1. Agenda 2/4 Light Reactions Review LR children’s books
Calvin Cycle Notes
Children’s Book Pt 2
Homework: Calvin cycle video and notes, Finish Calvin Cycle book
Turn in: Video Notes, Textbook Notes

2. Who, What, When, Where???
As your warm up identify the main players in the light dependent reactions of photosynthesis:
Example:
Who- ATP
What- Energy needed for the Calvin Cycle
When- After ETC in light dependent reactions
Where- Thylakoid membrane in ATP synthase protein
Do this for ATP, Light, Oxygen, NADPH and Water

3. Photosynthesis Part II:
The Calvin Cycle

4. Photosynthesis: An Overview
The net overall equation for photosynthesis is:
Photosynthesis occurs in 2 “stages”:
The Light Reactions (or Light-Dependent Reactions)
The Calvin Cycle (or Calvin-Benson Cycle or Dark Reactions or Light-Independent Reactions)
6 CO2 + 6 H2O C6H12O6 + 6 O2
light
Photosynthesis is an endergonic reaction because it requires an input of energy to occur; that energy comes in the form of light.
This is a review from the previous PowerPoint, to activate students’ prior knowledge.
Is photosynthesis an ENDERGONIC or EXERGONIC reaction?

5. Photosynthesis: An Overview
To follow the energy in photosynthesis,
light
Light
Reactions
Calvin
Cycle
Organic compounds (carbs)
ATP
NADPH
light
thylakoids
stroma
It cannot be overemphasized that energy is not MADE, but is instead transformed through the processes of photosynthesis and cellular respiration. Each of the “boxes” (light/ATP & NADPH/organic compounds) contains energy, but in a different form. Photosynthesis is a process that converts energy from an “un-usable form” (light) into a “usable form” (organic compounds), and requires an intermediate step (ATP/NADPH).
This is a review from the previous PowerPoint, to activate students’ prior knowledge.

6. Phase 2: The Calvin Cycle
In the Calvin Cycle, chemical energy (from the light reactions) and CO2 (from the atmosphere) are used to produce organic compounds (like glucose).
The Calvin Cycle occurs in the stroma of chloroplasts.

7. Phase 2: The Calvin Cycle
The Calvin Cycle involves the process of carbon fixation.
This is the process of assimilating carbon from a non-organic compound (ie. CO2) and incorporating it into an organic compound (ie. carbohydrates).
CARBON FIXATION

8. Phase 2: The Calvin Cycle
Step 1: Carbon Fixation
CO2 (from the atmosphere) are joined to of RuBP (a 5-carbon sugar) by Rubisco C C
- 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

9. Phase 2: The Calvin Cycle
Step 2: Reduction
The 6-carbon molecules (very unstable) split in half, forming 3-carbon molecules.
These molecules are then reduced by gaining electrons from NADPH.
ATP is required for this molecular rearranging
Where did the NADPH and ATP come from to do this?
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+

10. Phase 2: The Calvin Cycle
Where did these 3 extra carbons come from?
There are now 3-carbon molecules, which are known as G3P or PGAL.
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

11. Phase 2: The Calvin Cycle
Some of the PGAL or G3P can combine to form glucose or other organic molecules
- 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
Step 3: Regeneration of RuBP
Since this is the Calvin Cycle, we must end up back at the beginning.
The remaining G3P/PGAL molecules get rearranged (using ATP) to form RuBP molecules
Where does the ATP come from to do this?
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
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

14. 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.

15. Simplified Steps
1. Carbon dioxide combines with RuBP with assistance by an enzyme called rubisco
2. That new molecule is very unstable and will split in half to form G3P/PGAL
This uses NADPH and ATP
3. Some of the G3P/PGAL will combine to form organic compounds
4. Some of the G3P/PGAL will combine to recreate RuBP (Remember it is a cycle!)
This also needs ATP

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. Photosynthesis: A Recap
Photosynthesis Animation
(click on “Animation” after clicking the link)
- Online animation of the entire process of photosynthesis, including both the light reactions & the Calvin Cycle
- Animation url: