Popeye knew what he was doing! Photosynthesis & Cellular Respiration

Popeye knew what he was doing!

Photosynthesis & Cellular Respiration

Today’s reference:

Sec 5.2

Where did the inspiration for solar-powered calculators, cars, and heating systems come from?

Photosynthetic plants, which can convert solar energy into another form of energy, was the inspiration for solar-powered technology! Let’s see how plants do that at the cellular level.



Photosynthesis – General Overview There are two steps involved in photosynthesis:

1. Light-Dependent Reaction

• Occurring on the thylakoid membrane of the chloroplast, this reaction converts solar energy into ATP and NADPH (a molecule with high reducing power).

2. Light-Independent Reaction

• Occurring in the gel-like stroma of the chloroplast, this reaction uses ATP and NADPH to make glucose (an energy store).

6H2O(l) + 6CO2(g) C6H12O6(aq)+ 6O2(g)Light, Chlorophyll



Backtrack – Plant Structure – Big Picture



Backtrack – Plant Structure – Close Up

Stroma

• Gel surrounding grana

Thylakoid

• Specialized membranes that contain pigments

Granum

• A stack of thylakoid disks



Light- Dependent Reaction - What We Know:

• Sunlight is a form of radiant energy that can be broken down to a stream of discrete energy levels corresponding to the colors of the rainbow (ROYGBIV). Each color wavelength has it’s own energy level, with Violet having the highest energy and red having the lowest energy.

• A pigment is a molecule that absorbs light. The pigment chlorophyll (which is a combination of chlorophyll a and chlorophyll b) is the molecule that absorbs sunlight during photosynthesis.

• Chlorophyll does not absorb all wavelengths of light. Which do you think they absorb? Let’s test this out!



Absorbance spectrum is a graph that shows the relative amounts of light of different colors that a pigment absorbs.

• Which colors are not absorbed by chlorophyll?

Challenge Questions:

What is the advantage to a plant of having more than one pigment?

Why do leaves turn red-orange in the fall?



Action spectrums for photosynthesis measure oxygen production at different wavelengths of light to see where photosynthesis occurs the most (why measure oxygen production?)

At what wavelengths would you expect to see the most oxygen production?



Light- Dependent Reactions - What We Don’t Know:

• The light-dependent reaction occurs in the thylakoid membrane and can be summarized as such:

Light

12 H20

6 02

Light- Dependent Reactions

ATP, NADPH

ADP, NADP+




Steps in Light-Dependent Reactions (pg 173-174):

• Within the thylakoid membrane there are two types of pigment clusters called photosystems. The photosystems contain chlorophyll and other pigments, as well as a molecule that will accept electrons (become reduced).

• When light is absorbed by the pigments in the photosystems, they pass the energy in a form of an electron to the electron acceptor. This reduced molecule can now pass the energy along the electron transport chain and finish the light-dependent reactions in 5 steps.

• NOTE: Your textbook describes 4 steps, but I include chemiosmosis as the fifth step (pg 174).




PSII

PSI

Step 1: Pigments in PSII absorb light and electron moves to the electron acceptor.

The electron is replaced by photolysis (water is split to release hydrogen ions, oxygen, and an electron).




PSII

PSI

Step 2: The electron is passed through a series of electron acceptors in the ETC. Each transfer causes a small release of energy, which is enough to push hydrogen ions into the thylakoid space.




PSII

PSI

Step 3: Light is absorbed by pigments in PSI and an electron moves to the electron acceptor.

The electron is replaced by the electron that has moved down the previous ETC.




PSII

PSI

Step 4: The second electron moves down the electron transport chain. This final electron acceptor is NADP+, which is then reduced to form NADPH.




Step 5: The hydrogen ions that were forced into the thylakoid space pass through a protein called ATP synthase. The energy from this facilitated diffusion is used to convert ADP into ATP. This process is called chemiosmosis.



Monday’s Class Starts Here!



Recap 1 – label the parts



Recap 2: The light-dependent Reactions

• The light-dependent reaction occurs in the thylakoid membrane and can be summarized as such:

•ATP and NADPH that form in the stroma are now used in the light-independent reactions.

Light

12 H20

6 02


ATP, NADPH

ADP, NADP+

Check this out!

http://www.mcgrawhill.ca/school/applets/abbio/ch05/phothospo_cyclic_and_no.swf



Recap 3- what happens to hydrogen?

In the light-dependent reactions, water is split by light to produce an electron, oxygen, and hydrogen ions. Where do these hydrogen ions go (hint: there are two possible destinations).



•Write the exhilarating tale of Eric the excited electron!

•Use your class notes and textbook to explain the details of how a electron travels from a water molecule to NADPH (feel free to be creative!)

•When finished, switch with someone else and have them check to make sure all steps are included and in the correct order.




PSII

PSI

Step 4: The second electron moves down the electron transport chain. This final electron acceptor is NADP+, which is then reduced to form NADPH.



Electron transport chain

• An ETC is a series of redox reactions that slowly release the energy from a hydrogen’s electrons and traps the energy in the chemical bonds of ATP.

This energy is used to make ATP!



Adenosine Triphosphate (ATP)

• All cellular processes require ATP for energy (muscle contraction, moving chromosomes during cell division, moving cilia, active transport of waste products).

• ATP is an adenosine molecule with three phosphates attached:

Adenosine P P P

Adenosine P P

PEnergy released for cellular processes

P

ADP

ATP

Energy gained in cellular respiration

NOTE:

Plants just don’t “do photosynthesis”. They need ATP

too. So, after they produce glucose in photosynthesis, they

break it down in cellular respiration to form ATP!

Reduction

http://www.uic.edu/classes/bios/bios100/f06pm/taxi.jpg



Light- Independent Reactions - What We Don’t Know:

• The light-independent reactions occur in the stroma and can be summarized as such:

6 CO2 6 H2OLight- Independent Reactions

ATP, NADPH

ADP, NADP+

C6H12O6

(glucose)



Steps in Light-Independent Reactions (pg 176-177):

• The energy of ATP and NADPH can be used to synthesize glucose in the stroma of chloroplasts. Since sunlight is not directly needed in these reactions, they are called light-independent.

•The series of reactions needed to produce glucose from carbon dioxide form a cycle known as the Calvin-Benson cycle. Although there are many reactions involved, there are only three main stages you need to understand.



Carbon Dioxide Fixation

6 CO2

Replacing

RuBP

Reduction

X 12

PGAL x 12

PGAL x 2

PGAL x 10

RuBP x 6

•The carbon from CO2 bonds to a 5-carbon molecule ribulose bisphosphate (RuBP) to form an unstable compound that, through several different reactions, will eventually become glucose.

• This process requires energy (ATP) and reducing power (from NADPH). When this energy and reducing power is used, ADP and NADP+ are byproducts.

• Let’s put the order of the Calvin-Benson cycle in order using the puzzle pieces.

• Make note of the changes in number of carbons at each stage.



Summary of Photosynthesis

6 CO2

6 H2OLight- Independent Reactions

ATP, NADPH

ADP, NADP+

Light

12 H20

6 02


ATP, NADPH

ADP, NADP+

C6H12O6


Cancel the intermediates, and what do you get?

• Review P.179 #1,2,7,8,11,12



Popeye knew what he was doing! Photosynthesis & Cellular Respiration

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