1. 2/27 Daily Catalyst Pg. 85 The Dark Reaction
1. Grab a baggie from the front of the classroom and with a partner, begin matching the pieces to one another on photosynthesis.
2. Review the light reaction with your partner.

2. 2/27 Class Business Pg. 85 The Dark Reaction
Quiz #21 TODAY
Study log due TODAY
Next week- enzymes and energy test!

3. 2/27 Agenda Pg. 85 The Dark Reaction
Daily Catalyst
Class Business
Finish dark reaction notes
Review
Quiz #21
Trade and grade
Timed 10
Homework: workbook page 46-48, questions 1-5 and read

4. Photosynthesis Part II:
The Dark Reaction
Pg. 85 The Dark Reaction

5. Phase 2: The Calvin Cycle
Key Point #1: The Calvin Cycle occurs in the stroma of chloroplasts.
Light is NOT needed (dark reaction). It doesn’t occur in the dark.
In the Calvin Cycle, ATP (from the light reactions) and CO2 (from the atmosphere) are used to produce organic compounds (like glucose).

6. Phase 2: The Calvin Cycle
Key point #2: The Calvin Cycle involves the process of carbon fixation.
This is the process of merging carbon from a non-organic compound (ie. CO2) into an organic compound (ie. carbs).
CARBON FIXATION

7. Phase 2: The Calvin Cycle Key Point #3: The Calvin Cycle
Step 1: Carbon Fixation
3 molecules of CO2 (from the atmosphere) are joined to 3 molecules of RuBP (sugar) by Rubisco (an enzyme) C C
This forms 3 molecules with 6 carbons (for a total of 18 carbons!)
1. Discuss with a partner how this is CF.
- Only the carbons are shown in this diagram for clarity, though oxygen and hydrogen are also present. Also, the carbon atoms shown in red and those shown in black are identical, but are color-coded to show where they come from (red are CO2 from the atmosphere, black are the carbons in RuBP).
Rubisco C C C C
3 carbon dioxide molecules
3 RuBP molecules

8. Phase 2: The Calvin Cycle
Where did the NADPH and ATP come from to do this?
Step 2: Reduction
The three, 6-carbon molecules (very unstable) split in half, forming six 3-carbon molecules.
These molecules are then reduced by gaining electrons from NADPH.
ATP is required for this molecular rearranging
ATP
- Emphasize to students that the NADPH and ATP required to perform these reactions as part of the Calvin Cycle were produced during the light reactions.
ADP P C C C C C C C C
NADPH C
NADP+

9. Phase 2: The Calvin Cycle
Where did these 3 extra carbons come from?
Step 3: There are now six 3-carbon molecules, which are known as G3P or PGAL.
Since the Calvin Cycle started with 15 carbons (three 5-carbon molecules) and there are now 18 carbons, we have a net gain of 3 carbons.
One of these “extra” 3-carbon G3P/PGAL molecules will exit the cycle and be used to form ½ a glucose molecule.
Emphasize to students that these 3 extra carbons came from the carbon dioxide, which was obtained through the stomata from the atmosphere; these 3 additional carbons are denoted in red.
Remember to emphasize that this is the Calvin Cycle; we end up where we began. So, since we started with 15 carbons, we will also return to 15 carbons. C C C C C C

10. Phase 2: The Calvin Cycle Key Point #3: The Calvin Cycle
Step 1: Carbon Fixation
3 molecules of CO2 (from the atmosphere) are joined to 3 molecules of RuBP (sugar) by Rubisco (an enzyme) C C
This forms 3 molecules with 6 carbons (for a total of 18 carbons!)
1. Discuss with a partner how this is CF.
- Only the carbons are shown in this diagram for clarity, though oxygen and hydrogen are also present. Also, the carbon atoms shown in red and those shown in black are identical, but are color-coded to show where they come from (red are CO2 from the atmosphere, black are the carbons in RuBP).
Rubisco C C C C
3 carbon dioxide molecules
3 RuBP molecules

11. Phase 2: The Calvin Cycle
The Calvin Cycle “turns” 6 times to make glucose, those 2 molecules of G3P (a 3-carbon carbohydrate) will combine to form 1 molecule of glucose (a 6-carbon carbohydrate molecule).
- We say that the Calvin Cycle turns twice to make one molecule of glucose (6-carbons), but really it turns 6 times; each entering carbon dioxide molecule represents one “turn” of the cycle, and 6 carbon dioxide molecules must be incorporated into organic compounds in order for one 6-carbon glucose molecule to be produced. This PowerPoint (along with many textbooks) shows 3 carbon dioxide molecules entering together for clarity (it’s hard to show 1/3 of a G3P molecule as the product of each turn of the cycle).
- Glucose is what we usually think of as being the major product of photosynthesis; however, G3P (also known as PGAL) is the real product, and though it is often used to make glucose it can also be used as a carbon skeleton to form other organic molecules. C C C C
G3P
(from 3 turns of the Calvin Cycle)
G3P
(from 3 turns of the Calvin Cycle)
glucose

