photosynthesis

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