Photosynthesis

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Photosynthesis
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Photosynthesis
Where does the energy come from that sustains all
life?
The Sun!!
Well most of it anyway
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What is photosynthesis?

• In the process of photosynthesis, plants convert
  the energy of sunlight into the energy in the
  chemical bonds of carbohydrates-sugars and
  starches.

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Discovery of the process

• For many years, people wondered how a few
  seedlings could develop into a large tree.
• The mass of seedlings are only a few grams, where
  as the mass of a tree is several tons.
• Dutch physician Jan Van Helmont devised an
  experiment.
• He concluded that the mass grew from the water,
  because that was the only thing he had added to
  the pot.
• This was just one of the things needed for
  photosynthesis to occur.

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What makes photosynthesis complete?

• Helmont did not realize that carbon dioxide in
  the air also plays a major role in the
  contribution of mass growth.
• The carbon in carbon dioxide is what is used to
  make carbohydrates in photosynthesis.

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• Later on, scientist Joseph Priestly performed an
  experiment that would give rise to why oxygen is
  released in photosynthesis, and why sunlight is
  needed for it to photosynthesize.
• Priestly placed a candle in a jar along with a
  mint plant.
• He then realized that the candle could only stay
  lit when the mint plan was present.
• This would mean that the plant was releasing
  oxygen.

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Why is Photosynthesis important?

• Through experiments, it was realized that in the
  presence of light, plants transform carbon
  dioxide and water into carbohydrates and release
  oxygen.
• Plants that are able to use a source of energy,
  such as sunlight, to provide food directly from
  simple inorganic molecules are known as
  autotrophs.
• This is made possible through photosynthesis.

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Quick Concept Check

• WHAT IS THE DIFFERENCE BETWEEN A HETEROTROPH AN
  AUTOTROPH?

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the equation for photosynthesis is
LIGHT
Carbon Dioxide
Glucose

Oxygen

Water
LIGHT
6 CO2
6 H2O

C6 H12 O6
6O2

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The sugars that result from photosynthesis are
produced by adding the hydrogen ions and
electrons from water to carbon dioxide, NOT by
splitting CO2 and adding water!
oxidized
H and e-
6CO2 12H2O ? C6H12O6 6O2 6H2O
reduced
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Quick Concept Review INDICATORS!

• Bromothymol Blue
• Used to test for the presence of carbon dioxide
  (CO2)
• If CO2 is present it is a yellow color
• If CO2 is NOT present it is a blue color

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Light Absorption Light Energy

• The actual process of photosynthesis begins when
  light is absorbed by pigments in the plant cell.
  
• The principal pigment in plants is chlorophyll
  which gives the plant its green color.

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Plant Photosynthesis
internal leaf structure
chloroplasts
outer membrane
inner membrane
thylakoid
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Photosystems use some wavelengths of light but
reflect others
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• Another way in which light energy is trapped in
  chemical form involves adenosine triphosphate or
  ATP.
• During photosynthesis, green plants produce ATP,
  which is the energy storing compound used by
  every living cell.
• The energy is released by means of breaking the
  phosphate bonds which make up the ATP cycle.
• The energy is used in almost all cellular
  activities.

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Respiration vs. Photosynthesis
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• Photosynthesis and respiration are complementary
  processes in the living world.
• Photosynthesis uses the energy of sunlight to
  produce sugars and other organic molecules.
• These molecules in turn serve as food.
• Respiration is a process that uses O2 and forms
  CO2 from the same carbon atoms that had been
  taken up as CO2 and converted into sugars by
  photosynthesis.
• In respiration, organisms obtain the energy that
  they need to survive.
• Photosynthesis preceded respiration on the earth
  for probably billions of years before enough O2
  was released to create an atmosphere rich in
  oxygen.
• (The earth's atmosphere presently contains 20
  O2.)

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Self-Evaluation Questions

• 1. In the process of photosynthesis, plants
  convert the energy of sunlight into what?
• 2. When Helmont devised an experiment, he
  concluded that the mass grew from the_____, which
  was the only thing he had added to the soil.
• 3. What scientist gave rise to the explanation
  of plants giving off oxygen, and the reason
  sunlight is needed in order for plants to
  photosynthesize?
• 4. Fill in the missing part of the equation for
  photosynthesis--Carbon dioxide water yields
  what? (two things)
• 5. What do you call plants that obtain their
  nutrients in organic molecules through
  photosynthesis?