Transcript Photosynthesis

Photosynthesis
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.
Structure
• 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)
• CO2 enters, O2 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: 6H2O +
6CO2 + Light energy ---------->
C6H12O6+ 6O2
• 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.
• 1Light reactions (part controlled by
light) and 2Calvin 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.
• 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)
Light reactions
• 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 1cyclic photophosphorylation;
2noncyclic photophosphorylation.
http://www.stanford.edu/group/hopes/treatmts/ebuffer/f_j13electtrans.jpg
Cyclic photophosphorylation
• 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
Noncyclic
photophosphorylation
• 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
The Calvin cycle
• CO2 fixed into carbohydrates using
ATP and NADPH from light
reactions as energy.
• 1st step - CO2 fixed into 5 C sugar
with 2 phosphate groups (ribulose
biphosphate (or RuBP) )
• Done through enzyme - rubisco.
• So, RuBP 5 C compound adds one
CO2 to make a 6 C
• Then split into 2 molecules (3phosphoglycerate) which are both 3
C compounds.
• 2nd step - Each are phosphorylated
by ATP, then reduced by NADPH forms substance called G3P (form
of sugar).
• 3rd step- regenerate 5 C RuBP the
CO2 acceptor.
• For every 3 molecules of CO2 - 6
molecules of G3P.
• At end - 6 molecules of G3P.
• 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.
Alternate forms of
photosynthesis
• Photosynthesis - C3 plants.
• 1st product made is 3 C compound
(3-phosphoglycerate).
• Rice, wheat, and soybeans - C3
plants.
• Produce less food on hot, dry days
(stomata closed)
• No CO2 - no Calvin cycle.
http://www.emeraldinsight.com/fig/0170950403003.png
• Instead of CO2 being used, rubisco
adds O2 to Calvin cycle.
• No ATP generated no food
produced.
• Called photorespiration.
• Wasteful product - not known why
it still occurs in plants.
C4 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, CO2
produced as well as pyruvate.
• Pyruvate sent back to mesophyll
cells; CO2 used in bundle sheath
cells to go into Calvin cycle.
• Then fixes CO2 with rubisco, like in
C3 plants.
• C4 plants fix CO2 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
• 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