PHOTOSYNTHESIS

WEEK 9Text pages 117-132

(CHAPTER 7)

How do plants respire?

PHOTOSYNTHESIS!!

The sun is the source of energy for producing carbohydrates in plants

Energy flow occurs through a series of electron transfers and oxidationreduction reactions in the chloroplasts of plant cells

Photosynthesis v Cell RespirationPhotosynthesis

-Thylakoid discs-ETC in thylakoid

energized by sun-H+ electrochemical

gradient-Calvin Cycle-NADPH

Cell Respiration

-Cristae-ETC in cristae energized by

glucose e-

-H+ electrochemical gradient

-Citric Acid Cycle-NADH

ETC= Electron Transport Chain

Photosynthesis

• Process of converting solar energy into chemical energy (carbohydrates)

• Organisms that produce their own food = autotrophs

• Autotrophs are producers- synthesize carbohydrates

• Heterotrophs are consumers

• Autotrophs and heterotrophs use carbs. synthesized by photosynthesis

PHOTOSYNTHESIS

CO2 + 2H2O (CH2O) + H2O + O2

CHEMICAL ENERGY OXYGEN IS RELEASED

SOLAR ENERGY

DURING PHOTOSYNTHESIS CARBON DIOXIDE IS REDUCED AND WATER IS OXIDIZED

REDUCTION- Gain Hydrogen/electronsOXIDATION- Lose Hydrogen/electrons REDOX

CO2 + 2H2O (CH2O) + H2O + O2

SOLAR ENERGY

x 6

6CO2 + 6H2O C6H12O6 + 6H2O + 6O2

SOLAR ENERGY

GLUCOSE

SOLAR ENERGY

• Solar energy is converted to ATP molecules

• ATP is used to REDUCE CO2 into carbohydrates

• Therefore, solar energy is not used directly

Simplified REDOX Rxn.-Photosynthesis

PHOTOSYNTHESIZERS

• Plants

• Algae

• Bacteria – Cyanobacteria– Blue/green “algae”

Eukaryotes

Eukaryotes

Prokaryotes

Importance of Photosynthesizers• Provide oxygen to sustain life!• O2 rises into atmosphere where it later becomes

OZONE (O3) which filters out harmful rays• Plant fossils coal, a “fossil fuel”• Fermentation of plant materials ethanol

(gasoline additive)• Lumber• Fabrics (cotton)• Paper• Pharmaceuticals• Beauty products• Plants are simply incredible !!

How/Where does Photosynthesis occur?

• The green portion of plants absorbs sunlight• CO2 enters plant leaf via small openings =

STOMATA• Roots of plant absorb H2O

• CO2 and H2O diffuse into CHLOROPLAST

• Photosynthesis occurs in chloroplasts

CHLOROPLASTS• Are organelles

• Located inside of plant cells

• Are surrounded by a double membrane

• Semi-fluid interior = STROMA

• The STROMA contains THYLAKOIDS

• THYLAKOIDS are membrane bound sacs

• THYLAKOIDS are the site of light dependent reactions

• THYLAKOIDS stack on top of each other to form GRANA

• THYLAKOIDS are connected to the space of all other thylakoids inside of the chloroplast which forms an inner compartment = THYLAKOID SPACE

http://sciencephoto.com/images/download_lo_res.html?id=670012430

Fig. 7.2 pg. 119

CHLOROPHYLL

• Found in the THYLAKOID MEMBRANE• Is a green pigment• Is a molecule• Absorbs solar energy

Chlorophyll a

Absorption of solar energy occurs at the THYLAKOID membrane/ GRANA

CO2 is reduced by enzymes to a carbohydrate in the STROMA

How is CO2 reduced to form a Carbohydrate?

• Electrons are needed to reduce CO2

• NADPH = nicotinamide adenine dinucleotide phosphate-oxidase

• NADP+ is the coenzyme of the REDOX rxn.

