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Flashcards in Photosynthesis Deck (34):
1

6CO2 + 6 H20 + light ----->

C6H12O6 + 6O2

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"excited" electrons

These energized electrons are unstable and almost immediately re-emit the absorbed energy.

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Two main processes of photosynthesis: Light-dependent and light-independent reactions

Define them

1. Light-dependent- The light reactions use light energy directly to produce ATP that powers the light-independent reactions.

2. Light-independent reactions - This reaction consists of the Calvin cycle, which produces sugar. To power the production of sugar, the Calvin cycle uses ATP formed during the light reactions.

Both reactions occur when light is present.

4

Photosynthetic pigments

absorbs light energy and use it to provide energy to carry out photosynthesis.

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Non-cyclic Photophosphorylation-
Light dependent reaction:

1.Photosystem II

Electrons trapped by P680 in photosystem II are energized by light.

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Non-cyclic Photophosphorylation-
Light dependent reaction:

2. Primary electron acceptor

Two excited e- passed to a primary electron acceptor; called primary because it is the first in chain of acceptor.

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Non-cyclic Photophosphorylation-
Light dependent reaction:

3.Electron transport chain

Consists of a plastoquinone complex (PSII) which contains proteins like CYTOCHROME and cofactor Fe+; analogous(comparable) to oxidative phosphorylation.

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Non-cyclic Photophosphorylation-
Light dependent reaction:

4.Phosphorylation

2e- (electrons) move "down" the chain---> they lose energy.(energy used to phosphorylate about 1.5 ATP.)

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Non-cyclic Photophosphorylation-
Light dependent reaction:

5.Photosystem I

e- transport chain terminates with PS I(with P700).

They are again energized by sunlight and passed on to another primary e- acceptor. From this point forward, it can go to cyclic or noncyclic. If noncyclic then....

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Non-cyclic Photophosphorylation-
Light dependent reaction:

6. NADPH

2e- then pass down a short electron transport chain( with proteins like FERRODOXIN) to combine NADP+ plus H+ 2e- --------> NADPH(coenzyme)
Like NADH in respiration, NADPH is an energy-rich molecule.

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Non-cyclic Photophosphorylation-
Light dependent reaction:

7. Splitting of Water

The loss of 2e- from PSII(initially) is replaced when H20 splits into 2e-, 2H+, and 1/2 O2 (H+ goes for NADPH formation and 1/2 O2 that contributes to release as oxygen gas. This occurs at PSII.

{H20 + ADP + Pi + NADP+ plus light ---> ATP + NADPH + O2 + H+}

12

Light-dependent reactions or simply light reactions.

H20 + ADP + P + NADP+ + light ---->

In summary, photophosphorylation takes the energy in light and the electrons in H20 to make the energy-rich molecules ATP and NADPH. Because the reactions require light, the are called LIGHT-DEPENDENT reactions.

ATP + NADPH + O2 + H+.

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Cyclic Photophosphorylation

This replenishes ATP when Calvin cycle consumes it.

-When excited 2e- from PSI join with protein carriers in the first electron transport chain and generate 1 ATP as they pass through; these 2e- are recycled into PSI and can take either cyclic or noncyclic path.

14

Calvin Cycle:

Step 1. Carboxylation

Step 1. fixes CO2, repeat 6 times, uses 6CO2 to produce C6H12O6(glucose)

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Calvin Cycle:

Step 2. Reduction

Step 2.) 12 ATP and 12 NADPH-----> 12G3P or 12PGAL; energy is incorporated; by-products(NADP+ and ADP) go into non-cyclic phosphorylation.

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Clavin Cycle:

Step 3. Regeneration

3.) 6 ATP convert 10 G3P----> 6RuBP. (allows cycle to repeat)

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Calvin Cycle:

Step 4: Carbohydrate Synthesis

State what is does and it's formula.

The remaining 2 G3P are used to build glucose and other monosaccharides like fructose and maltose.

6O2 + 18ATP + 12NADPH + H+ ------> 18ADP + 18Pi + 12NADP+ plus 1 glucose(2G3P)

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Light-independent reactions/dark reactions

No light directly used in the Calvin cycle.

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Chloroplasts:

1. Outer membrane

This membrane, like plasma membrane, consists of a double layer of phospholipids.

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Chloroplasts:

2. Intermembrane space

Area in between inner and outer membranes,

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Chloroplasts:

3. Inner membrane

This is the second membrane. This is also a double phospholipid bilayer.

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Chloroplasts:

4. Stroma

Where the light-independent reactions occur.

Fluid material that fills inside the inner membrane.mThe Calvin Cycle occurs here, fixing carbon from CO2 to generate carbohydrate precursors(G3P).

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Chloroplasts:

5. Thylakoids

Within the stroma are stacks of pancake-like membranes.

Individual membrane layers are THYLAKOIDS.

An entire stack of thylakoids is a granum.

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Chloroplasts:

6. Thylakoid lumen

This is the inside(lumen) of the thylakoid. H+ ions(protons) accumulate here.

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Chemiosmosis

the mechanism of ATP generation that occurs when energy is stored in the form of a proton concentration gradient across a membrane.

Th

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Chemiosmosis in Chloroplasts:

Step 1:

1. H+ ions(protons) accumulate inside thylakoids.

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Chemiosmosis in Chloroplasts:

Step 2:

A pH and electrical gradient across the thylakoid membrane is created.

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Chemiosmosis in Chloroplasts:

Step 3. ATP synthases generate ATP

Channel proteins called ATP synthases, allow the H+ to flow through the thylakoid membrane and out to the stroma.

The energy generated by the passage of the H+ provides the energy for the ATP synthases to phosphorylate ADP to ATP.

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Chemiosmosis in Chloroplasts:

Step 4

The Calvin cycle produces 2G3P using NADPH and CO2 and ATP at then end of the e- transport chain following PSI, 2e- produces NADPH.

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Photorespiration:

Fixation of oxygen by rubisco---> produces no ATP or sugar. Not 'efficient' because rubisco will fix both CO2 and oxygen at the same time if both are present.

Peroxisomes breakdown the products of this process.

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Peroxisomes:

They are found near chloroplasts, where they function to break down photorespiration products.

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Caretenoids

red,orange, yellow.

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Antenna pigments

Chlorophyll b, carotenoids, phycobilins(red algae pigment) capture wavelengths that chlorophyll a does not.

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C4 Photosynthesis

Evolved from C3, when CO2 enters leaf; absorbed by mesophyll cells; instead of being fixed by rubisco into PGA, CO2 combines with PEP to form OAA by