Photosynthesis is carried out by a number of different organisms

All contain chlorophyllo Absorbs light energy and

begins process of photosynthesis

o Chlorophyll a (blue green)

o Chlorophyll b (yellow green)

o They absorb different wavelengths of light

Make up largest group of photosynthesizing prokaryotes

First organisms to harness the sun’s energy

Unicellular, but may grow in colonies

Live in many different environments

Grow rapidly in nutrient rich water (known to cause algal blooms)o can be toxic to fish, birds,

humans, and other mammals

Unlike cyanobacteria, algae, some protists, and plant cells contain chlorophyll within the photosynthetic membranes of discrete organelles called chloroplastso gives leaves, stems

and un-ripened fruit their characteristic green colour!

Colour Code! Leaves

o The Factory! Transpiration

o Cooling and Transport

Stomatao The Gate Keepers

Typical plant cell chloroplast approx. 3um to 8um in length and 2 um to 3 um in diameter

Have two limiting membranes (outer and inner) enclosing an interior space filled with a liquid stroma

Within the stroma, a system of membrane bound sacs called thylakoids stack on top of one another to form characteristic columns called granao typical chloroplast has 60 grana each consisting of 30-50

thylakoids Adjacent grana connected to one another by unstacked

thylakoids called lamellae Inside the thylakoids is a water filled space called the Lumen Chloroplasts have there own DNA and ribosomes, reproduce

via fission

http://www.youtube.com/watch?v=Oi2_n2wbB9o&feature=related

Converts light energy into the chemical bonds of glucose (plants are Autotrophs).

It is an endergonic rxn that happens in two stages: The Light Dependant Rxn and the Light-Independent Rxn.

The overall rxn is:

6CO2 + 6H2O + Light Energy C6H12O6 + 6O2

Glucose

Occurs in the Thylakoid Membrane The chlorophyll captures light energy and uses it

to break down water molecules and create ATP and NADPH.

The oxygen is released as a product. The ATP and NADPH are carried over to the Light

Independent Rxn.

Occurs in the stroma CO2 from the air is added to the H+ ions

(carried by NADPH) the glucose is formed

http://www.youtube.com/watch?v=cX3Iev-JDgM

6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O

The sugars that result from photosynthesis are produced by adding

the hydrogen ions and electrons from water to carbon dioxide, NOT

by splitting CO2 and adding water!

oxidized

reduced

H+ and e-

Involves the splitting of water (photolysis) 12 H2O + Energy 6 O2 + 24 H+ + 24e-

Requires light for the energy to split the water molecule

Also forms a highly energetic compound, adenosine triphosphate (ATP)

3 Parts:o 1. PHOTOEXCITATIONo 2. ELECTRON TRANSPORTo 3. CHEMIOSMOSIS

http://vcell.ndsu.nodak.edu/animations/photosynthesis/movie-flash.htm

Chlorophyll A is the most important photosynthetic pigment.

Other pigments called antenna or accessory pigments are also present in the leaf.o Chlorophyll Bo Carotenoids (orange / red)o Xanthophylls (yellow / brown)

These pigments are embedded in the membranes of the chloroplast in groups called photosystems.

Each pigment absorbs a particular wavelength of light in the visible spectrum

What wavelengths of light do you think plants use the least in photosynthesis?

Photon = Packets of electromagnetic radiation Occurs in Photosystems (clusters of photosynthetic

pigments embedded in the thylakoid membranes Photosystems absorb photons of particular

wavelengths Consist of an antenna complex and rxn centre

Two types: 700, 680 refers to wavelength absorbed (nm)o PS I (P700)o PS II (P680)

Antenna complex absorbs a photon of light Transfers the energy from pigment to pigment

until it reaches a chlorophyll a molecule in the centre of the rxn centre

The electron of this chlorophyll moves from ground state to a higher potential energy level (excitation)