NADP+ + 2e- + H+ NADPH

REDUCTION OF NADP+

PHOTSYNTHESIS

TWO sets of reactions

1- THE LIGHT REACTIONS

2- THE CALVIN CYCLE REACTIONS

Light Reactions• Only occur during daylight hours

• Solar energy is used to energize electrons involved in the electron transport chain

• As electrons move from complex to complex, energy is released

• ATP is produced via the movement of electrons and release of energy as they move down the electron transport chain

• Energized electrons are taken up by NADP+

Light Reactions

SOLAR ENERGY CHEMICAL ENERGY

(ATP and NADPH)

CALVIN CYCLE REACTIONS

• Named for Melvin Calvin (nobel prize recipient)

• CO2 is taken up and then reduced to a carbohydrate that is later converted to glucose

• The ATP and NADPH from the light reaction are used to REDUCE CO2

CALVIN CYCLE REACTIONS

CHEMICAL ENERGY CHEMICAL ENERGY

(ATP and NADPH) (Carbohydrate)

Overview of Photosynthesis

SOLAR ENERGY CHEMICAL ENERGY CHEMICAL ENERGY

ATP and NADPH Carbohydrate

Steps of PHOTOSYNTHESIS

1- SOLAR ENERGY is absorbed by the THYLAKOID/ GRANA

2- H2O is split and O2 is released

3- ATP and NADPH are produced

4- CO2 is taken up at the STOMATA

5- CO2 is reduced to carbohydrate (CH2O) using ATP and NADPH from the light rxns.

LightRxn.

CalvinCycleRxn.

Light is absorbed by the THYLAKOID/ GRANACarbon Dioxide enters the chloroplast via the STOMATAThe Calvin Cycle occurs in the STROMA

Visible Light/Absorption Spectrum

• Visible light- ROYGBIV• Visible light is most prevalent in the environment• Ozone (O3) protects us from high energy wave lengths• Chloroplast pigments absorb only some wavelengths

within their absorption spectrum• Chlorophyll a and b are important in photosynthesis

and absorb, violet, blue and red light• Green light is transmitted and reflected by chlorophyll,

therefore plants appear green to us– All light reflected = white– All light absorbed = black– Reflection of a particular color= the color you see !!

Fig. 7.6- pg. 122

CAROTENOIDS- pigment molecules in plants that give shades of yellow and orange (fall foliage colors) by absorbing violet-blue-green

The Light ReactionsA Detailed View

Begins with Photosystem II (PSII)Photosystem- contains:1- pigment complex (chlorophyll a, b and

carotenoids) 2- An electron acceptor moleule w/in the

THYLAKOID memebraneDuring the light rxn., electrons follow a

NONCYCLIC pathway beginning at PSII

1. Solar Energy is captured by PSII

2. H20 is split, releases electrons and O2

3. Electrons are passed to PSII

4. Electrons concentrate at the Reaction Center located in chlorophyll a

5. The Reaction Center “energizes” the e-

6. The e- are accepted by and e- acceptor

Fig. 7.7 pg. 123

1.

2.

3.

Water is oxidized, O2 is released (Mito.)Hydrogen stays in thylakoids to create H+ gradient

4./5.

6.

ATP7./8.

7. Electrons move along the electron transport chain and H+ forms a gradient by staying in theThylakoid space.

8.ATP is produced when H+ ions go through the ATPSynthase complex. ATP is used in the Calvin Cycle to reduce CO2 to carbohydrates

9.Solar energy is absorbed by PSI

10.Excited electrons are captured by the electron acceptor(low energy electrons from the ETC are captured by PSI andare then “excited” by the electron acceptor

11.2 electrons from PSI are passed to NADP+ A hydrogen ion is also added to NADP+ which gets REDUCED to NADPH

12. NADPH is used in the Calvin Cycle along with ATP

9.

10.

11.

12.

