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What is ATP?. Adenosine Tri-phosphate. Base. Phosphate Groups. Sugar. ATP. Exergonic. Endergonic. ADP. Catabolic and Anabolic Pathways depend on ATP / ADP shuttle. Figure 10.0 Sunbeams. Photosynthesis. Photoautotrophs. Question:. Where does photosynthesis take place?. - PowerPoint PPT Presentation
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Catabolic and
Anabolic Pathways depend on ATP / ADP
shuttle
Figure 10.0 Sunbeams
Question:•Where does photosynthesis take place?
http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/harvestinglight.swf
Plants• Autotrophs: self-producers.• Location:
1. Leaves
a. stoma
b. mesophyll cells
StomaMesophyllCell
Chloroplast
Stomata (stoma)• Pores in a plant’s cuticle through which water
and gases are exchanged between the plant and the atmosphere.
Guard Cell
Guard Cell
Carbon Dioxide (CO2)
Oxygen (O2)
Mesophyll Cell
Cell Wall
Nucleus
Chloroplast
Central Vacuole
Chloroplast
• Organelle where photosynthesis takes place.
GranumThylakoid
Stroma
Outer Membrane
Inner Membrane
Thylakoid
Thylakoid Membrane
Thylakoid SpaceGranum
Chloroplast• Chlorophyll – green pigment located
inside chloroplasts• Found in mesophyll (interior of leaf)• Double membrane• Enclose stroma (dense liquid)
containing grana made up of thylakoid membranes which contain chlorophyll
PhotosynthesisH2O CO2
O2 C6H12O6
Light Reaction
Dark Reaction
Light is AdsorbedBy
Chlorophyll
Which splitswater
Chloroplast
ATP andNADPH2
ADPNADP
Calvin Cycle
Energy
Used Energy and is recycled.
+
+
Photosynthesis
• An anabolic, endergonic, carbon dioxide (CO2) requiring process that uses light energy (photons) and water (H2O) to produce organic macromolecules (glucose).
6CO2 + 6H2O C6H12O6 + 6O2
glucose
SUN
photons
Question:•Why are plants green?
Chlorophyll Molecules• Located in the thylakoid membranes.
• Chlorophyll have Mg+ in the center.
• Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red-660 nm are most important).
• Plants are green because the green wavelength is reflected, not absorbed.
Light Absorption Spectrum
Absorption of Chlorophyll
wavelength
Absorption
violet blue green yellow orange red
Question:•During the fall, what causes the leaves to change colors?
Fall Colors• In addition to the chlorophyll pigments, there
are other accessory pigments present.
• During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments.
• Carotenoids are pigments that are either red or yellow.
Chromatography• Pigments can be separated out using the
process of CHROMATOGRAPHY.
Redox Reaction• The transfer of one or more electrons from
one reactant to another.
• Two types:
1. Oxidation
2. Reduction
Oxidation Reaction• The loss of electrons from a substance.• Or the gain of oxygen.
glucose
6CO2 + 6H2O C6H12O6 + 6O2
Oxidation
Reduction Reaction• The gain of electrons to a substance.• Or the loss of oxygen.
glucose
6CO2 + 6H2O C6H12O6 + 6O2
Reduction
Breakdown of Photosynthesis
• Two main parts (reactions).
1. Light Reaction or
Light Dependent Reaction
Produces energy from solar power (photons) in the form of ATP and NADPH.
Breakdown of Photosynthesis
2. Calvin Cycle or
Light Independent Reaction or
Carbon Fixation or
C3 Fixation
Uses energy (ATP and NADPH) from light rxn to make sugar (glucose).
Chlorophyll• Two different types : Chlorophyll a and b• “a” – main pigment in photosynthesis• “b” – accessory pigment
– Both have similar structure but absorb different wavelengths of light
• Chlorophyll absorbs light of a particular wavelength, electrons are excited and jump to higher energy level, drops back down and gives off heat
• This energy is passed along until it finds Chlorophyll a, which, when excited, passes electron to primary electron acceptor…powering light dependent reactions.
How a photosystem harvests light..
1. Light Dependent Reaction
• Occurs in the Thylakoid membranes
• During the light reaction, there are two possible routes for electron flow.
A. Photosystem II
B. Photosystem I
*Pigments of the thylakoid space organize themselves into groups called photosystems
Chemiosmosis• Powers ATP synthesis.
• Located in the thylakoid membranes.
• Uses ETC and ATP synthase (enzyme) to make ATP.
• Photophosphorylation: addition of phosphate to ADP to make ATP.
Chemiosmosis…Making ATPH+ H+
ATP Synthase
H+ H+ H+ H+
H+ H+high H+
concentration
H+ADP + P ATP
PS II PS IE
TC
low H+
concentration
H+ThylakoidSpace
Thylakoid
SUN (Proton Pumping)
Things to Remember….
