Photosynthesis

Getting Energy Autotrophs- make their own energy (usually from the sun) Ex. plants Heterotrophs- get energy from other organisms Ex. animals, funguses

Photosynthesis Photosynthesis- using energy from the sun to create glucose. Plants use glucose to make ATP and Sugars Reactants- Carbon Dioxide, Sunlight, Water Products – Oxygen Glucose Sun + 6 CO H 2 O C 6 H 12 O O 2

Reactants: Fig CO 2 Products: 12 H 2 O 6 O 2 6 H 2 O C 6 H 12 O 6

Chloroplasts Found in the mesophyll (interior tissue) of leafs Thylakoids -(located inside chloroplasts) help capture sunlight for plants. They are arranged in stacks called grana. Stroma - region of fluid filled space outside the thylakoids Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Chlorophyll Chlorophyll – the pigment in chloroplasts. Pigments are substances that absorb visible light (different pigments absorb different light) Chlorophyll transmitts green light, absorbs all others.**** There are other pigments such as Chlorophyll B and carotenoids present in plants.

Spectrophotometer - measures a pigment’s ability to absorb various wavelengths of light sends light through pigments and measures amount of light transmitted Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Spectrophotometer

absorption spectrum - is a graph plotting a pigment’s light absorption versus wavelength The absorption spectrum of chlorophyll suggests that violet-blue and red light work best for photosynthesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Absorption Spectrum

Action Spectrum action spectrum – tells you which wavelength of light actually drives photosynthesis the best. Engelmann made an action spectrum using algae and bacteria. (the more 0 2 the algae released, the more the bacteria grew)

What’s light got to do with it? Chloroplasts use light photons to help take electrons from water. The electrons are then added to CO 2 to make glucose. (A Redox Reaction) Sun + 6 CO H 2 O C 6 H 12 O O 2 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings e-

Reduction/Oxidation (Redox) Reaction Reduction – to gain electrons Oxidation – to loose electrons. Photosynthesis is a redox process in which H 2 O is oxidized and CO 2 is reduced OIL RIG or LEO GER Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Light Reaction (the “photo” part) Light reaction requires sunlight –In thylakoid –Happens in the light –Water is oxidized –Produces NADPH & ATP

Photosystem The thylakoid membranes contain photosystems photosystem – pigment molecules attached to proteins (light harvesting complex) that funnels light energy into a reaction center where electrons are transferred. Light comes in electrons come out. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Photosystem II (PII) Light first enters photosystem II (discovered 2 nd ) The light excites chlorophyll molecules, who excited other chlorophyll molecules by passing on photons.

Splitting Water Meanwhile, water is split into Hydrogen and Oxygen by enzymes. (so don’t forget to water your plants!) The Oxygen is released as waste (good for us) The Hydrogen is kept

P680 P680 (likes 680nm light) – a special chlorophyll molecule in photosystem II that takes electrons from the hydrogen that came from the split water. (it really likes electrons) The water has been oxidized

Primary Electron Acceptor Remember the photons being passed by the chlorophyll? They get sent to P680. P680 gets so exited that it loses the electrons it received from water. Primary Electron Acceptor – a molecule in the reaction center that receives electrons from P680.

Electron Transport Chain Linear Flow - The primary electron acceptor sends the electrons down the electron transport chain to Photosystem I (discovered 1 st ). On the way down, movement of the electrons is used to make ATP.

ATP Production As electrons move, they cause the Hydrogens (protons) from water to move out of the membrane into the thylakoid space. As hydrogens build up in the thylakoid space they are forced back through the membrane through ATP synthase into the stroma.

ATP Synthase ATP synthase – enzyme that makes ATP as hydrogens pass through.

Photosystem I (PI) Meanwhile the electrons from the ETC have reached photosystem I. (similar to photosystem II) P700 in photosystem I is going to receive electrons coming from the ETC. (the electrons are not coming from water this time.)

Photosystem I cont’d Light excites chlorophyll molecules in PI who excite other chlorophyll molecules by passing on photons. The photons get sent to P700 who gets so excited that it loses the electrons it got from the ETC.

Cyclic Flow The primary electron acceptor receives the electrons from P700. The primary acceptor can then send the electrons back to the top of the ETC so they call come down again and make more ATP. This is cyclic flow.

NADPH The primary acceptor in PI can also send the electrons to an electron carrier called NADP+. Once NADP+ gets electrons to carry (gets reduced) it becomes NADPH.

Moving On The NADPH will take electrons to the stroma to begin the second cycle. ATP will also go to the stroma to help.****

Calvin Cycle (the “synthesis” part) Calvin cycle ~ AKA Light-Independent reaction –In stroma –Happens in both light & dark –CO 2 is Reduced –Uses ATP and NADPH from Light Reaction –Produces Glucose

Carbon fixation- Incorporating Carbon dioxide A 5 carbon sugar named RuBP awaits CO 2 An enzyme named rubisco adds one CO 2 to RuBP to make a 6 carbon sugar. (this happens three times) The 6 carbon sugar then splits into two 3 carbon molecules phase 1 Carbon Fixation

phase 2 Reduction Reduction – adding electrons ATP is used to add a phosphate to the 3 carbon molecules (makes the molecule unstable) NADPH then reduces the 3 carbon molecule, replacing the newly added phosphate with electrons. 3 carbon molecule is now called G3P.

phase 3 Regeneration Regeneration – replacing RuBP 1 Molecule of G3P is sent out to make glucose (2 G3P’s make 1 glucose) 5 Molecules of G3P are used to make RuBP (remember this all happens 3 times)****

Fig. 10-UN2 Regeneration of CO 2 acceptor 1 G3P (3C) Reduction Carbon fixation 3 CO 2 Calvin Cycle 6  3C 5  3C 3  5C

Fig. 10-UN4

C 3 Plants C 3 Plants – (most plants)initial fixation of CO 2, via rubisco, forms a three-carbon compound On hot, dry days, plants close stomata, which conserves H 2 O but also limits intake of CO 2 So some plants use strategies besides C 3.

C 4 Plants C 4 plants –counteract hot dry days by fixing CO 2 into four-carbon compounds in mesophyll cells. It requires the enzyme PEP carboxylase because it can fix CO 2 even when there isn’t much of it.

C 4 Cont’d The four-carbon compounds are send to bundle- sheath cells, where they release CO 2 that is then used in the Calvin cycle. Increases CO 2 for the calvin cycle when stomata are closed to save water.

CAM Plants Cam plants use CAM to fix CO 2 into 4 carbon molecules. To do this, CAM plants open their stomata at night Stomata close during the day, and CO 2 is released from the 4 carbon molecules and used in the Calvin cycle

You should now be able to: 1.Describe the structure of a chloroplast 2.Describe the relationship between an action spectrum and an absorption spectrum 3.Trace the movement of electrons in linear electron flow 4.Trace the movement of electrons in cyclic electron flow Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

5.Describe the role of ATP and NADPH in the Calvin cycle 6.Describe two important photosynthetic adaptations that cope with hot dry conditions. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings