1. Photosynthesis Mini Unit
STEM Biology
Photosynthesis Mini Unit

2. Review: Cellular Respiration
ALL living organisms can do a part of cellular respiration
Breakdown of glucose into energy (ATP) – where most energy is made if oxygen is present!
Cytoplasm and Mitochondria (Matrix and Cristae)
After glucose is present in cells
To create energy for the cell to do work
4 stages….. (did that already)
Who?
What?
Where?
When?
Why?
How?

3. Equation for Cellular Respiration
____________ + _____________  __________ + _________
C6H12O6 + 6O2  6CO2 + 6H20.
What can I add to the end of the equation?
36-38 ATP
Ok so now, what do we know about photosynthesis? Brainstorm on white board.
Equation for Cellular Respiration

4. Who does Photosynthesis?
ALL plants
Algae
Some bacteria
These organisms are also called producers, or autotrophs.

5. What is photosynthesis?
A process that captures light energy from the sun and transforms this light energy into high-energy sugar molecules.
Has 2 stages (details coming later)
What do you think the equation would be for photosynthesis?
This Photo by Unknown Author is licensed under CC BY

6. Equation for Photosynthesis
____________ + ____________  ____________ + ____________
6CO2 + 6H20  C6H12O6 + 6O2
Opposite of cellular respiration (without the ATP added)
What are the reactants?
What are the products?
The arrow is like an equal sign, so notice that each side equals the other side.
Left side of the arrow!
Right side of the arrow!

7. Where does Photosynthesis occur?
Chloroplast!
2 membranes – Electron Transport Chain
Thylakoid – absorbs the light energy from the sun
Stroma – contains the enzymes for the chemical reactions

8. When does photosynthesis occur?
1st stage of photosynthesis MUST take place in the light! This stage is called the light reactions.
2nd stage of photosynthesis does not require light. This stage is called the dark reactions.
This Photo by Unknown Author is licensed under CC BY-SA

9. Why is photosynthesis important?
The glucose made by photosynthesis is used by plant and animal cells
It produces oxygen which helps regulate Earth’s environment
The oxygen is required for aerobic organisms and gets rid of the CO2 from Earth’s atmosphere
Nearly all organisms on Earth depend on photosynthesis
Why is photosynthesis important?

10. How does photosynthesis work?
2 Stages
Light dependent reactions
Dark Reactions (light independent reactions); also called the calvin cycle
ATP is going to be made and used in the process
NADPH is going to be made and used in the process
Very similar to NADH, but has a phosphate group attached
This Photo by Unknown Author is licensed under CC BY

11. Stage 1: Light Dependent Stage
Takes place within and across the membranes of the thylakoids, which are stacked inside the chloroplast.
Main function is to capture the light and transfer the energy
6 steps

12. 6 Steps of Stage 1: Light Dependent
Energy is absorbed from sunlight into the thylakoid.
Water molecules split into oxygen, protons and electrons
Oxygen gets released out into the atmosphere
Protons stay inside the thylakoid
Electrons get the high energy from the sun (transfer of energy)
The protons get pumped across the thylakoid membrane, which causes a buildup of them – form of stored energy. The electrons move down the electron transport chain and energy gets transferred to ATP. Now the electron has low energy.

13. This Photo by Unknown Author is licensed under CC BY-SA-NC

14. 6 Steps of Stage 1: Light Dependent
Energy is absorbed from sunlight again into the thylakoids giving electrons energy again.
NADP+ accepts the high energy electrons and makes NADPH, which is an energy-carrying molecule
Hydrogen ion diffusion – protons diffuse out of the thylakoid through ATP synthase. ATP is made! (just like cellular respiration)

15. This Photo by Unknown Author is licensed under CC BY-SA-NC

16. Summary of Light dependent phase
Required: Water, ADP, NADP+, chlorophyll
Products: Oxygen, ATP, NADPH
So now we have ATP and NADPH energy……now on to the light independent phase!

17. Light independent reactions (Dark Reactions)
Light is NOT required
These reactions can take place anytime the energy of ATP and NADPH are available
Energy is needed for the Calvin Cycle, which will make sugars like glucose!
4 steps

18. Light Independent Reactions (Calvin Cycle) 4 STEPS
Carbon Dioxide is added to a 5C molecule already in the cycle – making a 6C molecule
The 6C molecule splits into 2 3C molecules. ATP and NADPH provide the energy to rearrange them into these 3C molecules.
1 of the 3C molecules leaves the cycle and the other stays. Once there is 2 3C molecules out of the cycle, a 6C molecule of sugar (glucose) is made.
The 3C molecule that stayed in the cycle is transferred back to the original 5C molecule (back in step 1). This transfer requires ATP.

19. This Photo by Unknown Author is licensed under CC BY-SA-NC

20. Summary of Independent Light Reactions (Dark Reactions)
Requires: ATP, NADPH, CO2
Products: Glucose
Summary of Independent Light Reactions (Dark Reactions)