Chapter 10

• Plants – autotrophs (provide own food given certain circumstances)
• Need CO2, other inorganic (noncarbon based) materials obtained from environment.
• Autotrophs - producers of biosphere - provide food to rest of food chain.

• Green parts have chloroplasts leaves where most photosynthesis takes place.
• Green because of chlorophyll (green pigment inside of chloroplasts)
• Chlorophyll absorbs light energy to drive making of food in chloroplasts.

http://micro.magnet.fsu.edu/cells/chloroplasts/images/chloroplastsfigure1.jpg

• Chloroplasts found mostly in mesophyll (tissue in interior of leaf)
• CO
2 enters, O
2 leaves through stomata (microscopic pores in leaf)
• Leaves have veins - transfer water from roots to leaves.

*
• Within chloroplasts - dense fluid
(stroma)
• Thylakoid basic unit of photosynthesis.
• Each thylakoid stacked on top of each other (called a grana)
• Stroma fills in between grana.

• Formula for photosynthesis: 6H
2
O +
6CO
C
6
H
2
12
+ Light energy ---------->
O
6
+ 6O
2
• Water, carbon dioxide, and light combine to make glucose (sugar) and oxygen (waste)

http://static.howstuffworks.com/gif/irrigation-photosynthesis.gif

• Photosynthesis divided into 2 stages.
• 1 Light reactions (part controlled by light) and 2 Calvin cycle (also called dark reactions)

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/psoverview.gif

• Solar energy (sun) converted to chemical energy.
• Solar energy is in the form of waves, (electrochemical waves)
• Distance between peak of 2 electrochemical waves - wavelength.
• Wavelengths vary in distance from gamma rays to radio waves.

http://www.tortuga.com/science/Life%20is%20the%20Transformation%20of%20Solar%20Energy.jpg

• Entire range of radiation electromagnetic spectrum.
• Visible light provides us with color scheme.
• Light can be absorbed, reflected or transmitted when it meets matter.
• Pigments absorb light.

• All wavelengths absorbed - black.
• Chlorophyll a - pigment found in chloroplasts.
• Works best for blue and red light, least with green.
• Accessory pigments work with chlorophyll a to absorb light.

http://biology.clc.uc.edu/graphics/bio104/chlorophyll.jpg
Structure of chlorophyll

• One accessory pigments chlorophyll b (yellow colors)
• Chlorophyll b will transfer energy to chlorophyll a when it absorbs sunlight.
• Carotenoids dissipate light that may be harmful to chlorophyll a
(also found in human eye)

• Pigments absorb all wavelengths of visible light except green (why chloroplasts appear green; does not absorb this color, reflects it)
• Chlorophyll used by 2 systems in plant (photosystem I and photosystem II)

http://www.arborsci.com/CoolStuff/Chlorophyll.jpg

• Photons of light strike pigments electrons excited, transported through photosystems.
• Reaches specific chlorophyll molecule (reaction center) - light reactions begin.
• Photosystem I absorbs wavelength best at 700nm (dark red); photosystems II - 680nm (lighter red colors)

http://content.answers.com/main/content/wp/en/d/da/Photosystems.png

• When excited electrons reach reaction center, some electrons enter electron transport chain
(ETC) - generate energy (either reduced NADPH or ATP).
• 2 processes make that happen -
1
2 cyclic photophosphorylation; noncyclic photophosphorylation.

http://www.stanford.edu/group/hopes/treatmts/ebuffer/f_j13electtrans.jpg

• Occurs in photosystem I - make
ATP.
• ATP used to make glucose during dark reactions.
• Electrons in cyclic process move from reaction center through ETC, than back to reaction center.
• Does not make oxygen or NADPH.

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/cy clicphos.gif

• Starts in photosystem II.
• Electrons passed to reaction center.
• Then passed through ETC.
• Not returned to reaction center; sent to photosystem I.

Photosystems II Photosystem I http://www.und.ac.za/und/icd/citte/paper/net2/fig1a.gif

• They lose electrons (not recycled like in cyclic process) but get them from water.
• Produce oxygen as waste.
• Electrons sent to photosystem I used to make NADPH.

• As electrons make their way through ETCs, protons pumped out of stroma into thylakoid membranes.
• Creates proton gradient.
• Protons flow back into stroma and produce ATP.
• NADPH and ATP used in Calvin cycle (with CO2) to make sugars.

http://www.bioloj.ca/12U_Biology/img/12U_Biology/photosynthesis/Fig8_14b.jpg

• CO
2 fixed into carbohydrates using
ATP and NADPH from light reactions as energy.
• 1 st step - CO
2 fixed into 6 C sugar with 2 phosphate groups (ribulose biphosphate (or RuBP) )
• Done through enzyme - rubisco.

http://www.marietta.edu/~spilatrs/biol103/photolab/interMeta.gif

• RuBP 6 C compound - then split into
2 molecules (3-phosphoglycerate) which are both 3 C compounds.
• Each are phosphorylated by ATP, then reduced by NADPH - forms substance called G3P (form of sugar).

• For every 3 molecules of CO
2 molecules of G3P.
• At end - 6 molecules of G3P.
- 6
• 1 used by plant cell, other 5 recycled to regenerate RuBP to start process again.
• To make 1 G3P for plant, 9 molecules of ATP used, 6 molecules of NADPH used.

• Photosynthesis - C3 plants.
• 1 st product made is 3 C compound
(3-phosphoglycerate).
• Rice, wheat, and soybeans - C3 plants.
• Produce less food on hot, dry days
(stomata closed)
• No CO
2
- no Calvin cycle.

http://www.emeraldinsight.com/fig/0170950403003.png

• Instead of CO
2 adds O
2 being used, rubisco to Calvin cycle.
• No ATP generated no food produced.
• Called photorespiration.
• Wasteful product - not known why it still occurs in plants.

• C4 plants - alternate form of carbon fixation before Calvin cycle.
• Plants like sugarcane, corn, members of grass family.
• Have different anatomy.
• 2 different types of photosynthetic cells: bundle-sheath cells and mesophyll cells.

http://www.biology.lsu.edu/webfac/dlongstreth/biol12014f02/lectur37.jpg

• Bundle-sheath cells tightly packed and found around veins of leaf.
• Mesophyll cells found between bundle sheath and surface of leaf
(loosely packed).

http://gemini.oscs.montana.edu/~mlavin/b434/graphic/Leafc4m.jpg

• In bundle sheath cells, CO
2 produced as well as pyruvate.
• Pyruvate sent back to mesophyll cells; CO
2 used in bundle sheath cells to go into Calvin cycle.
• Then fixes CO
C3 plants.
2 with rubisco, like in
• C4 plants fix CO
2 twice.

• Plants live in hot, dry environments
(like corn and crab grass) where stomata have to close often.
• C3 plants - causes photorespiration;
C4 plants - still able to fix carbon.
• At cooler temperatures, C3 plants much more effective.

http://www.usep.edu.ph/smarrdec/Image%20Gallery%20Pics/corn%20laak.JPG

• CAM plants found in hot and dry environments where stomata are closed during the day.
• Plants open stomata at night, fix carbon during this time.
• Store products of carbon fixation for Calvin cycle which happens during the day.

• http://www.fw.vt.edu/dendro/forestbiology/ photosynthesis.swf