1. Process of Photosynthesis

2. Objectives Explain why almost all organisms depend on photosynthesis
Describe what happens during the light- dependent reactions
Describe what happens during the light- independent reactions
Distinguish between C3, C4 and CAM plants
Identify factors that affect the rate at which photosynthesis occurs

4. THE LIGHT-DEPENDENT REACTIONS: An Overview
Takes place inside of the thylakoids
Chlorophyll traps the light energy
Makes NADPH and ATP
which get used in the Calvin cycle
Splits water and gives off oxygen
Oxygen (O2) is a waste product

5. Photosystems Are clusters of chlorophyll and proteins
They are surrounded by accessory pigments, which are essential to the light- dependent reactions
Photosystems absorb sunlight and generate high-energy electrons that are then passed to a series of electron carriers embedded in the thylakoid membrane

6. Steps of the Light-Dependent Reactions
Light energy excites electrons in chlorophyll a molecules of photosystem II
The electrons are shot out of photosystem II down the electron transport chain
Protons are moved into the thylakoids as a result of the energy loss

7. Steps of the Light-Dependent Reactions
Photosystem I then absorbs light and shoots out electrons. At the same time, water is split into protons, electrons & oxygen.
The released electrons then change NADP+ into NADPH which is used in the Calvin Cycle
ATP is synthesized when protons are pumped through ATP synthase from inside the thylakoid to the stroma

8. Splitting of Water

9. LIGHT REACTIONS

10. LIGHT REACTIONS Chemiosmosis: The synthesis of ATP Photosystem I
Photosystem II
Chemiosmosis:
The synthesis of ATP

11. The Light-Independent Reactions
AKA the Calvin Cycle
Is a series of enzyme-assisted chemical reactions that produces a three-carbon sugar from carbon dioxide
It was discovered by Melvin Calvin, an American biochemist.
Carbon atoms from CO2 are “fixed” into organic compounds in a process known as carbon fixation
It is the most common pathway for carbon fixation!

12. The Light-Independent Reactions Continued
Uses ATP and NADPH from the light reactions
It requires three CO2 molecules and occurs in the stroma of the chloroplast
It makes glucose
Also known as the C3 pathway, dark reactions & the Calvin-Benson cycle reactions

13. Steps of the Calvin Cycle
An enzyme combines CO2, from the stroma, with a 5-carbon molecule called ribulose bisphosphate (RuBP) forming an unstable 6- carbon molecule
This unstable 6-carbon molecule immediately breaks down into 2 three-carbon molecules known as 3-phosphoglycerate (3-PGA)
Then the 3-PGA molecules are converted into another 3-carbon molecule called glyceraldehyde 3-phosphate (G3P) while using 6 ATPs and 6 NADPHs for energy

14. Steps of the Calvin Cycle
One of the G3P molecules leaves the Calvin cycle and is used to make carbohydrates
The remaining G3P molecule is converted back into RuBP using 3 more ATPs
RuBP molecules then enter the Calvin cycle again

15. Light-Independent Reactions

17. Photosynthesis Equation
Made in the light reactions
Used in the Calvin cycle
Light Energy
6 CO2
C6H12O6
6 O2
6 H2O
Glucose
Oxygen
Carbon Dioxide
Water
Made in the Calvin cycle
Used in the light reactions

18. Alternative Pathways
Are necessary for plants that live in hot, dry climates where water is easily evaporated from the stomata of leaves
Stomata are pores located underneath plant leaves through which O2 & CO2 enter and leave

19. C4 Pathway Enables certain plants to fix CO2 into 4- carbon compounds
During the hottest part of the day, C4 plants have their stomata partially closed
They use an enzyme to fix CO2 into a 4-carbon compounds even when CO2 levels are low
Examples: corn, sugar cane, & crab grass

20. CAM Pathway Cactuses, pineapples, & jade plants use this pathway
CAM is the abbreviation for ___________________________
These plants open their stomata at night and close them during the day
CAM plants take in CO2 at night and fix it into several organic compounds
Then during the day, CAM plants run the Calvin cycle

21. Factors that Affect Photosynthesis
___________: as light intensity increases the rate of the photosynthesis increases
________________: an increased level of CO2 also increases the rate of photosynthesis
___________: increases photosynthesis in a certain range

22. Summary of Photosynthesis
Happens in ________ stages
The light reactions happen in the ____________ membrane
The Calvin cycle happens in the ________
The light reactions use _______, & ________ and produce _________, __________, & ____________.
The Calvin cycle uses _________, _________, & _________ and produces ________.

23. Concept Map Photosynthesis includes use take place in takes place in
Light
reactions
Calvin cycle
use
take place in
takes place in
uses
Thylakoid
membranes
Stroma
NADPH
ATP
Light energy
from sun of
to produce
to produce
Glucose
ATP
NADPH O2
Chloroplasts

24. WHAT HAPPENS TO THE GLUCOSE?
BUT HOW?