Photosynthesis

Question 1

Overall Reaction of Photosynthesis

Answer 1

6 CO2 + 6 H2O + light—–> C6H12O6 + 6O2

Question 2

Stroma

Answer 2

Fluid in chloroplast

Where Calvin cycle occurs

Question 3

Lumen

Answer 3

Space inside thylakoid

H+ are pumped from stroma into lumen as electrons travel down chain

Question 4

Grana

Answer 4

Stack of thylakoids

Question 5

Pigments

Answer 5

Pigment in plant cell absorbs certain wavelengths of light to take in energy

Different pigments within cell so that different wavelengths can be absorbed

Electrons in pigment abosrb energy (are excited), re-emit to another electron

Chlorophyll a and b (green)
Carotenoids (orange, red, or yellow)

Question 6

Light Dependent Reaction

Answer 6

When energy in pigments reaches Chlorophyll A (P700) or (P680), stop bounding around

Chlorophyll P700 forms pigment cluster photosystem I

Chlorphyll 680 forms PSII

Question 7

Non-Cyclic Photophosphorylation- PSII

Answer 7

2 PSII (P60) electrons are passed to primary electron acceptor in ETC

Electrons go down chain, releasing energy as they go to lower levels (includes proteins like ferredoxin and cytochromes)

Energy used to pump protons into thylakoid lumen

ATP synthase generates ATP back into stroma

Electrons reach PSI

Once electrons reach PSI, the are energized again by light and passed to another primary electron acceptor (NADP+ not the same as in PSI)

Forms NADPH

Water split to replace electrons from PSII

O2 is released by plant

H+ provides energy needed for NADPH formation

Question 8

Cyclic Photophosphorylation

Answer 8

Instead of electrons in PSI being added to form NADPH, electrons go back to PSII to create additional ATP

Question 9

Light Independent Reaction (Calvin Cycle)

Answer 9

Fixes CO2 (CO2 originally unreactive, organic) becomes organic

To make glucose, must repeat 6 times, using 6 CO2 molecules

No light is used directly, but still needs light bc needs energy from ATP and nADPH from light reaction

Question 10

Process of Calvin Cycle

Answer 10

Carboxylation
6 CO2 + 6 RuBP —> 12 PGA (3C) Catalyzed by rubisco

Reduction
12 ATP + 12 NADPH used to convert 12 PGA—> 12 PGAL (also known as G3P)
ADP and Pi go back to non-cyclic photophosphorylation

Regeneration- 10 out of 12 PGAL molecules converted into 6 RuBP (allows cycle to continue

CHO Synthesis
2 Remaining PGAL used to form glucose

Question 11

Thylakoid

Answer 11

Membrane is where light dependent reactions take place

Where PSI and PSII are

Question 12

Chemiosmosis

Answer 12

Mechanism of ATP generation

H+ builds up in thylakoids

Lower PH in thylakoid and electrical gradient builds up

ATP synthase generates ATP

ATP generates PGAL (G3P)

Question 13

Photorespiration

Answer 13

Fixing of oxygen by rubisco protein (instead of CO2)

Rubisco not super efficient

Fixing O2 decreases amount of CO2 fixed

RuBP combines with O2 and forms PGA (phosphoglycerate) and phosphoglycolate (useless molecules, needs to be digested by peroxisomes)

Reduces photosynthesis efficiency by 25%

Question 14

C4 Photosynthesis

Answer 14

Avoids photorespiration by operating in an environment without oxygen

C4 plants can close stomato more often, preventing escape of H2O

Found in hot dry climates (can preserve their water)
- If stomata were left open, water would flow out in exchange for incoming CO2

Question 15

Stomata

Answer 15

Pores on surface of leaf where air enters/leaves

Question 16

Mesophyll cells

Answer 16

Where photosynthesis takes place

Close together, but still have some space so air can enter

Question 17

Bundle sheath cells

Answer 17

Deeper in leaf, not exposed to air

No oxygen here, only CO2

Question 18

Process of C4 Photosynthesis

Answer 18

CO2 enters mesophyll cells

Reacts with PEP instead of Rubisco, forms OAA (C4)
Catalyzed by PEP carboxylase

OAA made into malate, enters bundle sheath cells

In bundle sheath cells, malate converted into CO2 and pyruvate

Pyruavte levs and goes back to mesophyll to make more PEP

CO2 builds up in bundle sheath cell

Question 19

PEP Carboxylase

Answer 19

Can fix CO2, but not O2

Question 20

Plasmodesmata

Answer 20

Tubes connected bundle sheath cells and mesophyll cells

Question 21

CAM Photosynthesis

Answer 21

Desert plants

Stomata open up at night to prevent water loss and let CO2 in

Fixes CO2 in the same way that C4 plants do

Malate stored in storage areas at night (vacuoles)

During the day, stomata closes, malate pumped into stroma of chloroplasts

Photosynthesis continues

Question 22

Endergonic Reaction

Answer 22

Uses energy

Photosynthesis is endergonic

Question 23

Exergonic Reaction

Answer 23

Releases energy