THE THYLAKOID MEMBRANE

Fig. 7.8 pg. 124

The Light Reaction Review

• Occurs in the THYLAKOID MEMBRANE• Inputs= Water and Sunlight• Involves PS II, the electron transport chain and PSI• ATP is produced via the ETC and CHEMIOSMOSIS• NADPH is produced via the reduction of NADP+

via electrons released from PSI• Electrons from the ETC ‘feed’ PSI• END PRODUCTS OF LIGHT RXN = ATP and NADPH

The Calvin Cycle Reactions

• A series of reactions that occur in the STROMA of chloroplasts

• Uses CO2 from the atmosphere to produce carbohydrates

• CO2 is reduced using ATP and NADPH to form carbohydrates

STEPS of the CALVIN CYCLE

1- Carbon Dioxide fixation- CO2 from atmosphere attaches to RuBP (ribulose-1,5-bisphosphate), a 5-Carbon molecule a 6-C molecule splits into TWO 3-C molecules (3PG- 3-Phosphoglycerate)- This rxn. is sped up by RuBP carboxylase (enzyme)

2- CO2 reduction

3- Regeneration of RuBP

Fig. 7.9 pg. 126

RuBP is usedAnd regeneratedIn the cycle

2. CO2 REDUCTION

From the lightRxns. G3P is also

known as PGAL

G3P is END PRODUCT of Calvin Cycle

Fig. pg. 127

3. Regeneration of RuBP

G3P (Glyceraldehyde-3-Phosphate)

G3P is the end product of the Calvin Cycle

G3P can be converted into other moleculesG3P

Fatty Acid SynthesisAmino Acid Synthesis

GlucosePhosphate

+ FructosePhosphate

SUCROSE

STARCH

CELLULOSEPlants use sucrose to transport carbohydrates from one part of the plant to the other

(Storage form of glucose)

(Structural carbohydrate)

Plant oils

Calvin Cycle Review• The Cycle begins when CO2 from the atmosphere

enters the chloroplasts via the STOMATA of the leaves

• CO2 is fixed by RuBP to form TWO 3-Carbon molecules called 3PG

• CO2 is reduced via the oxidation of ATP and NADPH (from the light cycle) to form G3P

• G3P is converted into other organic molecules (glucose, sucrose, cellulose, starch, amino acids, fatty acids)

• RuBP is regenerated• G3P is the end product of the Calvin Cycle

OTHER TYPES OF PHOTOSHYTHESIS1. C3 Photosynthesis

- Normally, C3 plants use RuBP Carboxylase following CO2 fixation to form Two 3PG molecules in mesophyll cells

- Stomata open and close to regulate the influx of CO2

- When stomata close (hot days), O2 increases due to photosynthesis RuBP combines with O2 with the help RuBP carboxylase instead of CO2 only 1 molecule of 3PG is produced along w/phosphoglycolate(a toxic 2-Carbon molecule) and CO2 is released = PHOTORESPIRATION

- PHOTORESPIRATON is not efficient and is wasteful and is not part of the Calvin Cycle!!

Yields 1 3PG molecule

And

1 Phosphoglycolate molecule (TOXIC!)

2. C4 Photosynthesis- Contain bundle sheath cells and mesophyll cells (both contain chloroplasts)- The mesophyll cells are arranged concentrically around the bundle sheath cells- C4 plants use enzyme PEP carboxylase (PEPCase) to fix CO2 and PEP (phosphoenolpyruvate) OXALOACETATE-Oxaloacetate is then reduced to malate in mesophyll cells which pump malate and CO2 into the bundle sheath cells- CO2 then enters the Calvin Cycle in the bundle sheath cells-C4 plants avoid photorespiration!! (sugarcane, corn, bermuda grass- evolved in high temps)

WHY?• B/c PEPCase does not bind with O2! CO2 is able to go to the Calvin

Cycle• CO2 is not able to go to the Calvin Cycle in C3 plants when they shut

their Stomata!

OTHER TYPES OF PHOTOSHYTHESIS

Even when STOMATA are closed, CO2

is delivered to the Calvin Cycle in C4 plants

The C4 Pathway

Why are C4 Plants able to continue on with the Calvin Cycle even when their

Stomata are closed?

