Photosynthesis

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Photosynthesis

• STEP Grade 9

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Simple Diagram of a Leaf
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Cross Section of a Leaf
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The Chloroplast
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The Chloroplast

• Stroma  The matrix surrounding the grana in the
  inner membrane of chloroplasts. The area between
  membranes (thylakoids, grana) inside the
  chloroplast.
• Grana A series of stacked thylakoid disks
  containing chlorophyll found in the inner
  membrane of chloroplasts.

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Chlorophyll
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Reactions of Photosynthesis

• 6CO2 6H2O C6H6O6 6O2
• The process is a lot more complex
• Actually takes place in two separate stages
• The Light reactions occurs in grana
• The Dark reactions occurs in stroma

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The Light Reactions

• The purpose of the light reactions is to change
  light energy into chemical energy in the form of
  2 chemicals ATP and NADPH.
• Requires light
• Light energy used to make ATP.
• The light splits water into hydrogen ions (H)
  and oxygen atoms.
• The oxygen is released to the air.
• The H ions are used to make NADPH
• ATP carries energy to the dark reactions.
• NADPH carries energy and H to the dark reactions.

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The Dark Reactions

• The purpose of the dark reactions is to change
  CO2 into sugar by adding energy the H ions
  from ATP NADPH.
• Can occur in light or dark.
• 6 CO2 lots of ATP NADPH are needed to make
  one sugar molecule.
• The sugar is then used for plant growth or stored
  for use in fruits and leaves of plants as food
  for animals

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Light Dark Reactions
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Limiting Factors

• Factors affecting the rate of photosynthesis.
• As the rate of photosynthesis increases so will
  the plants growth rate.
• Three factors limit photosynthesis from going any
  faster Light level, carbon dioxide level, and
  temperature.
• Without enough light a plant cannot
  photosynthesize very fast, even if there is
  plenty of water and carbon dioxide. Increasing
  the light intensity will make photosynthesis
  faster.

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Limiting Factors

• Sometimes photosynthesis is limited by the level
  of carbon dioxide. Even if there is plenty of
  light a plant cannot photosynthesize if it has
  run out of carbon dioxide.
• Temperature can be a limiting factor too. If it
  gets too cold the rate of photosynthesis will
  slow right down equally, plants cease to be able
  to photosynthesize if it gets

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Limiting Factors
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Questions

1. Which graph best shows the effect of increasing
   light intensity on the rate of photosynthesis?
2. Which graph best shows the effect of increasing
   carbon dioxide concentration on the rate of
   photosynthesis? A
3. Which graph best shows the effect of increasing
   temperature if light and carbon dioxide are not
   limiting (i.e. the levels of light and carbon
   dioxide are high). A