Light Reactions…• Occur in the Thylakoid Membrane• Inputs are water and light• Products : ATP, NADPH and O2
• Oxygen produced comes from the water, not Carbon Dioxide!
• Two different pathways…..
Cyclic vs. Noncyclic Pathways…
• Noncyclic Light Reaction– Electrons taken from Chlorophyll a are not
recycled back down to the ground state – therefore do not make it back to the chlorophyll molecule when the reaction is complete. Electrons end up on NADPH
• Cyclic Light Reaction– Uses ONLY Photosystem I, sunlight hits P700– Energy given off down ETC, only produces
ATP
…Because of the Calvin Cycle
• Calvin Cycle uses more ATP than NADPH• This is eventually a problem because the
Light Reaction produces equal amounts of ATP and NADPH
• Plants compensate for this disparity by dropping into the cyclic phase when ATP is needed to keep the Light Independent Reaction from coming to a grinding halt!!!
Calvin Cycle
GranumThylakoid
Stroma
Outer Membrane
Inner Membrane
Light-Independent Reaction takes place in Stroma
Begins Synthesis Phase of Photosynthesis
Chloroplast
Meet Mr. Melvin Calvin
Calvin Cycle• The light reactions provide ATP and
NADPH for the Calvin cycle• Process of carbon fixation – CO2 from air
incorporated into organic molecules• Fixed carbon reduced to form a
carbohydrate (powered by NADPH electrons and energy from ATP)
• Enzyme “Rubisco” assists in reduction• Product is actually glyceraldehyde-3-
phosphate (G3P or GAP) – a 3-carbon molecule
Calvin Cycle• For 1 molecule of GAP, the cycle must take
place 3 times• GAP can be used to make carbohydrates
(like glucose), amino acids, lipids, nucleic acids, and other needed molecules.
• The Calvin cycle begins and ends with ribulose-1,5-biphosphate (RuBP)
• At the end of the cycle, 3 CO2 molecules have formed 6 GAP molecules.
• One GAP molecule is used by the plant cell, the other 5 are used to regenerate RuBP
Calvin Cycle
Things to remember about Calvin Cycle (C3 Fixation)…
• Occurs in Stroma of Chloroplast• Inputs: NADPH, ATP and CO2
• Products: NADP+, ADP and a sugar.• More ATP used than NADPH = need for
Cyclic Photophosphorylation• Carbon of sugar comes from CO2
• To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.
• Some plants must make changes to the system in order to successfully use light to produce energy.
• Transpiration = water loss
• Stomata can be closed to prevent water loss, however they experience a shortage of CO2 and the O2 produced in photosynthesis is unable to leave plant.
Guard Cell
Guard Cell
Photorespiration• Occurs on hot, dry, bright days.
• Stomates close.
• Fixation of O2 instead of CO2.
• Produces 2-C molecules instead of 3-C sugar molecules.
• Produces no sugar molecules or no ATP.• Result = plants have lowered capacity for
growth
Photorespiration
• Because of photorespiration: Plants have special adaptations to limit the effect of photorespiration.
1. C4 plants
2. CAM plants
C3 Plants• Examples: rice, wheat, bluegrass, and
soybeans• The cyclic series of reactions whereby CO2
is fixed into a 3-carbon carbohydrate during the Calvin cycle.
• During hot, dry days, these plants must keep their stomata closed to prevent water loss.
• O2 build up and CO2 cannot be replenished.• Uses photorespiration to convert O2 to CO2.
• Produces no ATP nor food – actually decreases photosynthetic output.
C4 Plants• Examples: tropical and desert plants, as well
as sugar cane, and corn. (15% of plants)• The series of reactions that efficiently fixes CO2
into 4- carbon organic acids for later release and incorporation into the C3 (Calvin) cycle.
• The 4-carbon molecule (oxaloacetate) can easily regenerate CO2 that reenters the Calvin cycle.
• The reaction requires lots of ATP and is only advantageous when lots of light and little water are available.
C4 Plants vs. C3 Plants• Has 2 different types of photosynthetic
cells: Mesophyll Cells and Bundle Sheath Cells
• Divides photosynthesis spatially.
–Light rxn - mesophyll cells.–Calvin cycle - bundle sheath cells.
• C4 uses PEP Carboxylase to drive photosynthesis by fixing carbon.
C4 Leaf Anatomy and the C4 Pathway
CAM Plants• Examples: succulents including many cacti and
pineapples that live in very arid climates (5%)• Open stomata at night and close them during the
day.• The mesophyll cells of CAM plants store the CO2 (at
night) in the form of acids until needed the next day.• During the day when stomata are closed, CO2 is
released from the organic acids and enters the Calvin cycle.
• This must occur during the day instead of night because the light reactions must supply ATP and NADPH for the Calvin cycle.
C4 vs. CAM Plants
A Review of Photosynthesis