PHOTOSYNTHESIS

PHOTOSYNTHESIS

Photosynthesis-converts sunlight into chemical energy-very complex-general reaction:

6CO2 + 6H20 → C6H12O6 + 6O2

• Light from the sun is composed of wavelengths (colors

• The shorter the wavelength the higher the frequency, thus the higher the energy

• The longer the wavelength the lower the energy, thus the lower the energy

Sunlight (a.k.a. white light)-sunlight is actually white light made of all

wavelength colors-sunlight is visible light-different colors=different wavelengths of

lightThe Visible Spectrum

violet-blue-green-yellow-orange-red

380 nm 750 nm

The Electromagnetic Spectrum-This is what scientists call radiation waves-Radiation=energy that travels and spreads as it

goesExamples: X-rays, gamma rays, visible

light, microwaves, etc.

-The electromagnetic spectrum is organized according to wavelengths

-Wavelengths are measured in nanometers (nm)

-Gamma rays have the shortest wavelengths = 10-5 nm(highest frequency and energy)

-Radio waves have the longest wavelengths =103 nm(lowest frequency and energy)

PHOTONS-Photon=quantum=discreet amounts of light

energy-Photons are not objects, but each one has

a distinct amount of energyEx: violet photons contain almost twice as much energy as red photons

*violet wavelengths=380 nm=high frequency=high energy

*red wavelenghts=750 nm=low frequency=low energy

Chlorophyll (the photosynthetic pigment)

-Chlorophyll is a green photosynthetic pigment found in chloroplasts of plants

-There are two main types of chlorophyll(chlorophyll a and chlorophyll b)

-Green is the least effective color for photosynthesis because it is reflected

-What you see is reflected. -Everything else is absorbed

**Thus, red and blue are most effective for photosynthesis.

Absorption SpectrumsAbsorption spectrums are graphs that plot a pigment’s light absorption vs. wavelength

Absorption spectrum of chlorophyll

**Remember:Green wavelengths are between ~475 and 600 nm

Light energy and waterA. In photosynthesis, light energy is used to split

water moleculesB. This process is called photolysis = when a

chemical is broken down by photonsC. Water is split into hydrogen ions, oxygen and

electrons by photonsD. ATP is also producedE. ATP and H ions will be used to fix CO2 to make

organic moleculesF. Photosynthesis relies on water and sunlight for

its initial reaction

General photosynthesis information

A. There are light dependent and light independent reactions

B. Light dependent reactions require lightC. Light independent reactions do not

require light or darkness.-they are independent of light or

dark-DO NOT REFER TO LIGHT

INDEPENDENT REACTIONS AS DARK REACTIONS (darkness is not required)

ASSIGNMENT1. READ: Go to your notes or the book and

read the overview of photosynthesis. 2. Next draw the pictures on the overhead.

Make them large and leave room to add notes

Light Dependent ReactionsA. Light absorption

1. As chlorophyll absorbs light its electrons are raised to a higher energy level by photons at certain wavelengths

2. The electrons at higher energy levels are said to be excited electrons

3. The excited electrons cause the chlorophyll to become photoactivated

4. Photoactivation is the activation of a particular pigment’s electrons (It is caused by absorbing energy from photons.)

5. After photoactivation the electrons quickly return to their ground state

6. When electrons return to their ground state they give off a photon (discreet amount of energy)

7. The photon (energy) is released in the form of heat

8. This process explains the conversion of light energy into heat energy –( this loss of energy is known as _________and supports the ______law of thermodynamics)

B. Chlorophyll organization and light absorption

1. Chlorophyll is found in the thylakoids which are found in chloroplasts2. Within the thylakoids chlorophyll is arranged into groups called photosystems3. There are two photosystems:

-Photosystem I – best at 700nm (aka P700)

-Photosystem II – best at 680 nm (aka P680)

Excited electrons that have absorbed photons of light pass from molecule to molecule until they reach the chlorophyll at the center of the photosystem

**Both photosystems are identical chlorophyll a molecules, except that they interact with different proteins of the thylakoids

6. Excited electrons that have absorbed photons of light pass from molecule to molecule until they reach the chlorophyll at the center of the photosystem

7. The photosystem (the chlorophyll) will then pass the excited electrons to a chain of electron carriers

The photosystem (the chlorophyll) will then pass the excited electrons to a chain of electron carriers

C. Oxygen production1. Photosystem II absorbs light

2. Its electrons become excited

3. Photosystem II donates its electrons to an electron transport chain and the flow of electrons will generate an ATP molecule

4. Photosystem II has been oxidized (LEO)

5. To get the electrons back (that were donated) an enzyme in the center of photosystem II breaks a water molecule (photolysis)

1. Photosystem II absorbs light2. Its electrons become excited3. Photosystem II donates its electrons to an electron transport chain and the flow of electrons will generate an ATP molecule4.Photosystem II has been oxidized (LEO)5. To get the electrons back (that were donated) an enzyme in the center of photosystem II breaks a water molecule (photolysis)6. The water is split into hydrogen ions, oxygen and electrons 7. Electrons are donated to PS II (GER)8. Oxygen and hydrogen ions are byproducts9. Oxygen is released to the atmosphere10. The production of oxygen in photosynthesis is done by photolysis and requires sunlight