12. Phase 2: The Calvin Cycle
Where does the ATP come from to do this?
Step 4: Regeneration of RuBP
Since this is the Calvin Cycle, we must end up back at the beginning.
The remaining 5 molecules (3-carbons each!) get rearranged (using ATP) to form 3 RuBP molecules (5-carbons each).
Emphasize to students that the other G3P molecule has left the cycle and was used to form glucose (or other organic compounds).
The ATP required to do this rearranging comes from the ATP generated during the light reactions. C C C C C C C
ATP C
ADP
5 G3P molecules Total: 15 carbons
3 RuBP molecules Total: 15 carbons P

13. Phase 2: The Calvin Cycle Key Point #3: The Calvin Cycle
Step 1: Carbon Fixation
3 molecules of CO2 (from the atmosphere) are joined to 3 molecules of RuBP (sugar) by Rubisco (an enzyme) C C
This forms 3 molecules with 6 carbons (for a total of 18 carbons!)
1. Discuss with a partner how this is CF.
- Only the carbons are shown in this diagram for clarity, though oxygen and hydrogen are also present. Also, the carbon atoms shown in red and those shown in black are identical, but are color-coded to show where they come from (red are CO2 from the atmosphere, black are the carbons in RuBP).
Rubisco C C C C
3 carbon dioxide molecules
3 RuBP molecules

14. Phase 2: The Calvin Cycle
CO2
Rubisco
ATP
RuBP
NADPH
- This simple schematic diagram gives a basic overview of what occurs during the Calvin Cycle. Carbon dioxide enters the cycle from the atmosphere and is joined to RuBP by Rubisco. NADPH and ATP are used to “turn” the cycle, and organic compounds (such as G3P/PGAL) are produced.
NADP+
ADP P
ORGANIC COMPOUND

15. Phase 2: The Calvin Cycle
- Though the AP curriculum framework very clearly states that students do not need to memorize the steps in the Calvin cycle, the structure of the molecules and the names of the enzymes involved (except for ATP synthase), some students may find this diagram helpful in understanding the cyclical nature of the Calvin cycle.

16. Phase 2: The Calvin Cycle
Quick recap:
In the Calvin Cycle, energy and electrons from the Light Reactions (in the form of ATP and NADPH) and carbon dioxide from the atmosphere are used to produce organic compounds.
The Calvin Cycle occurs in the stroma inside the chloroplasts (inside the cells…).
Carbon dioxide, ATP, and NADPH are required (reactants).
Organic compounds (G3P) are produced (products).

17. Photosynthesis: A Recap
So, as a broad overview of photosynthesis,
The Light Reactions (Phase 1) capture the energy in sunlight and convert it to chemical energy in the form of ATP and NADPH through the use of photosystems, electron transport chains, and chemiosmosis.
The Calvin Cycle (Phase 2) uses the energy transformed by the light reactions along with carbon dioxide to produce organic compounds.

18. Photosynthesis: A Recap
Based on this equation, how could the rate of photosynthesis be measured?
The photosynthetic equation:
Provides the carbon to produce organic compounds during the Calvin Cycle
The organic compound ultimately produced during the Calvin Cycle
light
6 H2O
6 CO2
6 O2
C6H12O6
Emphasize to students the importance of understanding how and when each component of the photosynthetic equation is used; this is much more valuable (and less intimidating!) than simply having them memorize the equation!
Most realistically, the rate of photosynthesis could be measured by using the:
Decrease in environmental CO2 (in a closed system)
Increase in environmental O2 (in a closed system)
Increase in glucose (perhaps measured using radioactive carbon)
Split during the light reactions to replace electrons lost from Photosystem II
Produced as a byproduct of the splitting of water during the light reactions
Excites electrons during the light reactions

19. Class Practice

20. Review
Directions: With your partner, review the light and dark reaction of photosynthesis.
Time: 10 minutes
Noise: 1 (with a partner)

21. Partners 1 2 3 4 5 6 7 8 John Kiandria Annie Bristin Gianni Daniel
Yennifer
Teresa
Kordell
Erica
Quinshelle
Tiana
Taylor
Tiffany
Daquine
Travia

22. Quiz #21
Directions: Silently and independently complete the quiz. No notes or books may be used. Turn your quiz into the basket when you are finished.
Time: 15 minutes
Noise: 0 (SILENCE)

23. James, Joe, and Paul
Complete the essay question on a lined sheet of paper and turn it into the basket.
1. Matter continuously cycles through an ecosystem. A simplified carbon cycle is depicted below. (a) Identify the key metabolic process for step I and the key metabolic process for step II, and briefly explain how each process promotes movement of carbon through the cycle. For each process, your explanation should focus on the role of energy in the movement of carbon. (b) Identify an organism that carries out both processes.

24. James, Joe, and Paul
Complete the essay question on a lined sheet of paper and turn it into the basket.