Major Concepts to Review for AP Biology



6 CO2 + 12 H20 + light -> C6H12O6 + 6 O2 + 6 H20

This formula does not show important details outlined below

LIGHT reactions
produce - ATP and NADPH2+
require - Visible light except green light
are - endergonic
have 2 photosystems
occur on thylakoid membranes in chloroplast


Photosystem II splits water to get H+ and e- by product is O2
is noncyclic
must be coupled to Photosystem I by mobile carrier called PC
Pumps H+ to make ATP
ends by reducing NADP to NADPH2+
uses Photosystem I to make NADPH2

Photosystem I if uncoupled from pII is cyclic and can only
Pump H+ to make ATP

Both Photosystem I and Photosystem II are electron transport systems and both use chlorophyll to capture light energy


Chemiosmotic Phosphorylation

H+ gradient is used to convert ADP to ATP

Uses CF0 and CF1 complex, an ATP synthase that uses rotary motion produced as H+ flows through the complex

The DARK Reactions or The Calvin Cycle

Uses ATP and NADPH from light reactions to fix carbon dioxide and add hydrogen (reduction reaction to from various carbohydrates including glucose)

Rubisco (carboxylase enzyme) combines CO2 to 5 -Carbon sugar (RuBP) forming an unstable 6-carbon intermediate. 2PGALs result.

6 turns of the Calvin Cycle = 1 glucose (glucose pathway)

or regeneration pathway results in more RuBP (ribulose bisphosphate)

C4 Plants

In Photorespiration Rubisco uses O2 instead of CO2 which is a problem for most plants with only Rubisco

C4 and CAM plants use PEP carboxylase to fix CO2 to be used when conditions get hot and humid (C4) or hot and dry (CAM)


Stroma - non-membranous region within the chloroplast is the site of the Calvin Cycle

Grana are stacks of thylakoid membranes where the light reactions take place. They contain the following molecular complexes

Photosystems I and II for trapping light. Chlorophyll is oxidized and water is split

Electron transport chains. Excited electron's energy is used to pump hydrogen ions. The final electron acceptor is NADPH2

Proton Pump - moves hydrogen ions into the thylakoid interior to create a chemiosmotic proton gradient

CF0 CF1 complex - taps into the potential energy of the proton gradient and converts ADP into ATP.

Lumen of the thylakoid membranes stores hydrogen ions

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