1. AP Bio Photosynthesis Review
Wolfoline and Angelica

2. Introduction 6 CO2 + 6 H2O C6H12O6 + 6 O2 Two Stages of Photosynthesis
1.The Light Reactions or Light-Dependent Reactions
2.The Calvin Cycle or Dark Reactions or Light- Independent Reactions

3. Where Photosynthesis takes place
Most photosynthesis occurs in leaves, and most of the energy used by life on Earth comes from the sun

4. Energy Flow
Chloroplasts are found in mesophyll cells forming the tissues in the leaf.
Powered by light, the green parts of plants produce organic compounds and O2 from CO2 and H2O.

5. 2 stages of photosynthesis
The light reactions convert solar energy to chemical energy
The Calvin cycle uses energy from the light reactions to incorporate CO2 from the atmosphere into sugar.

6. Wavelengths
Light travels in rhythmic waves, and wavelengths of electromagnetic radiation range in sizes, creating the electromagnetic spectrum.
Visible light is between 380 to 750 nm.
Photons (a particle of light)
Different pigments absorb photons of different wavelengths, and those not absorbed disappear, creating the green look on plants bc chlorophyll (dominant pigment) absorbs red and blue light, reflecting green light.
Chlorophyll A
Chlorophyll B
Carotenoids
Xanthophyll
Carotenes

7. Light Reactions
Light energy absorbed by chlorophyll in the thylakoids drives the transfer of electrons and hydrogen from water to NADP+, forming NADPH.
Light energy is converted to chemical energy in the forms of NADPH and ATP
NADPH, an electron acceptor, provides reducing power via energized electrons to the Calvin Cycle. Water is split, and O2 is produced as a byproduct.
The light reaction generates ATP through chemiosmosis in the process of photophosphorylation.

8. Photosystems
A photosystem is a cluster of pigment molecules bound to proteins, along with a primary electron acceptor.
2 photosystems are involved:
Photosystem II (P680)
Absorbs light best at a wavelength of 680nm
Photosystem I (P700)
Absorbs light best at a wavelength of 700nm

9. Noncyclic photophosphorylation
During Noncyclic photophosphorylation, electrons enter two electron transport chains. The process begins in PSII and proceeds through the steps.
Photosystem II absorbs the energy in a photon , exciting an electron to a higher energy level.
PSII is now 1 electron SHORT of what it needs.
This electron is replaced by photolysis – the splitting of water using light.
O2is released as a byproduct.
Electron Transport Chain- Electrons from P680 pass along the ETC to the P700 (PSI). The flow of electrons is exergonic and provides energy to produce ATP by chemiosmosis.

10. 4. Chemiosmosis- ATP is formed during the light reactions of photosynthesis. Protons released from water are pumped by thylakoid membrane into the thylakoid space (lumen). ATP forms as protons diffuse down the gradient from thylakoid space through ATP synthase channels, into stoma.
5. NADP becomes reduced when it picks up the two protons released from water in P680. NADPH forms carrying hydrogen to the Calvin cycle to make sugar.
6. Photosystem I (P700)- Energy is absorbed in PI. Electrons from chlorophyll a become energized and are captured by a primary electron acceptor. Electrons are however replaced with electrons from photosystem II, not water. This ETC produces NADPH, not ATP.

13. Cyclic photophosphorylation
•Cyclic phosphorylation is a more ancient biochemical pathway.Most photosynthetic bacteria & all photosynthetic eukaryotes use cyclic phosphorylation.
•Cyclic electron flow produces ATP, but does not produce NADPH.
–Only photosystem I is used
–Electrons are “recycled”
–Water is not split
BC the calvin cycle requires a lot of ATP, sometimes chloroplasts run low on ATP and when this occurs cyclic p.begins.
Cyclic electron flow takes photoexcited electrons on a short-circuit pathway. Electrons travel from P680 etp to P700, to a primary electron acceptor, and back to the cytochrome complex in P680 etp.

14. Calvin Cycle The Calvin Cycle occurs in the stroma of chloroplasts.
The Calvin cycle is the main component of light-independent reactions.It is a cyclical process that process the 3-carbon sugar PGAL.
Carbon enters the stomata of a leaf as COx and becomes fixed into PGAL.
The process that occurs in the Calvin cycle is called carbon fixation. It is a reduction reaction (carbon gaining protons and electrons).
The Calvin Cycle occurs in the stroma of chloroplasts.

15. Step 1: Carbon Fixation
3 molecules of CO2 (from the atmosphere) are joined to 3 molecules of RuBP (a 5-carbon sugar) by Rubisco (an enzyme also known as RuBP carboxylase)
Step 2: Reduction
The three 6-carbon molecules (very unstable) split in half, forming six 3-carbon molecules.
These molecules are then reduced by gaining electrons from NADPH. ATP is required.
There are now six 3-carbon molecules, which are known as G3P or PGAL.
Since the Calvin Cycle started with 15 carbons (three 5-carbon molecules) and there are now 18 carbons, we have a net gain of 3 carbons.

16. Step 3: Regeneration of RuBP
Since this is the Calvin Cycle, we must end up back at the beginning.
The remaining 5 G3P molecules (3-carbons each!) get rearranged (using ATP) to form 3 RuBP molecules (5-carbons each).
In summary, CO2 enters the cycle and attaches
to a 5 carbon sugar, RuBP, forming a 6 carbon
sugar molecule. The 6 carbon molecule is unstable
And breaks down into two 3 carbon molecules of
3-phosphoglycerate (3-PGA). The enzyme that
catalyzes this first step is rubisco.

18. Environmental factors
The rate of photosynthesis can vary, based on enviro. conditions.
•Light intensity
As light intensity increases, so too does the rate of photosynthesis.
•Temperature
The effect of temperature on the rate of photosynthesis is linked to the action of enzymes.
As the temperature increases up to a certain point, the rate of photosynthesis increases.
•Oxygen concentration
As the concentration of oxygen increases, the rate of photosynthesis decreases.
This occurs due to the phenomenon of photorespiration.
*Photorespiration occurs when Rubisco (RuBP carboxylase) joins oxygen to RuBP in the first step of the Calvin Cycle rather than carbon dioxide.
•This occurs due to increased excitation of electrons in the photosystems.
•However, the photosystems will eventually become saturated.
Above this limiting level, no further increase in photosynthetic rate will occur
More CO2 photosynthesis occurs more o2 photorespiration occurs

19. C3, C4, and Cam plants
C3 plants, which are “normal” plants, perform the light reactions and the Calvin Cycle in the mesophyll cells of the leaves. Stomata are open during the day. RUBISCO, the enzyme involved in photosynthesis, is also the enzyme involved in the uptake of CO2.
C4 plants and CAM plants modify the process of C3 photosynthesis to prevent photorespiration.
CAM plants open stomata at night to bring in
CO2, then they fix it to one of a few organic acids. These molecules are stored in
vacuoles until day time when the stomata close and now the Calvin cycle can begin as
the previously made organic acids now decarboxylate and release the CO2 to keep the
relative concentration high for rubisco. C4 and CAM are similar, but CAM does
everything in the mesophyll…NO bundle sheaths are involved. Examples:
CAM is common in cacti and other succulent plants as well as pineapples and
other bromeliads

20. Review

21. Kahoot