Nitrogen

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Comparing Cellular Respiration Photosynthesis

• Cell Respiration

• Photosynthesis

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