1. Photosynthesis

2. Chloroplast Structure
Photosynthesis occurs in the chloroplasts of plant leaf cells
Chloroplast structure includes
Double membrane
Grana
Look like a stack of coins
Membrane is called the “thylakoid membrane”
Stroma
Fluid surrounding the grana

4. Absorption vs Action
this phenomenon can be demonstrated by an absorption spectrum, which shows chlorophyll’s light absorption vs. wavelength of light, or an action spectrum, which shows the effectiveness of different wavelengths of light at driving photosynthesis

5. Overview
Photosynthesis consists of light-dependant and light-independent reactions
Light-dependent reaction (aka photolysis)
Consists of Photosystems I and II
Occurs in the thylakoid membrane of the grana
Thylakoid membrane contains chlorophyll (pigment that absorbs red and blue light and reflects yellow and green)

6. Overview

7. Light-Dependent
The light-dependent reaction begins with a chlorophyll molecule at the beginning of Photosystem II that has an absorption peak at 680 nm and is referred to as P680
The P680 cholorophyll molecule absorbs a photon of light
As a result, one of it’s electrons becomes excited and moves to a higher energy state

8. Light-Dependent

9. This energized electron is transferred along a series of electron acceptors located in the thylakoid membrane (called the electron transport chain)
As the electron is passed from carrier to carrier the energy released is used to pump hydrogen ions from the stroma to the thylakoid space (inside of the thylakoid)
Hydrogen Ions are created through photolysis
These protons then diffuse back to the stroma down the concentration gradient

10. They are able to cross the thylakoid membrane by traveling through protein channels in ATP Synthase, thus producing ATP
This process is called chemiosmosis (8.2.4)
Once the electron leaves the last carrier in Photosystem II it moves on to replace an electron that is lost from the chlorophyll of Photosystem I after it has been excited by a photon of light
The chlorophyll in Photosystem I is called P700 due to the fact that its peak wavelength of light absorption is 700 nm

11. Once the electron from P700 is excited it is passed down another electron transport chain until it reaches the carrier ferredoxin
Ferredoxin passes the electron to NADP which, when given two electrons, will bind with H+, forming NADPH (reduction)
The electron originally lost from P680 in Photosystem II is replaced by the splitting of water and results in the release of oxygen (two water molecules must be split in order for one molecule of O2)

13. Light independent Rxn Calvin Cycle (C3)
Light-independent Reaction (aka the Calvin Cycle or the C3 cycle)
Occurs in the stroma
Consists of thirteen reactions that are divided up into three phases
CO2 uptake
carbon reduction
RuBP (ribulose biphosphate) regeneration

16. During the C02 reuptake phase a single reaction takes place in which carbon dioxide combines with a phosphorylated five-carbon compound called RuBP
The enzyme that catalyzes the reactions is called Rubisco and may be one of the most abundant proteins in the biosphere
The product of this reaction is an unstable six-carbon intermediate which immediately breaks down into two molecules of glycerate -3-phosphate(3C) with three carbons each (hence the term ‘C3’ cycle)

17. The carbon reduction phases consists of two steps in which the energy and reduction power of ATP and NADPH (both produced in the light-dependent reactions) are used to convert the glycerate -3-phosphate(3C) molecules to G3P(3C)
For every six turns of the cycle (in which 6 carbons have been “fixed” from C02) 12 G3P molecules are created

18. 2 of these 12 G3P molecules are released from the cycle and will combine together to form glucose or fructose
The remaining 10 G3P molecules will go through a complex series of 10 reactions called the RuBP regeneration phase:
their atoms are rearranged and then phosphorylated in order to create 6 molecules of RuBP which can help the cycle to start again

20. C4 and CAM plants
fix CO2 at lower rates than C3 plants
live in conditions in which survival depends on opening stomata less and thus taking in less CO2 (i.e. desert plants that don’t want to lose too much water)
The key component of the C4 pathway is an enzyme called PEP carboxylase that has an extremely high affinity for CO2

21. CAM plants live in extremely dry/hot conditions and therefore fix CO2 at night, then store it until the daytime in which light can be absorbed for photosynthesis

22. Chloroplasts Structure/Function
The chloroplast structure is closely related to its function
Has an intricately folded membrane that provides more surface area for light absorption
These foldings form the thylakoids, which, when stacked upon each other, form grana

23. The thylakoids provide a small space inside for the accumulation of protons to use in ATP production
The fluid in the chloroplast (stroma) has enzymes that are used in the Calvin cycle (aka Rubisco)

24. Photosynthesis Limiting factors in photosynthesis
Limiting factors are conditions that are essential for the life of the plant
Can affect how well the plant can photosynthesize and thus how well it survives
Many plants prefer a particular amount of light intensity

25. Temperatures must also be within a certain range for different plants to survive
Various plants have different requirements in terms of how much carbon dioxide they need (think about C4 plants vs. C3 plants)