Photosynthesis

• is the process that converts solar energy into chemical energy

  Photosynthesis
• sustain themselves without eating anything derived from other organisms

  Autotrophs
• Autotrophs are the ____ of the biosphere, producing organic molecules from CO2 and other inorganic molecules

  producers
• Almost all plants are ___ , using the energy of sunlight to make organic molecules from H2O and CO2

  photoautotrophs
• obtain their organic material from other organisms

  Heterotrophs
• are the consumers of the biosphere

  Heterotrophs
• Photosynthesis converts light energy to the chemical energy of food
• are structurally similar to and likely evolved from photosynthetic bacteria • The structural organization of these cells allows for the chemical reactions of photosynthesis

  Chloroplasts
• The Sites of Photosynthesis in Plants

  Chloroplasts
• (organ) are the major locations of photosynthesis

  Leaves
• (leaves)Their green color is from ___, the green pigment within chloroplasts

  chlorophyll
• Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast
• CO2 enters and O2 exits the leaf through microscopic pores called 


  stomata
• Chloroplasts are found mainly in cells of the ___, the interior tissue of the leaf

  mesophyll
• A typical mesophyll cell has __ - __ chloroplasts
• The chlorophyll is in the membranes of ____(connected sacs in the chloroplast); thylakoids may be stacked in columns called grana (granum)

  thylakoids
• Chloroplasts also contain , a dense fluid


  stroma
• Photosynthesis can be summarized as the following equation: Light energy -> Glucose -> Water

  or

  6 CO2 + 12 H2O + Light energy ® C6H12O6 + 6 O2 + 6 H2O
• Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules
• Photosynthesis as a Redox Process

  Photosynthesis is a redox process in which H2O is oxidized and CO2 is reduced

  
• The Two Stages of Photosynthesis

  light reactions and Calvin cycle
• the photo part of photosynthesis

  light reactions
• the synthesis part of Photosynthesis

  Calvin cycle
• • The light reactions (in the thylakoids):

  • Split H2O

  • Release O2

  • Reduce NADP+ to NADPH

  • Generate ATP from ADP by photophosphorylation

  • The Calvin cycle (in the stroma) forms sugar from CO2, using ATP and NADPH

  • The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules
• The light reactions convert solar energy to the chemical energy of ATP and NADPH
• The Nature of Sunlight: Light is a form of energy known as electromagnetic energy, also called electromagnetic radiation.
• Wavelength - the distance between the crests of electromagnetic waves.
• • Electromagnetic spectrum - entire range of radiation
• The segment most important to life is the narrow band from about 380 nm to 750 nm in wavelength (visible light).

  • Behave as a photon (particle).
• The amount of energy is inversely related to the wavelength of the light.

  
• Substances that absorb visible light are known as pigments.
• WHY DO LEAVES ARE GREEN?

  Chlorophyll
• Chlorophyll molecules of chloroplast absorb blue- violet and red light and reflect or transmit green light.
• Spectrophotometer – an instrument which measures the ability of a pigment to absorb various wavelengths of light. --- Absorption spectrum
• 3 Types of Pigments in a Chloroplast|

  1. 1. chlorophyll a - which participates directly in the light reactions • Absorbs light • Can be found in all photosynthetic plants, algae and cyanobacteria.
  2. chlorophyll b - the accessory pigment • Absorbs light • Can be found in plants and green algae
  3. Carotenoids – group of accessory pigment • Absorb violet and blue-green light • Absorb excess energy and dissipate it as heat

  
• Carotenoids • absorb and dissipate excessive light energy that would otherwise damage chlorophyll or interact with oxygen, forming reactive oxidative molecules that are dangerous to the cell.
• What exactly happens when chlorophyll and other pigments absorb light? Excitation
• Photosystem • composed of a reaction- center complex surrounded by several light-harvesting complexes
• Reaction-center complex – chlorophyll a

  Light-harvesting complex- various pigments bounds to proteins
• primary electron acceptor - a molecule capable of accepting electrons and becoming reduced.