1. Photosynthesis & Cellular Respiration
How plants get Energy

2. Photosynthesis
Photosynthesis - the process in which green plants use the energy of sunlight to convert water and carbon dioxide into carbohydrates and oxygen

3. Photosynthesis There are two main steps in Photosynthesis.
Light reaction
Calvin Cycle

4. The Photosynthesis Equation
Photosynthesis takes place inside the chloroplast.
The Photosynthesis Equation
The equation for photosynthesis is:
6CO2 + 6H2O C6H12O6 + 6O2
carbon dioxide + water sugars + oxygen

5. Inside a Chloroplast
Chloroplasts contain thylakoids—saclike photosynthetic membranes.
Thylakoids are arranged in stacks known as grana. A singular stack is called a granum.
Stroma – space outside of the thylakoids
Granum
Stroma
Single
thylakoid
Chloroplast

6. Inside a Chloroplast
Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters called photosystems, which are the light-collecting units of the chloroplast in the thylakoid membrane.
Photosystems
Chloroplast

7. Light and Pigments photosynthesis requires chlorophyll
pigments - light-absorbing molecules that gather the sun's energy
The main pigment in plants is chlorophyll.
There are two main types of chlorophyll:
chlorophyll a
chlorophyll b

8. Light and Pigments
Chlorophyll does not absorb light in the green region of the spectrum. Green light is reflected by leaves, which is why plants look green.
100 80 60 40 20
Chlorophyll b
Estimated Absorption (%)
Chlorophyll a
Photosynthesis requires light and chlorophyll. In the graph above, notice how chlorophyll a absorbs light mostly in the blue-violet and red regions of the visible spectrum, whereas chlorophyll b absorbs light in the blue and red regions of the visible spectrum.
Wavelength (nm)

9. Light Reaction
With in each Thylakoid there is Photo system 1 and Photo system 2.
Basically these are two light absorbing molecules.
They work at the same time.

10. Light Reaction Sep 1
Light energy forces electrons in the chlorophyll of Photosystem 2 to become excited.
This means that have more energy than usual.

11. Light Reaction Step 2
The electrons leave the chlorophyll molecule of Photo system 2 and are accepted by the primary electron acceptor.
This begins the start of the electron transport chain and activates the Hydrogen pumps.
Hydrogen is pumped into the Thylakoid.

12. Light Reaction
The Hydrogens inside the Thylakoid then flow back out of the Thylakoid through an ATP Synthesizer.
The ATP Synthesizer makes ATPs

13. Light Reaction

14. Light Reaction
At the same time Photosystem 1 gets the electrons passed down the ETC.
These electrons and Hydrogens are donated to NADP (cousin to NAD).

15. Light Reaction

16. Light Reaction SO…. Where did the electrons that were lost come from?
Water!
An enzyme in the Thylakoid breaks two water molecules down into four hydrogen ions (H+), their 4 electrons and O2.

17. Light Reaction

18. Calvin Cycle
Now that the plant has made energy it is going to use that energy to make a simple sugar.
But plants NEED CARBON to make sugar.
Plants get Carbon from CO2

19. Calvin Cycle Step 1 We need three CO2 to get started.
We start by hooking the carbon from each CO2 up to a 5 carbon chain.
This now make a 6 carbon chain.

20. Light Reaction ATP comes in and donates a Phosphate to each chain.
You now have 3 6-C chains with a phosphate at each end.

21. Calvin Cycle Step 2 Each carbon chain breaks in half.
ATP comes in and donates another Phosphate to each chain.
You now have 6 three carbon chains with a phosphate at each end.

22. Calvin Cycle Step 3
The NADPH created in photosynthesis gives a hydrogen to each of the three carbon chains.

23. Calvin Cycle Step 3 Cont.
The three carbon chains now give off a phosphate.
Yes we gained 6 phosphates to lose 6 phosphates. CRAZY!
But this gives the three carbon chains the energy needed to rearrange slightly.

24. Calvin Cycle Step 4
One of the new three carbon chains leaves to become a carbohydrate.
The rest of the 3 carbon chains use 3 ATPs to recombine into the 5 carbon chains.
WE MADE SUGAR AND CELLULOSE!

25. Light- dependent reactions
Inside a Chloroplast
H2O
CO2
Light
NADP+
ADP + P
Light- dependent reactions
Calvin Cycle
Calvin cycle
The process of photosynthesis includes the light-dependent reactions as well as the Calvin cycle.
Chloroplast O2
Sugars

26. Factors Affecting Photosynthesis
Many factors affect the rate of photosynthesis, including:
Water
Temperature
Intensity of light

27. Comparing Photosynthesis and Cellular Respiration
The energy flows in photosynthesis and cellular respiration take place in opposite directions.

28. Comparing Photosynthesis and Cellular Respiration
On a global level, photosynthesis and cellular respiration are also opposites.
Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back.
Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food.