Photosynthesis
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PHOTOSYNTHESIS. WEEK 9 Text 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 oxidation

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Photosynthesis

PHOTOSYNTHESIS

WEEK 9

Text pages 117-132

(CHAPTER 7)


How do plants respire

How do plants respire?

PHOTOSYNTHESIS!!


Photosynthesis

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

Energy flow occurs through a series of electron transfers and oxidation

reduction reactions in the chloroplasts of plant cells


Photosynthesis v cell respiration

Photosynthesis v Cell Respiration

Cell Respiration

-Cristae

-ETC in cristae energized by glucose e-

-H+ electrochemical gradient

-Citric Acid Cycle

-NADH

Photosynthesis

-Thylakoid discs

-ETC in thylakoid energized by sun

-H+ electrochemical gradient

-Calvin Cycle

-NADPH

ETC= Electron Transport Chain


Photosynthesis1

Photosynthesis

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

  • Organisms that produce their own food = autotrophs

  • Autotrophs are producers- synthesize carbohydrates

  • Heterotrophsare consumers

  • Autotrophsandheterotrophsuse carbs. synthesized by photosynthesis


Photosynthesis2

PHOTOSYNTHESIS

SOLAR ENERGY

CO2 + 2H2O (CH2O)+ H2O + O2

CHEMICAL ENERGY

OXYGEN IS RELEASED

DURING PHOTOSYNTHESIS CARBON DIOXIDE IS REDUCED AND WATER IS OXIDIZED

REDUCTION- Gain Hydrogen/electrons

OXIDATION- Lose Hydrogen/electrons

REDOX


Photosynthesis

SOLAR ENERGY

CO2 + 2H2O (CH2O)+ H2O + O2

x 6

SOLAR ENERGY

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

GLUCOSE


Solar energy

SOLAR ENERGY

  • Solar energy is converted to ATP molecules

  • ATP is used to REDUCECO2 into carbohydrates

  • Therefore, solar energy is not used directly


Simplified red ox rxn photosynthesis

Simplified REDOXRxn.-Photosynthesis


Photosynthesizers

PHOTOSYNTHESIZERS

  • Plants

  • Algae

  • Bacteria

    • Cyanobacteria

    • Blue/green “algae”

Eukaryotes

Eukaryotes

Prokaryotes


Importance of photosynthesizers

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

How/Where does Photosynthesis occur?

  • The green portion of plants absorbs sunlight

  • CO2 enters plant leaf via small openings = STOMATA

  • Rootsof plant absorb H2O

  • CO2 andH2O diffuse into CHLOROPLAST

  • Photosynthesis occurs in chloroplasts


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


Photosynthesis

Fig. 7.2 pg. 119


Chlorophyll

CHLOROPHYLL

  • Found in the THYLAKOIDMEMBRANE

  • Is a green pigment

  • Is a molecule

  • Absorbs solar energy

Chlorophyll a


Photosynthesis

Absorption of solar energy occurs at the THYLAKOID membrane/ GRANA

CO2 is reduced by enzymes to a carbohydrate in the STROMA


How is co 2 reduced to form a carbohydrate

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 REDOXrxn.

REDUCTION OF NADP+

NADP+ + 2e- + H+ NADPH


Photsynthesis

PHOTSYNTHESIS

TWO sets of reactions

1- THE LIGHT REACTIONS

2- THE CALVIN CYCLE REACTIONS


Light 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 reactions1

Light Reactions

SOLAR ENERGYCHEMICAL ENERGY

(ATP and NADPH)


Calvin cycle reactions

CALVIN CYCLE REACTIONS

  • Named for Melvin Calvin (nobel prize recipient)

  • CO2is 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 REDUCECO2


Calvin cycle reactions1

CALVIN CYCLE REACTIONS

CHEMICAL ENERGY CHEMICAL ENERGY

(ATP and NADPH) (Carbohydrate)


Overview of photosynthesis

Overview of Photosynthesis

SOLAR ENERGYCHEMICAL ENERGYCHEMICAL ENERGY

ATP and NADPH Carbohydrate


Steps of photosynthesis

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.

Light

Rxn.

Calvin

Cycle

Rxn.


Photosynthesis

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/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 !!


Photosynthesis

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 reactions a detailed view

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 memebrane

During the light rxn., electrons follow a NONCYCLIC pathway beginning at PSII


Photosynthesis

Fig. 7.7 pg. 123

1.

