1. Unit 6- Photosynthesis & Cellular Respiration
6a- Photosynthesis

2. First Homework (New Semester)
Bring a leaf to class tomorrow

3. Life Requirements
All organisms need a constant source of energy to survive.
The ultimate source of energy for most life on Earth is the Sun.

4. Trapping the Sun’s Energy
Photosynthesis is the overall process by which solar energy is used to chemically convert water and carbon dioxide into chemical energy stored in simple sugars.
Involves a complex series of chemical reactions in which the product of 1 reaction is a reactant in the next
Biochemical pathway

5. Photosynthesis
The process of photosynthesis is generally represented using a balanced chemical equation. However, this equation does not represent all of the steps that occur.
Sunlight
6CO2 + 6H2O C6H12O6 + 6O2

6. Steps of Photosynthesis
Photosynthesis can be divided into two stages
Light-dependent Reaction
Solar energy is absorbed by chloroplasts and two energy-storing molecules (ATP & NADPH) are produced.
Calvin Cycle (Light-independent reaction)
Simple sugars (glucose) are formed using CO2 & the energy stored in ATP & NADPH
Previously, these reactions were called the light reaction and the dark reaction. While some text still refers to the Calvin Cycle as the dark reaction, most do not because it contributes to the misconception that the Calvin cycle occurs at night.

7. Structure of Chloroplasts
Photosynthesis takes place in the chloroplasts
Each chloroplast is surrounded by a pair of membranes.
Inside the inner membrane is another system of membranes called thylakoids.
Arranged as hollow disks
Connected & layered to form stacks called grana
Surrounding the grana is a solution called the stroma.
Chloroplasts have 3 phospholipid bilayers

8. Where does each step take place?
Light-dependent reactions take place in the membranes of the thylakoid disks
Calvin Cycle takes place in the stroma

9. Review of Light Light from the sun- white light
Can be separated into its component colors by passing the light through a prism
Results in the visible spectrum (ROYGBIV)
When white light strikes an object, its component colors can be reflected, transmitted, or absorbed.
Pigments- compounds that absorb light
Most absorb certain colors more strongly than others, so the light that is reflected no longer appears white.

10. The Role of Chloroplasts and Pigments
The thylakoid membranes contain the pigments that can absorb certain wavelengths of sunlight.
The most important pigment is chlorophyll.
Absorb most wavelengths of light except for green. Green is reflected making the plants appear green.
In the fall, plants reabsorb chlorophyll leaving other pigments that reflect other wavelengths of light – making the leaves appear red, yellow, or orange.
In leaves of plant, chlorophyll’s much more abundant and mask colors of other pigments. In the nonphotosynthetic parts like flowers, the other pigments are visible
During the growing season, chlorophyll is continually being produced and broken down & leaves appear green. As night length increases in the Fall, chlorophyll production slows down & then stops & eventually all the chlorophyll is destroyed.

11. Light-Dependent Reactions
Sunlight strikes the chlorophyll molecules in the thylakoid membrane.
Chlorophyll absorbs the light & the solar energy is used to split water molecules (photolysis)
Results in the release of oxygen (O2) as a waste product.
Allows for the temporary transfer of the solar energy to electrons released by the broken bonds
Electrons are passed down an Electron Transport Chain
Photo- light…..lysis-split
a water molecule is split (photolysis) into protons (H+), electrons, & oxygen.
Electrons sent back to the chlorophyll, H+ left inside thylakoid, & the O2 diffuses out of the chloroplast & leaves the plant through stomata
Photolysis 

12. Light Dependent Reactions
The Electron Transport Chain is a series of proteins in the thylakoid membrane.
As the electrons are transferred from one protein to another, some energy is released.
This energy is used to make ATP & NADPH (electron carrier molecule)
As the electrons are transferred from one protein to another, some energy is released which is used to…
Join H+ and NADP+ (& 2e-) forming NADPH (electron carrier)
Pump hydrogen ions into the center of the thylakoid disk to join ADP and an inorganic phosphate to form ATP (via ATP Synthase)
ATP and NADPH will be used during the Calvin Cycle

13. Light Dependent Reactions

14. Light-dependent Reactions
Solar Energy absorbed by chloroplasts
Oxygen released
ATP Released
Products of Light Reactions (ATP and NADPH) fuel the Calvin Cycle
NADPH released

15. Video https://www.youtube.com/watch?v=joZ1EsA5_NY (3:30)
(7:35-8:20, end of light-dependent)

16. Calvin Cycle
A series of enzyme-assisted chemical reactions that produces 3-carbon sugars
Occurs in the stroma of the chloroplast
Uses the ATP & NADPH that was produced during the light reactions and CO2 from the atmosphere

17. Calvin Cycle
Carbon Fixation:
An enzyme combines CO2 with a 5-carbon molecule called ribulose biphosphate (RuBP).
6-carbon molecule is very unstable, so it immediately splits into two 3-carbon molecules called 3-phosphoglycerate (3-PGA or PGA)
Reduction
Each 3-PGA is converted into another 3-carbon molecule, PGAL (aka G3P) in 2 steps.
1- receive a phosphate group from ATP; 2- receive a proton from NADPH
ADP & NADP+ will be used again in light reaction
PGAL leaves & is used to build glucose (or other carbohydrates).
Regeneration
Remaining PGAL molecules converted back to RuBP by the addition of a phosphate group from ATP. Enter Calvin Cycle again.
Students are not responsible for this information. All they need to understand is that the Calvin Cycle uses the products of the light reaction to produce 3-carbon sugars that will be recycled to keep the cycle going or will be used to produce glucose, other carbs, or other organic molecules

18. The Calvin Cycle Uses Carbon Dioxide from the air
Uses ATP and NADPH from light reactions to build PGAL- a 3-carbon sugar
Uses another ATP to replenish RuBP
Or the 3-carbon sugars can be recycled to keep the Calvin Cycle going.
PGAL= G3P- glyceraldhyde 3-phosphate
The 3-carbon sugars can be used to build a glucose molecule

19. Photosynthesis Equation
Light Energy
6CO2 + 6H2O C6H12O6 + 6O2
chlorophyll
Carbon Dioxide from the air – Used in the Calvin Cycle
Glucose Made in the Calvin Cycle
Oxygen Released during Photolysis in the Light Reactions
Water Split during Photolysis in the Light Reactions
Plants can use this glucose molecule for energy during Cellular Respiration. Plants can also convert this glucose molecule into other organic compounds such as proteins and fats/lipids or other carbohydrates like starch and cellulose

20. Cycle of Photosynthesis

21. 3 Factors that Affect Photosynthesis
Carbon Dioxide (CO2)
Without CO2, the plant would not have one of the raw materials needed for photosynthesis
CO2 is used in the first step of the Calvin Cycle
Temperature
The temperature must be in the appropriate range for the plant in order for photosynthesis to properly occur

22. 3 Factors that Affect Photosynthesis
Intensity of Light
If the intensity of light is lower, the available energy for photosynthesis is lower.
In a greenhouse, if the light source is further away, intensity is lower and less photosynthesis can occur
If light is not available at all, the light-dependent reactions cannot occur (nor can they provide the materials used in the Calvin Cycle)

23. Video https://www.youtube.com/watch?v=joZ1EsA5_NY (3:30)
(8:20, end of light-dependent)