photosynthesis
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Photosynthesis. Bio I Rupp. Focusing Questions. Where does the energy to do work come from? What chemical do cells use for energy? What is the equation for photosynthesis? How are chloroplasts arranged? What is NADPH? What are the two reaction pathways in photosynthesis?. Energy. - PowerPoint PPT PresentationTRANSCRIPT
Bio IRupp
Focusing QuestionsWhere does the energy to do work come
from?What chemical do cells use for energy?What is the equation for photosynthesis?How are chloroplasts arranged?What is NADPH?What are the two reaction pathways in
photosynthesis?
EnergyLight or solar
energy is converted to chemical energy
This occurs in the chloroplast of plants
PlantsBlue-green algaePhotosynthetic
bacteria
History of PhotosynthesisJan van HelmontBelgian Physician1643Willow tree
experimentWhat caused the
tree to gain weight?
History of Photosynthesis con’t.Joseph PriestleyEnglish minister and chemist1771Candle experimentWhat did the plant produce?
History of Photosynthesis con’t.Jan IngenhouszDutch scientist1779Repeat of Priestley’s workPlants only functioned in what?
History of Photosynthesis con’t.Based on the experiments of van Helmont,
Priestley, and Ingenhousz, what three things can we say plants need/produce?
Photosynthesis EquationCO2 + H2O + Light C6H12O6 + O2
Leaf StructureEpidermis—outer cells of leafPalisade mesophyll—where the majority of
chloroplasts are locatedSpongy mesophyll—some chloroplasts are
located here
Leaf Structure con’t.Xylem—water transportPhloem—food transportCuticle—waxy covering that stops
evaporation of water from the leavesStoma—opening in leaf that allows CO2 to
enter
Chloroplast structureStroma—the fluid interior that surrounds the
other chloroplast structuresGranum—stacks of disk shaped thylakoidsThylakoids—the site of photosynthesis
Chloroplast structure con’t.What makes the chloroplasts green?Pigments
Chlorophyll a (650-700nm and 400-450nm)Chlorophyll b (450-500nm and 650nm)Carotenoids (450 nm)Xanthophyll (600nm)
How does Photosynthesis Work?Light is capturedLight energy is converted to chemical energyThe chemical energy is a combination of
ATPNADPHSugars
Light reaction pathwaysDark reaction pathways
Light ReactionsStep one
Light hits photosystem II and boosts electrons to higher energy level
H+ ions are transported to create a concentration gradient
ATP is produced
Light Reactions con’t.Step Two
Low energy electrons enter photosystem I and is re-energized
The re-energized electrons then move into the NADPH electron chain
Restoring Photosystem IIIf electrons keep
moving out where are the initial electrons coming from?
Water splitting reaction
H+ ions and ATP CreationHow did H+ ions
move across the thylakoid membrane?
They were pumped by ATP synthase
Facilitated diffusion
Dark ReactionsAlso known as the Calvin Cycle or Light
Independent reactionsThe ATP and NADPH from the light reactions
is used to turn CO2 into sugar
Dark Reactions con’t.Step one
Carbon fixationCO2 is attached to a
5 carbon sugar called ribulose bisphosphate (RuBP)
The resultant molecule is unstable and splits into two 3-carbon molecules of PGA
Dark Reactions con’t.Step two
ReductionATP and NADPH are
used to rearrange the two 3-carbon molecules of PGA
Dark Reactions con’t.Step three
Regeneration of RuBP
Two of the PGAL molecules are used to make glucose
The remaining PGAL is rearranged, with the help of ATP, to RuBP
Photosynthesis Overview
Alternative pathwaysC3 plants
Fix carbon to RuBP via the enzyme rubisco
Rubisco is probably the most abundant enzyme on Earth
If CO2 levels drop then the Calvin Cycle is starved
Photorespiration
Alternative Pathways con’t.C4 plants
CO2 is fixed into a 4-carbon compound
The mesophyll cells store the CO2 to keep feeding the Calvin Cycle
Slows down photorespiration
Good method for plants in hot climates
Alternative Pathways con’t.CAM plants
Crassulacean acid metabolism
CO2 is gathered at night and stored
CO2 can be released to keep the Calvin Cycle running
Photorespiration decreases
Factors Affecting PhotosynthesisLight intensityCO2 levelsTemperature