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Photosynthesis, Chapter 6-1 page 111-116
• Capturing light energy and storing it within organic compounds
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Review
• What are…– Protons– Electrons– Compounds– photons– Organic – Inorganic– Carbohydrates– Glucose– ATP
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More review
• How are plant cells different from animal cells?
• What’s a chloroplast?
• What are different ways things get past cell membranes?
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Obtaining Energy
• Another way to classify living things• Autotrophs: obtain energy from light or
chemical reactions– They transduction of light chemical
energy
• Heterotrophs: organisms that get energy indirectly from eating autotrophs or other heterotrophs
• Remember: Auto = self, Hetero= other
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Energy Processes
• In photosynthesis, the products of one reaction gets consumed in the next reaction
• This series of reactions = biochemical pathway– Almost like many assembly lines connected
together
• Equation for photosynthesisCarbon Dioxide + Water -> Oxygen + Biomolecules
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Algae changes the world
• Early Earth had an atmosphere with no oxygen in it
• The only living things emitted oxygen as a waste product
• This changed the atmosphere
• Ironically, those species died
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We can’t let the plants get away with it
• The opposite of photosynthesis is cellular respiration
• Equation for cellular respirationBiomolecules + Oxygen -> Carbon Dioxide + Water
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chloroplasts
• Chloroplasts absorb light
• Flattened discs inside are called thylakoids
• Stacks of thylakoids = granum
• Fluid that all this is sitting in = stroma
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Lights, Chlorophyll, Action
• We see energy of different wavelengths as different kinds of color
• Pigments are compounds that absorb light
• If a color is absorbed it doesn’t reflect
• The color black absorbs most of the colors
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Pigments
• Chlorophyll is a pigment– It comes in two kinds a and b
• a absorbs more red light than b
• b only helps a so its an accessory pigment
• Green light is reflected from chlorophylls so plants appear green
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absorption spectra of photosynthetic pigments
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Other pigments
• Carotenoids absorb other colors and reflect earth tones
• You don’t normally see it until chlorophyll dies
• When does that happen during the year?
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Converting light energy
• Pigments capture light
• We’re going to store it in ATP & NADPH– Oxygen is a waste product of this reaction
• Pigments are clustered in photosystems
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Steps of photosynthesis1. Electrons get excited in photosystem II, and
they want to leave.2. Primary electron acceptor is sitting next to
photosystem II, waiting to take those electrons3. There’s a chain of molecules waiting to grab
these electrons. Together, they’re all called the electron transport chain.
• Energy from this is used to make a concentration gradient of H+
4. More light comes into another photosystem, photosystem I, another set of electrons start getting passed along
5. Finally energy from the electrons getting passed along is used to put a hydrogen on NADP+ making it NADPH
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Electron transport, simplified a little
All going on in a thylakoid1. Chlorophyll a molecules in Photosystem II get
excited from light2. e- are passed to the primary e- acceptor3. e- go down an electron transport chain4. These e- come into Photosystem I because
Photosystem I just gave away a pair5. Another electron transport chain combines
NADP+ with a Hydrogen atom to get NADPHNote where water gets split in all of this
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Chemiosmosis
• Part of the light reactions is the creation of ATP
• The energy for this comes from the concentration gradient of Hydrogen protons (H+)
• There are more H+ inside the cell than outside
• ATP Synthase lets H+ out and harnesses energy from that to make ATP
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Objectives, Now can you…
• Explain how the structure of a chloroplast relates to its function?
• Describe the role of chlorophylls and other pigments in photosynthesis?
• Summarize the main events of electron transport?
• Describe what happens to water in photosynthesis?
• Explain how ATP is synthesized during light reactions?