This presentation will focus on:

The importance of autotrophs

An overview of photosynthesis

Leaf and chloroplast structure and function

The electromagnetic spectrum

Pigment function and variety

The Light Reactions

The Calvin Cycle

All organisms require a source of energy

All organisms require a source of carbon compounds

Provides molecular oxygen for the atmosphere

2 Types of Autotrophs:

Chemotrophs Photoautotrophs

6 CO2 + 6 H2O C6H12O6 + 6 O2

Plants are composed of three major organ systems:

The Root System anchors the plant in place

stores excess sugars

absorbs water and mineral nutrients

The Shoot System supports the plant body

provides passageway for nutrients and minerals

Leaves site of photosynthesis (food production)

Plant organs are made up of 3 types of tissues:

• Dermal• cells for structure and protection

• secretion of cutin to prevent water loss

• Ground• photosynthesis

• storage of food and water

• Vascular• specialized for transport of water and nutrients

http://www.botany.uwc.ac.za/ecotree/leaves/stomata.htm

http://www.fw.vt.edu/dendro/forestbiology/photosynthesis.swf

• The ultimate source of energy is the sun

• Solar energy is called electromagnetic radiation

• Travels in waves of photons

• The Electromagnetic spectrum describes the range of energy in solar radiation

• The EM spectrum is measured by wavelength

Pigments are organic molecules that absorb visible light

Wavelengths not absorbed are reflected, creating the visible color of an objectWavelengths absorbed cause the excitations of electrons Plants contain a major pigment, chlorophyll a, and accessory pigments like carotenoids and anthocyanins

http://earthguide.ucsd.edu/earthguide/diagrams/absorption/absorption.html

Go to http://www.wiley.com/legacy/college/boyer/0470003790/animations/photosynthesis/photosynthesis.htm

Go through the sections called “Overview” and “Strategy/Players”

                                                                                                                          

    The Light Reactions

• Light Dependent

• “Photo” Division

• Energy Capturing

The Calvin Cycle

• Light Independent

• “Synthesis” Division

• Energy Storage

                                                                                                                                                      

                     

• Occur on thylakoid membranes

• Use 2 Photosystems

• PSI (p700) and PSII (p680)

                                                                                                                                          

                                 

Click image to see a membrane view of the light reactions

• Sunlight strikes p680 boosting electron to excited state

• High energy electrons passed from primary electron acceptor down electron transport system via oxidation-reduction. These reactions power the active transport of H+ from the stroma into the thylakoid space

• H+ diffuse back into stroma through ATP synthetase converting ADP + P into ATP

• Electrons from p680 end up at p700. Hole at p680 filled by oxidation of H2O into O2

• Sunlight hits p700 boosting electron to excited state

• High energy electrons passed from primary electron acceptor down electron transport system via oxidation-reduction.

• High energy electrons transferred by NADP+ reductase to NADP+ to form NADPH

• Hole at p700 filled by electrons from p680

                                                                                                                                       

                            

Click image for link to animated overview of noncyclic photophosphorylation

Sunlight + H2O O2 + ATP + NADPH

ADP, P, and NADP+ from Inorganic Nutrient Pool are raw materials Study the following tutorials:

You control the light reactions!

Biology Project Light RXNs Tutorial

Photosynthesis Light RXNs Interactive

Occurs in the Stroma

Uses ATP and NADPH from Light Rxns

CO2 is Raw Material

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Phase 1: Carbon Fixation

CO2 comes into the stroma of the chloroplast via the stomata of the leaves. 

Rubisco catalyzes the bonding of CO2 to RuBP to create an unstable 6-carbon molecule that instantly splits into two 3-carbon molecules of 3-PGA.

Back to diagram

Phase 2: Reduction

ATP phosphorylates each 3-PGA molecule and creates 1,3-bisphosphoglycerate (1,3 DPGA). 

NADPH reduces 1,3-bisphosphoglycerate which causes the molecule to become glyceraldehyde-3-phosphate (PGAL). NADPH is oxidized by this process and becomes NADP+.

Back to diagram

Phase 3: Regeneration

For every six molecules of PGAL created, five molecules continue on to phase 3 while one leaves to be used for organic compounds.

ATP is once again needed.  However, this time it phosphorylates G3P to regenerate RuBP after some rearrangement.

Back to diagram

Summary of Calvin Cycle

CO2 + ATP + NADPH ADP + NADP+ + PGAL

PGAL is rearranged to produce:

• Glucose for cellular respiration

• Fructose in Fruits

• Sucrose for Transport Throughout Plant

• Starch for Storage Study the following tutorials:

The 3 Phases Animated

Calvin Cycle Tutorial at Biology Project

Photosynthesis Dark RXNs Interactive

Plants fight water loss and dehydration

• Close stoma to prevent water loss

• Closed stoma mean no input of CO2 into leaf

• Light reactions continue to produce O2

Photorespiration

• When O2 concentration increases, rubisco adds O2 to the Calvin Cycle instead of CO2

Photorespiration

• Occurs on bright, hot, dry days when stoma close

• Consumes O2

• Releases CO2

• Unlike cellular respiration, generates no ATP

• Unlike photosynthesis, generates no food

• Actually decrease rate of photosynthetic output

Mechanisms to fight photorespiration: C4 and CAM pathwaysIncorporate CO2 into organic acids first, then release it into the Calvin Cycle

• PEP Carboxylase accepts CO2 in mesophyll cells

• A 4C intermediate carries the CO2 into the bundle-sheath cells

• This maintains a high concentration of CO2 in the bundle sheath to avoid photorespiration