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32 Cards in this Set

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Tissue on the interior of a leaf containing most chloroplasts. Typical cell has 30 – 40 chloroplasts
Microscopic pores where CO2 enters and O2 exits
Envelope of of 2 membranes encloses the stroma. Elaborate sustem of interconnected thylakoid membrane segregates the stroma from another compartment


Formula for photosynthesis

6 CO2 + 12 H2O + light =C6H12O6 + 6O2 + 6H2O
Where does the O2 in carbs produced by plants come from?
Comes from H2O not the CO2
2 parts of photosynthesis
Light reactions and dark reactions.
Light reactions

Light absorbed by chlorophyll drives a transfer of electrons and hydrogen from H2O to NADP+ to NADPH. Also generates ATP of a phosphate group to ADP.

Production of ATP powered by by light during light reactions in photosynthesis.
Carbon fixation
First step of the Calvin Cycle where CO2 is incorporated from air into organic molecules already in the chloroplast.
Where are the sites of the 2 photosynthesis steps

Thylakoids to the light reactions and the Calvin cycle occurs in the stroma.

What colors of light does chlorophyll absorb?
Red and blue
Chlorophyll a (α)
Absorbs red and blue light. Only pigment to directly convert light energy. Other pigments transfer absorbed light energy to Chlorophyll a.
Chlorophyll b
Yellow green light absorbing pigment.
Hydrocarbon accessory pigments of yellow and orange that also help photoprotect chlorophyll
Reaction center

Where first light driven process of photosynthesis occurs. A chlorophyll a and a primary electron acceptor are next to each other. Chlorophyll a loses an electron to the acceptor.

Chlorophyll with proteins and other smaller organic molecules. A photosystem has a light gathering antenna complex consisting of a cluster of a few hundred chlorophyll a, chlorophyll b, and carotenoid molecules.
Photosystem 1
Has P700 chlorophyll at reaction center
Photosystem 2
Has P680 chlorophyll
Noncyclic electron flow (concept)
Produces NADPH and releases oxygen. This uses both photosystem 1 and 2. Produce ATP and NADPH in equal quantities.
Cyclic electron flow description and why is it used

Uses photosystem 1, but not 2. The electrons cycle back from ferredoxin to the cytochrome complex and from there continue on to P700 chlorophyll. Produces ATP but no NADPH or O2. The Calvin Cycle uses more ATP than NADPH, so if ATP runs low the cell uses cyclic electron flow to regenerate ATP stores.

Noncyclic electron flow (steps)
1) in photosystem 2 P680 loses electrons and becomes a strong electron acceptor.2) an enzyme extracts elevtrons from H2O donates to P680, splitting H2O to 2 H+ and the O combines with another to make O2. 2) an enzyme extracts electrons from H2O donates to P680, splitting H2O to 2 H+ and the O combines with another to make O2. 3) Photoexcited electrons from photosystem 2 pass through and electron transport chain similart to in respiration. 4) as electrons are passed energy is harnessed by thylakoid membrane to make ATP (non-cyclic phosphorylation). 5) When it hits the bottome of the tchain the electron fills a hole in P700. 6) Primary electron acceptor of photosystem 1 passes excited electron to a second transport chain which transfers them to ferredoxin. NADPH reductase gives it to NADP+ to make NADPH
Product of Calvin cycle
Glyceraldehyde 3 phosphate (G3P). To make this the cycle has to turn 3 times.
Calvin Cycle phase 1
Carbon fixation. Incorporates each CO2 by attaching it to a 5 carbon sugar called ribulose biphospate (RuBP) by RuBP carboxylase or rubisco. Product is a 6 carbon intermediate that splits to 2 molecules of 3 phosphoglycerate.
Calvin Cycle phase 2

Reduction. Each 3 phosphoglycerate gets a phosphate from ATP becoming 1,3 phosphoglycerate. NADPH reduces it to G3P. For 3 CO2 we get 6 G3P. 1 goes to plant to use but the other go to phase 3.

Calvin Cycle phase 3

Regeneration of CO2 acceptor. 5 Molecules of G3P make 3 molecules of RuBP spending 3 more ATP.

Net usage to make 1 G3P
Calvin Cycle uses 9 ATP and 6 NADPH
On hot days stomata close and decrease CO2 intake and increase trapped O2. Uses VO2 in the Calvin Cycle breaks down sugar and makes CO2. Counterproductive. Happens because Rubisco is somewhat attracted to O2 and at high levels it is a competitive inhibitor of carbon fixation.
C4 photosynthesis
Carbon fixation forms a 4 carbon compound as its first product. 2 distinct anatomical differences in plants that can do C4 photosynthesis. They contain mesothyll cells and bundle sheaths.
Bundle sheath cells
Arranged in tightly packed sheaths around veins. Light reactions of the Calvin cycle happens only here in C4 photosynthetic plants. PEP is shipped to these cells keeping CO2 concentrations high in these cells.
Has a higher affinity for CO2 than rubisco and with the help of PEP carboxylase binds to it to be sent to bundle sheath cells in C4 plants.
CAM plants (crusselacean acid metabolism)

In succulents. Plants open stomata at night and close during the day. Mesophyll cells store organic acids made at night in vacuoles until morning to be incorporated into sugar by chloroplasts.