  • Solar Energy is captured by PSII

  • H20is split, releases electrons and O2

  • Electrons are passed to PSII

  • Electrons concentrate at the Reaction Center located in chlorophyll a

  • The Reaction Center “energizes” the e-

  • The e- are accepted by and e- acceptor

6.

4./5.

3.

2.

Water is oxidized, O2 is released (Mito.)

Hydrogen stays in thylakoids to create H+ gradient


Photosynthesis

  • 7. Electrons move along the electron transport

  • chain and H+ forms a gradient by staying in the

  • Thylakoid space.

  • ATP is produced when H+ ions go through the ATP

  • Synthase complex. ATP is used in the Calvin Cycle to

  • reduce CO2 to carbohydrates

  • Solar energy is absorbed by PSI

  • Excited electrons are captured by the electron acceptor

  • (low energy electrons from the ETC are captured by PSI and

  • are then “excited” by the electron acceptor

  • 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

10.

11.

9.

7./8.

12.

ATP


The thylakoid membrane

THE THYLAKOID MEMBRANE

Fig. 7.8 pg. 124


The light reaction review

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

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

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 RuBPcarboxylase(enzyme)

2- CO2reduction

3- Regeneration of RuBP


Photosynthesis

RuBP is used

And regenerated

In the cycle

Fig. 7.9 pg. 126


2 co 2 reduction

2. CO2 REDUCTION

Fig. pg. 127

From the light

Rxns.

G3P is also

known as PGAL

G3P is END PRODUCT of Calvin Cycle


3 regeneration of rubp

3.Regeneration of RuBP


G3p glyceraldehyde 3 phosphate

G3P (Glyceraldehyde-3-Phosphate)

G3P is the end product of the Calvin Cycle

G3P can be converted into other molecules

G3P

Amino Acid Synthesis

Fatty Acid Synthesis

Glucose

Phosphate

Plant oils

STARCH

(Storage form of glucose)

+ Fructose

Phosphate

Plants use sucrose to transport

carbohydrates from one part

of the plant to the other

(Structural carbohydrate)

CELLULOSE

SUCROSE


Calvin cycle review

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 TWO3-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)

  • RuBPis regenerated

  • G3Pis the end product of the Calvin Cycle


Other types of photoshythesis

OTHER TYPES OF PHOTOSHYTHESIS

  • C3 Photosynthesis

    • Normally, C3 plants use RuBPCarboxylasefollowing CO2fixation 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 O2with the help RuBPcarboxylaseinstead of CO2  only 1 molecule of 3PG is produced along w/phosphoglycolate(a toxic 2-Carbon molecule) andCO2 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!)


Other types of photoshythesis1

OTHER TYPES OF PHOTOSHYTHESIS

  • 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 CO2and 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!


Photosynthesis

Even when STOMATA are closed, CO2

is delivered to the Calvin Cycle in C4

plants


The c4 pathway

The C4 Pathway


Why are c4 plants able to continue on with the calvin cycle even when their stomata are closed

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 photoshythesis2

OTHER TYPES OF PHOTOSHYTHESIS

  • CAM Photosynthesis

    “Crassulacean-acid Metabolism”

    -CAM photosynthesizerspartition rxns.

    based on time of day

    -Only open stomata at night! (conserves

    Water)

    -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 various

other plant groups


Types of cam plants

Types of CAM Plants

Family

Familiar Names


Plants an evolutionary perspective

Plants: An Evolutionary Perspective

Plants 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


Photosynthesis

If plants evolved 430 mya and the first fishes evolved 500 mya where did Oxygen come from for the survival of the fishes?


Cyanobacteria

CYANOBACTERIA

Evolved approximately 2-2.5 billion years ago

Oxygenated the earth’s oceans

Cyanobacteria are photosynthetic bacteria!

Cyanobacteria FIX CARBON DIOXIDE

Found in oceans and fresh water


Photosynthesis

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.

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.


Eukaryotic phytoplankton

Eukaryotic Phytoplankton

- Diatoms and Dinoflagellates

- Use photosynthesis for energy

- Fix up to 44% of Atmospheric

CO2 !!

- Are less abundant than cyanobacteria

- Are larger than cyanobacteria

15th 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

How does global warming impact Carbon Fixation?

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


Photosynthesis

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

GLOBAL WARMING


What happens when co 2 levels rise

What happens when CO2 levels rise?

CO2, a greenhouse gas, will trap heat and the earth’s global temperature rises

High temperatures melt glaciers

High temperatures disrupt natural weather patterns


Photosynthesis

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

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

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

Homework

Read CHAPTER 10 pages 152-179

Read page 380 chpt. 21

Do self test for chapter 10


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