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 to determine where the mass came from.
  
• He concluded that the mass grew from the water,
  because that was the only thing he had added to
  the pot. Later it was determined that most of the
  mass comes from the air.

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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. Some bacteria and protists are also
  autotrophs.
• Photosynthesis and chemosynthesis are two ways in
  which organisms can make food.

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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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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?