Photosynthesis

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Photosynthesis

• A naturally occurring biological process
• Very complex
• It is an endogenic, anabolic reaction resulting
  in the production of glucose and oxygen.
• Carried out by green plants, blue-algae and
  certain bacteria.

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• Organisms (autotrophs) are able to harness the
  energy contained in sunlight through a series of
  reactions.
• Resulting in the production of oxygen and sugar
  and other compounds.

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Overall equation for photosynthesis

• 6 CO2 6 H2O C6H12O6 6O2
• sunlight
• (radiant energy)
• Reactants Products

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Chloroplast

• Organelle where photosynthesis takes place
• Contain chemical compounds called Chlorophyll

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Leaf Structure

• Chloroplasts are concentrated in the mesophyll of
  the leaf
• Tiny pores in the lower epidermis (stomata)
  allows for CO2 to enter and O2 to exit.
• Veins carry water and nutrient from the plants
  roots to the leaves

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Chloroplast Structure

• Has inner and outer membranes
• Inner membrane encloses a thick fluid called
  STROMA
• Floating in the stroma are disk-shaped sacs
  called Thylakoids.(arranged in stacks called
  GRANA)

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Thylakoids

• The thylakoid is the structural unit of
  photosynthesis. Both photosynthetic prokaryotes
  and eukaryotes have these flattened sacs/vesicles
  containing chlorophyll

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The Light Reaction

• Take place in the thylakoid membranes, convert
  light energy to the chemical energy of ATP and
  NADPH.
• The light reactions use the reactant water from
  the equation and release the product oxygen.

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Calvin Cycle

• Like a sugar factory within a chloroplast.
• It is called a cycle because the starting
  material is regenerated each time the process
  occurs.
• The starting material that gets regenerated is a
  compound called RuBP, a sugar with five carbons

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The Calvin cycle

• Takes place in the stroma
• Uses ATP and NADPH to convert carbon dioxide to
  sugar

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Inputs and Outputs(Reactant and Products)

• With each turn of the Calvin cycle, there are
  chemical inputs and outputs.
• The inputs are carbon dioxide from the air and
  the ATP and NADPH produced by the light
  reactions.

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Calvin Cycle Inputs

• The Calvin cycle uses carbon from the carbon
  dioxide, energy from the ATP, and high-energy
  electrons and hydrogen ions from the NADPH.

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Calvin Cycle Outputs

• Is an energy-rich sugar molecule. That sugar is
  not yet glucose, but a smaller sugar named G3P.
• The plant cell uses G3P as the raw material to
  make glucose and other organic molecules it
  needs.

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Summary of Photosynthesis

• Recall that the overall equation for
  photosynthesis is
• 6 CO2 6 H2O C6H12O6 6 O2

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Flow of Energy

• By converting light energy to chemical energy,
  photosynthesis is the first step in the flow of
  energy through an ecosystem.

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Some of that chemical energy then passes from
producers to consumers. Even when people eat
meat, you can trace its stored energy back to
photosynthesis. Photosynthesis is the ultimate
source of all the food you eat and all the oxygen
you breathe.
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• The nature of light
• The energy produced by the sun reaches the earth
  as electromagnetic radiation.
• Light and other forms of electromagnetic
  radiation are considered to have both a wave
  nature and a particle nature.

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• Particles or packets of light (its particle
  nature) are known as photons - the smallest
  divisible units of light.
• The distance moved by a photon during one of it
  vibrations is referred to as its wavelength and
  is measured in nanometers (nm).

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Visible light

• A very small part of this spectrum can be seen by
  the human eye i.e. between the wavelengths 400
  and 700 nm.
• This part of the electromagnetic spectrum is
  called visible light.
• Almost all life depends ultimately on this part
  of the spectrum for its energy.

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Why plants only use visible light as a source of
energy for photosynthesis

• Visible light
• Each photon of visible light contains just enough
  energy to excite the electrons of molecules
  without causing damage to the cell.

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Light and photosynthesis

• Chlorophyll absorbs blue-violet and red-orange
• Reflects green back
• Chlorophyll a, the most important light-absorbing
  pigment in plants, does not absorb light in the
  green part of the spectrum.  Light in this range
  of wavelengths is reflected.

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Light and photosynthesis

• Plants do not depend only on chlorophyll a but
  also have other pigments (accessory pigments)
  which absorb light of  different wavelengths.