6. The water is split into hydrogen ions, oxygen and electrons

7. Electrons are donated to PS II (GER)

8. Oxygen and hydrogen ions are byproducts

9. Oxygen is released to the atmosphere

10. The production of oxygen in photosynthesis is done by photolysis and requires sunlight

GET A BOOK FOR YOUR TABLE

D. ATP Production

1. an excited electron from the center of PS II is donated and passed along a chain of electron carriers

2. The energy for ATP is generated via a proton gradient that is created as electrons move through an ETC (chemiosmosis)

3. ATP is eventually formed when the H+ ions move through ATP synthase

**their energy is harnessed to bring a phosphate group and ADP

together –what is that called ________

4. The electrons from PS II are eventually donated to PS I (after they go through the ETC)

5. When ATP is produced in this manner it is called non-cyclic photophosphorylation(There is another way to produce ATP but we won’t learn that)

E. NADPH Production1. NADPH = nicotinamide adenine dinucleotide phosphate-oxidase2. After PS I accepts the electrons that were donated by PS II (the ones that went through the ETC), PS I becomes photoactivated3. Next PS I donates its excited electrons to Ferrodoxin via another ETC4. Ferrodoxin is an enzyme that assists in the formation of NADPH

5. The formation happens when NADP+ accepts two excited electrons from PS I and a H+ ion from the stroma

6. NADPH is then formed

NADP+ + H+ + 2E-ferrodoxin NADPH

The purpose of NADPH and ATP production is to provide power and chemical energy to drive the Calvin cycle (to make sugar)

**Remember in the chloroplast. . .** 1. Chemiosmosis involves the pumping of H+

ions through the membrane.2. The protons go from the stroma to the

thylakoid space. 3. This creates a proton gradient. 4. The protons later flow through ATP synthase

(back to the stroma) and their energy is captured in order to join a phosphate with ADP

5. This produces ATP.

Assignment#1. Draw and label a chloroplast.

-Include: grana thylakoids thylakoid membrane stroma double membrane

HOMEWORK

Complete the picture you started. Add color

Complete question 1-6 on pp.227Complete sentences and complete

answers. This assignments really counts!

Light-independent reactions(light not required)

A. Calvin cycle-1. takes place in the stroma2. begins with a 5 carbon sugar called ribulose biphosphate3. Ribulose biphosphate = RuBP4. ATP and NADPH from the light dependent reactions drive the Calvin cycle5. ATP provides the energy6. NADPH provides reducing power

7. RuBP is a carbon dioxide acceptor8. The reaction is catalyzed by the enzyme ribulose

biphosphate carboxylase9. RuBP carboxylase=rubisco10. 3RuBP and 3CO2 form:

6 3-Phosphoglycerate11. ATP is broken down to convert

6 3-Phosphoglycerate to 6 1,3-Biphosphoglycerate

12. NADPH reduces 6 1,3-Biphosphoglycerate to 6 Glyceraldehyde 3-phosphate

13. Only one of the G3P molecules will be converted to glucose, sucrose, starch, fatty acids or amino acids

14. Five G3P molecules will be converted back to RuBP to keep the Calvin cycle continuing

Calvin cycle (more info.)

A. Carbon is:-absorbed as carbon dioxide-released as sugar

B. ATP=energy for reactions NADPH=reducing agentC. Net sugar production per turn (3 carbon

dioxide and 3 RuBP) is 1 G3P.

Phases of the Calvin CycleA. Carbon fixation:

1. Every RuBP is attached to a CO2

3RuBPRubisco

3CO2(a 5 carbon

sugar)

converts to a very unstable6 carbon molecule that isimmediately converted to 6 3-carbon molecules

6 glycerate-3-phosphate

**For every RuBP and CO2 pair, two three carbon molecules are formed

3RuBP + 3CO2 → 6 glycerate-3-phosphate

B. Reduction1. molecules of glycerate-3-phosphate are phosphorylated to glycerate-1,3-biphosphate

*when ATP is hydrolyzed to ADP2. glycerate-1,3-biphosphate is reduced when NADPH donates its electrons

*NADPH→NADP+3. 6 molecules of triose-phosphate are produced

*one is removed from the Calvin cycle and used by the plant to produce sugar*the other 5 are recycled back into the Calvin cycle and converted back to 3RuBP

C. Regeneration (of RuBP)1. 5 triose-phosphate (G3P) molecules go through a complex series of reactions to form 3 RuBP2. The Calvin cycle starts over3. CO2 will be received by RuBP again

More on the Calvin Cycle

A. Start with 15 total carbons in 3 RuBP *Remember RuBP is a 5 C molecule

B. 3 CO2 is added for a total of 18 carbonsC. 1 triose-phosphate (G3P) is released (a 3 C

molecule is released)D. The other 5 triose-phosphate molecules are

recycled back into 3RuBP(15 C are recycled)

E. Net gain of carbons=3 (the single triose phosphate that was released)

F. Energy consumed during the Calvin cycle =9 ATP and 6 NADPH

G. ATP and NADPH will regenerate in the light-dependent reaction

H. There must always be light dependent reactions for light independent reactions to occur

I. The products of the light reactions are used as fuel for the Calvin cycle

1. Outline photosynthesis (light-dependent and light-independent)

2. Explain how the light-independent reaction depends on the light –dependent reaction

Limiting Factors in Photosynthesis

A. For photosynthesis to occur the following criteria must be met:

-suitable temperature-presence of: chlorophyll

light carbon dioxide water