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Photosynthesis: Just the Notes

Turning Light into Life


What is Photosynthesis?

Autotrophs convert Sunlight Chemical Energy


Plants  provide:

Chemical energy on which all life depends

Oxygen plants created our atmosphere

Materials shelter, clothing, medicine

Food for (almost) all other life forms    


CO2 + H2O C6H12O6 + O2

       Materials Required for Photosynthesis:

        Sunlight provides energy

        Carbon Dioxide provides carbon

        Water provides electrons

        Oxygen waste product after electrons removed from water

        & enzymes to put everything together!

Where does photosynthesis take place?

Leaf Structures

      Cuticle & epidermis protect plant

      Stomates allow gases in and out

      Veins in leaf transport water, nutrients

    Xylem - water & minerals up from roots

    Phloem - food from leaves to plant

Leaf Structures

      Mesophyll = middle leaf
      Palisade layer is where most photosynthesis takes place
      Cells have many chloroplasts
      Spongy mesophyll allows gases to circulate



n    Link:  Narrate this movie!


Photosynthesis: The Process

2 Phases

 Organelle:  Chloroplasts

Input: Light, Water, CO2

Output: Sugar, O2



Phase 1: The Light Reactions

Purpose convert light energy from the sun to chemical energy (ATP)


Requires:  Light


Electron carriers (NADP+)






O2 as waste

Electron-rich carriers


Different Colors of Light :  Different Energy for Reactions


Pigments and Color

Pigments - molecules that absorb some colors of light and reflect other colors of light

The color you see is the color that is reflected.


Chlorophyll a

Chlorophyll a absorbs blue & red light

Chlorophyll a reflects green/yellow light

Thats why leaves look green!


Clusters of chlorophyll form photocenters in chloroplasts that absorb light energy


Link:  Light Reactions - the Basics



1.  Chlorophyll absorbs light energy from the sun Energy excites electrons in chlorophyll to high energy state electrons bounce out of photosystem


2.  High energy electrons are passed down electron transport chain ATP; the energy is used to make ATP (chemiosmosis)


3.  Electrons are energized again and passed to an electron carrier (NADP+)


Its a 7-Ticket Ride for the electrons!


Electrons excited in step 1 are replaced by electrons from water:

2 H2O 4 H+    4 e-     O2



Products of the Light Reactions


Light Energy excites e-

H2O donates e-

NADP+  carries e-


ATP - Energy for reactions

O2 - waste product

NADPH - provides electrons for CO2 sugar


Links to helpful animations:

summary leaf to NADPH and ATP

Light reactions in 4 stages

Animation of photosystems II and I

A close up of ATP synthase



Phase 2: The Calvin Cycle


Products of Phase 1 are used in Phase 2

ATP  Energy

NADPH e-(electrons)


Stage 2:  Calvin Cycle

Purpose: M
ake sugar from carbon dioxide

Location: Stroma of chloroplast



Electrons (NADPH)*




Produces Glucose



Link to Calvin cycle animation


Calvin Cycle

CO2 enters cycle by becoming attached to a 5-Carbon ribulose-bi-phosphate (RuBP)

6-Carbon molecule (unstable)

2  3-Carbon molecules


Calvin Cycle

Energy provided by (ATP ADP)

Electrons from NADPH used

3-Carbon compound leaves Calvin cycle

2     3-Carbon groups combine to  become glucose

remaining 3-Carbon groups continue through cycle to regenerate starting 5-Carbon RuBP

6 CO2 to produce 1 glucose



Important molecules are recycled



5-Carbon RuBP recycles

Photosynthesis Summary










Show your appreciation for
a green plant today!

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