1. Photosynthesis
AP Biology
Unit 4

2. Vocabulary Review What is an autotroph? What is a heterotroph?
Make their own energy
What is a heterotroph?
Aren’t able to make own energy– have to get it from another source

3. Photosynthetic Organisms
Photosynthesis is one way to make your own energy
Who does it?
Plants, algae, some other protists, some prokaryotes (ex. cyanobacteria)

4. Location of Photosynthesis
Photosynthesis occurs in the chloroplasts
Organelles that contain the pigment chlorophyll and other pigments
Openings in the leaf (stomata) allow CO2 (reactant) to enter and O2 (product) to leave

5. Equation for Photosynthesis
6 CO H2O + ENERGY  C6H12O O2
In terms of reactants and products, it is the reverse of cellular respiration, but process is different.

6. Stages of Photosynthesis
Light Reactions
Captures light energy to produce ATP and NADPH
Calvin Cycle (“Dark” Reactions)
Uses ATP and NADPH to “fix” carbon into a carbohydrate
“fix” means to incorporate the carbon into a compound

7. Light Reactions
Main point = convert sunlight energy into chemical energy (ATP and NADPH)
Sunlight can be divided into different wavelengths of light– only some are useful in photosynthesis

8. Light Reactions
Photosynthetic pigments in the chloroplast absorb different wavelengths
Chlorophyll a
Chlorophyll b
Carotenoids

9. Question… Why are most plants green?
The chlorophyll and carotenoid molecules absorb the blue-violet and red light and use it to perform photosynthesis
They reflect green light – colors we see are the reflected wavelengths.

10. Light Reactions: Photosystems
Photosystems are the complex of pigments that receives the sunlight to begin the process
Photosystems absorb energy to excite an electron in chlorophyll
There are 2 different photosystems in chlorophyll – I and II.

11. Light Reactions: Noncyclic Flow
Step 1: Light excites electrons in photosystems I and II
Step 2: Excited electrons are passed down an electron transport chain – generates ATP and NADPH

12. Noncyclic Flow
Excited electron from Photosystem II fills the space left in Photosystem I
Water is split (photolysis) to provide an electron to fill the space left in Photosystem II

13. Cyclic Electron Flow
Under certain circumstances, the excited electrons will only flow through Photosystem I (not II)

14. Cyclic Electron Flow Generates ATP Doesn’t generate NADPH
Runs because the Calvin Cycle needs more ATP than NADPH
May shift from noncyclic to cyclic flow when NADPH levels are high

15. Electron Transport Chain
very similar to cellular respiration
An H+ concentration gradient across the thylakoid membrane drives ATP synthesis

16. Calvin Cycle
Also called the Dark Reactions, Non-light Dependent Reactions, or the Calvin Benson Cycle
Uses the ATP and NADPH produced in the light reactions to produce glucose using CO2

17. Calvin Cycle: Rubisco
Rubisco is the enzyme that first “traps” CO2 into the cycle
Through a series of reactions, CO2 is used to eventually make glucose

18. Calvin Cycle
CO2 only contributes 1 carbon  6 “turns” of the calvin cycle are needed to produce one glucose.
RuBP also has to be regenerated so that cycle can continue

19. The O2 released during photosynthesis comes from
NADPH
RuBP (RuDP)
C6H12O6 15

20. Carbohydrate-synthesizing reactions of photosynthesis directly require
Light
Products of the light reactions
Darkness
O2 and H2O
Chlorophyll and CO2 15

21. The end products of the light-dependent reactions of photosynthesis are15
ADP, H2O, NADPH
ADP, PGAL, RuBP (RuDP)
ATP, CO2, H2O
ATP, NADPH, O2
CO2, H+, PGAL