ETC!1. Photon strikes PS II, excites electron

o Usually, excited electron is captured by the primary electron acceptor (REDOX rxn)

o Electron then transferred to Plastoquinone (PQ) aka Q cycleo Then to ETC similar to Cell Respo Process occurs twice, so 2 electrons

2. A Z protein associated with PS II splits water into oxygen, protons, electronso Oxygen leaves chloroplast as a by-producto 2 electrons used to replace those that have left PS IIo Protons remain in Thylakoid space, contributing to H+

gradient that drives chemosmosis

3. Electrons pass through the Q cycle which transports protons into lumen from stroma, adding to H+ gradient (4 protons for every 2 electrons), then through the b6 –f complexo Electrons then move through Plastocyanin (Pc), eventually

replacing two electrons lost from PS I when it was struck by photons.

4. Electrons from PS I pass through another ETC containing ferredoxin (Fd)o They then move to the enzyme NADP reductase that uses

the two electrons and protons from the stroma to reduce NADP+ to NADPH

3. Chemiosmosis – Protons that have accumulated in the lumen cause electrochemical gradient that drives phosphorylation of ADP to ATPo Called photophosphorylation, since light is required

o Page 166 #2,3,4,6

Calvin Cycle Also called C3 photosynthesis (since first

compound formed is a 3C molecule Occurs in stroma of chloroplasts Cyclic series of reactions Three phases: carbon fixation, REDOX reactions,

RuBP (ribulose 1,5-bisphosphate) regeneration

Phase 1: Carbon Fixationo CO2 are added to RuBP, forming 3 unstable 6C intermediate

moleculeso Each of these instantly splits into two 3C molecules called

PGA (3 phosphoglycerate) for a total of sixo The enzyme that catalyses these reactions is called Rubisco,

a very large enzyme that works very slowly, most abundant protein on earth

Phase 2: REDOXo Each of the six PGA is phosphorylated by 6 ATP to form six

1,3bisphosphoglycerateo 6 NADPH molecules each use a pair of electrons to produce

six G3P (glyceraldehyde 3 – phosphateo One molecule of G3P exits as a final product

Phase 3: RuBP regenerationo The five G3P are rearranged to regenerate 3 RuBPo 3 ATP are used!

http://www.youtube.com/watch?v=_NIhg1qa_L0

The Bottom Lineo For the net synthesis of one G3P, 9 ATP and 6 NADPH

are used!

o Page 167, #9,10,11

Is the primary end product of photosynthesis It may be converted into glucose and polymerized

into starch w/in the stroma Or it may be transported to the cytoplasm and

used to produce glucose and sucrose. Sucrose is the main carb transported from

mesophyll cells of the leaf to other cells of the plant

Rubisco – the double agent! Normally rubisco adds CO2 to RuBP but when O2 is very

plentiful it adds it to RuBP This is called Photorespiration – it occurs in light! It removes PGA molecules from the Calvin cycle Produces phosphoglycolate Decrease CO2 fixation and less sugar formed Carbon fixation 4X that of oxygen fixation (20% loss of C) Rubisco is an evolutionary remnant (from a time in earth’s

history when O2 was not a prevalent Some plants have adapted strategies to work around this!

HELPFUL! ANNOYING!!

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Hot, dry environments C4 photosynthesis – a pathway of carbon fixation

that reduces the amount of photorespiration that takes place by continually pumping CO2 molecules from mesophyll cells into bundle sheath cells, where rubisco brings them into the C3 Calvin cycle

C4 refers to the four carbon oxaloacetate that is formed in the mesophyll

CO2 level in leaf is increased, no photoresp.

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Crassulacean Acid Metabolism Plants in dry, desert environments Stomata open at night to take in CO2 and

incorporate it into organic acids, and close during the day to allow the acids to release CO2 into the Calvin Cycle.

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Light Intensity (P173) Temperature (P174) O2 concentration (P175) Efficiency (P175)

Page 178 1-5

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