PHOTOSYNTHESISPHOTOSYNTHESISThe Process That Feeds the

Biosphere•All organisms either directly or indirectly depend on photosynthesis

•Autotrophs-Produce organic molecules from CO2 & other inorganic materials

•Heterotrophs-

*Plants, algae, & some protists are photoautotrophs, they use light to synthesize glucose

Depend on organic compounds produced by other organisms

“self-feeders” Consumers

All heterotrophs depend on autotrophs for food and the oxygen that’s a

biproduct of photosynthesis

Photosynthsis Converts Light Energy to Chemical Energy

of FoodWhich organelle is responsible for photosynthesis??

Chloroplasts

What is the chemical energy that autotrophs produce??Glucose

What are the raw materials that go into photosynthesis? What are the products?6CO2+ 6H2O+ Light Energy C6H12O6+ 6O2

Which plant organ is the primary site of photosynthesis?Leaves

Anatomy of the Leaf & Its Chloroplasts

How do we know what we know about

photosynthesis??Tracking Atoms:The overall chemical reaction of photosynthesis is the reverse of cell respiration, but the process of photosynthesis is NOT the reverse of cell respiration:

What’s the equation for cell respiration?

C6H12O6 + 6O2 6CO2 + 6H2O + ATP energy

What’s the equation for photosynthesis?

6CO2 + 6H2O + light energy C6H12O6 + 6O2

If you don’t already have these equations memorized, write them down and commit them to memory!!

Sunlight

Photosynthesis

Cellularrespiration

Heat

Relationship Between Cell Respiration & Photosynthesis

Photosynthesis Equation in its Simplest Form:

CO2 + H2O [CH2O] + O2

General formula for a carbohydrate

The Splitting of WaterThe Splitting of WaterBefore the 1930’s, it was widely believed that the O2

produced by plants is a result of the splitting of CO2 during photosynthesisThanks to C.B. van Niel & others, we now know that the O2 produced is a result of the splitting of a water molecule during photosynthesis:

Van Niel’s Experimental ResultsSulfur bacteria: CO2 + 2H2S [CH2O] + H2O + 2S

Plants: CO2 + 2H2O [CH2O] + H2O + O2

General: CO2 + 2H2X [CH2O] + H2O + 2X

Conclusion: photosynthetic organisms require a hydrogen source which is split during

photosynthesis

Later Tests Using Oxygen-18 Isotope Markers Confirmed the

Same….Exp #1: When the oxygen in water is labeled…CO2 + 2H2O [CH2O] + H2O + O2Exp #2: When the oxygen in carbon dioxide is labeled…

CO2 + 2H2O [CH2O] + H2O + O2

Tracking Atoms Through Photosynthesis….

Quick Think

• With someone near you, discuss: With someone near you, discuss: where does the oxygen released where does the oxygen released from plants during photosynthesis from plants during photosynthesis come from and how did scientists come from and how did scientists determine thisdetermine this? ?

• Be prepared to share your ideas.Be prepared to share your ideas.

Photosynthesis as a Redox Photosynthesis as a Redox ProcessProcessCell Resp Photosynthesis

Employs redox reactions

Employs redox reactions

e- lose potential energy as they move down ETC

e- gain potential energyrequires energy from light

By-product = H2O By-product = O2

Gain or Lose?

Gain orLose?

? ?

Photosynthesis Overview

Go to your diagrams

Two Stages of Photosynthesis: Light

Reactions & Calvin CycleLight Reactions:

•Light is absorbed by chlorophyll•Energy from the light splits H2O•H from water reduces NADP+ (an e- acceptor) to NADPH•Chemiosmosis makes ATP from ADP. This process is known as photophosphorylation

•Products of light reactions:Energy = ATP & NADPHBy-product = O2

Occurs in thylakoid

Two Stages of Photosynthesis: Light

Reactions & Calvin CycleThe Calvin Cycle:•CO2 from atmosphere enters chloroplast & is incorporated into organic molecules = carbon fixation•NADPH from the light rxns reduces the fixed carbon (by donating H) to carbohydrate; ATP from light rxns is required for this step

•Product of Calvin Cycle:glucose

Occurs in stroma

The Light Reactions of

Photosynthesis

The Light Reactions Convert Solar Energy to the Chemical

Energy of ATP & NADPHThe Nature of Sunlight (electromagnetic energy):

•Light has properties of both waves & particles (photons)•Visible light is the part of the EMS that drives photosynthesis

•The shorter the wavelength, the higher the energy

Photosynthetic Pigments are Light Receptors

•Pigments like chlorophyll either absorb, transmit, or reflect light•The wavelength of light that is reflected is the color that we detect with our eyes•Which wavelength (color) of Light is least effective for Photosynthesis??Green

These accessory pigments allow chloroplasts to take advantage of a broader spectrum

Quick Think

•With someone near With someone near you discuss: you discuss: Why are Why are plants greenplants green? ?

•Be prepared to share Be prepared to share your thoughtsyour thoughts

Excitation of Chlorophyll by Light

•Energy from a photon of light raises a pigment molecule’s e- from ground state to an unstable excited state •When the e- drops back down to its ground state, energy is emitted in the form of heat & light•Chloroplasts in plants don’t fluoresce because the excited e- is passed to an e- acceptor rather than dropping back down to ground state

Go to your diagrams

A photosystem is a bundle of pigment molecules and

proteins•Photosystems act as an antenna for light

Made of 2 chlorophyll a molecules & a primary e- acceptor

Special because they can use light to boost an e- to the next energy level…light energy has now been converted to chemical energy

The thylakoid has 2 photosystems: PS I & PS II

Chlorophyll a molecules that best absorb light at 680 nm & 700 nm respectively

Noncyclic Electron Flow: PS I & PS II work together to use light to make ATP &

NADPH during the light reactionsDuring the light reactions, e- may flow in either a cyclic or noncyclic manner:Noncyclic flow of e-

plastoquinone

plastocyanin

Noncyclic Electron Flow: PS I & PS II work together to use light to make

ATP & NADPH during the light reactions

http://www.cst.cmich.edu/users/baile1re/bio101fall/enzphoto/photoanima.htm#

http://www.stolaf.edu/people/giannini/flashanimat/metabolism/photosynthesis.swf

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html#

Animation of steps:

Noncyclic flow of e-

Go to your diagrams

Quick Think

• With someone near you,With someone near you, summarize summarize the steps of noncyclic electron flow the steps of noncyclic electron flow in the light reactionsin the light reactions

Cyclic Electron Flow: uses PS I but not PS II

During the light reactions, e- may flow in either a cyclic or noncyclic manner:

•Only ATP is produced, not NADPH

Cyclic e- Flow•Noncyclic e- flow produces NADPH & ATP •BUT the Calvin cycle uses more ATP•SO Cyclic e- flow is used to keep up with the ATP demand so that the Calvin cycle doesn’t stop

Go to your diagrams

Quick Think

• With someone near you, discuss the differences between noncyclic and cyclic electron flow

Comparing Chemiosmosis in

Mitochondria and Chloroplasts

Comparing Chemiosmosis in Chloroplasts & Mitochondria

In both organelles, the ETC pumps H+ ions from an area of low concentration to an area of higher concentration. The diffusion of H+ through ATP synthase drives ATP synthesis

Similarities

Comparing Chemiosmosis in Chloroplasts & MitochondriaDifferences

•In mitochondria chemical energy from food is transferred to ATP & NADH. •In Chloroplasts light energy is transfered to ATP & NADPH• H+ diffuse across inner

membrane to matrix in the mitochondrion•H+ diffuse out of the thylakoid & into the stroma of the chloroplast.