Which came first evolutionarily,C3 or C4 plants?

OTHER TYPES OF PHOTOSHYTHESIS3. CAM Photosynthesis“Crassulacean-acid Metabolism”-CAM photosynthesizers partition rxns. based on time of day-Only open stomata at night! (conservesWater)-At night, CAM plants use PEPCase

to fix some CO2 to form 4-C molecules (malate)-Malate is stored in plant vacuoles in mesophyll cells- During the day, the malate releases

CO2 to the Calvin Cycle when ATP and NADPH are available from the light rxns.-CAM plants are able to live in stressful conditions!

CAM occurs in flowering plants and variousother plant groups

Types of CAM Plants

Agavaceae agaves, yucca

Cactaceae cacti

Liliaceae some of the lilies

Euphorbeace spurges

Orchidaceae some orchids

Polypodieace some ferns

Portulaceae purslanes

Vitacea few grapes

Weltiwitschiaceae our favorite odd gymnosperm of Nabim desert

Family Familiar Names

Plants: An Evolutionary PerspectivePlants have adapted to their environment over thousands of years

First land plants evolved approx. 430-440 mya

Each type of photosynthesis has its advantages and disadvantages

C4 plants most likely evolved in areas of high light intensities, high temps and little rainfall and are more sensitive to cold

C3 plants function better than C4 plants below 25 degrees Celcius.

CAM plants copete well with either type of plant in arid (lack of water) environments

If plants evolved 430 mya and the first fishes evolved 500 mya

where did Oxygen come from for the survival of the fishes?

CYANOBACTERIA

Evolved approximately 2-2.5 billion years agoOxygenated the earth’s oceansCyanobacteria are photosynthetic bacteria!Cyanobacteria FIX CARBON DIOXIDEFound in oceans and fresh water

Banded iron formations, found worldwide in rocks mostly dating to between 2 billion years ago to 2.5 billion years ago, are evidence of the oxygenation of the Earth's oceans by cyanobacteria.

Stromatolites (early corals) such as these are columns produced by and containing cyanobacteria. They are found in the fossil record up to over 2 billion years ago, and some may date to as old as 3.5 billion years.

Eukaryotic Phytoplankton

- Diatoms and Dinoflagellates- Use photosynthesis for energy- Fix up to 44% of AtmosphericCO2 !!- Are less abundant than cyanobacteria- Are larger than cyanobacteria15th April 2010 in the Journal of the International Society for Microbial Ecology. Authors Dr. Rory Howlett and Zubcov

How does global warming impact Carbon Fixation?

Rates of carbon exchange are expressed as 1012 kg yr−1.

We depend on ocean uptake and sedimentation of CO2 to keep the carbon cycle in balance

With added CO2, we are disrupting the natural system and the earth’s natural processes are not able to keep up with the volume of added CO2

The concentration of CO2 in the atmosphere increases causing global warming

GLOBAL WARMING

What happens when CO2 levels rise?

CO2, a greenhouse gas, will trap heat and the earth’s global temperature risesHigh temperatures melt glaciersHigh temperatures disrupt natural weather patterns

As temperatures rise, the deep bottom water upwelling begins to slow

This causes higher sea surface temperatures and lower ocean CO2 emissions(marine organisms are affected along with the CO2 ocean pump)

The conveyor belt and ocean currents slow down and weather patterns are altered!!

Why Preserve Tropical Rainforests?

They substantially reduce the amount of CO2 in the atmosphere

Rainforest total global surface area has decreased from 14% to 6%

What can you do??Take public transportation

Reduce your use of products that are produced via the burning of fossil fuels (ex. Plastic bags)

Educate yourself and educate others

“Reduce, Reuse, Recycle”

SPEAK UP! “Excuse me, I think you dropped something!”

Homework

Read CHAPTER 10 pages 152-179

Read page 380 chpt. 21

Do self test for chapter 10