Photosynthesis, Chapter 6-1 page 111-116

• Capturing light energy and storing it within organic compounds

+

Review

• What are…– Protons– Electrons– Compounds– photons– Organic – Inorganic– Carbohydrates– Glucose– ATP

More review

• How are plant cells different from animal cells?

• What’s a chloroplast?

• What are different ways things get past cell membranes?

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

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

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

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

chloroplasts

• Chloroplasts absorb light

• Flattened discs inside are called thylakoids

• Stacks of thylakoids = granum

• Fluid that all this is sitting in = stroma

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

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

absorption spectra of photosynthetic pigments

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?

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

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

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

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

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?