Semester 1 Final: Photosynthesis

Question 1

light dependent reaction

Answer 1

Pigments (chlorophyll & carotenoids) in thylakoids capture sun energy & convert it into energy carrier molecules (ATP & NADPH) with oxygen released as a byproduct from splitting water
Where: the thylakoid
What’s made: ATP, NADPH, & oxygen
Why: to create electron carriers utilized in the light independent reaction

Question 2

steps of light-dependent reaction

Answer 2

1. Light is absorbed by Photosystem II and energy is passed between pigment
   molecules
2. H2O is split, releasing 2H+ into the thylakoid lumen, 2 e- to P680 and releasing O2 as a byproduct.
3. At the reaction center, when energy arrives, two electrons are boosted out of two chlorophyll molecules
4. First electron carrier accepts the two energized electrons that are then passed through an ETC
5. Energy released from ETC is used to pump H+ into thylakoid lumen from the stroma (the H+ ion concentration gradient used to drive ATP synthesis via chemiosmosis)
6. Light energy absorbed by Photosystem I is passed to the reaction center chlorophyll
7. Two high energy electrons boosted and ejected from reaction center (the electrons lost by PS I are replaced using electrons from PS II)
8. Electrons passed down electron transport chain for PS I
9. The two electrons, NADP+
   , and H+ ion are used to form 1 NADPH molecule

Question 3

Calvin cycle

Answer 3

NADPH & ATP from light-dependent reactions are used to power glucose synthesis therefore, light not directly necessary
 AKA: Calvin Cycle or C3 Cycle
 Where: the stroma
 What’s made: G3P (glucose)
 Why: to make glucose

Question 4

Steps of Carbon Cycle

Answer 4

carbon fixation, reduction, regeneration

Question 5

Carbon Fixation

Answer 5

CO2 is linked to a carbon skeleton (RuBP) by enzyme rubisco
 CO2 enters plants from air & goes into stroma
 CO2 attaches to ribulose
bisphosphate (RuBP), product of which is immediately split into two molecules of phosphoglycerate (PGA)

Question 6

Reduction

Answer 6

carbohydrate is formed at the expense of ATP and NADPH
 PGA is energized by ATP & reduced by NADPH from the light reactions to make glyceraldehyde-3-phosphate
(G3P)
 G3P removed from this part of the Calvin cycle represents the carbohydrate product of photosynthesis
 G3P is a three-carbon sugar-phosphate that can be used to make a range of carbohydrates by other
pathways

Question 7

Regeneration

Answer 7

the CO2 acceptor RuBP reforms at the expense of ATP
 The remaining G3P is converted into more ribulose bisphosphate (RuBP) so that the Calvin cycle can continue
 Requires an ATP and more than one G3P to give the total of five carbons found in RuBP

Question 8

C3 Plants

Answer 8

When stomata partially close on hot & dry days the amount of sugar produced greatly decreases
 This causes photorespiration (O2 entering the Calvin cycle which uses energy & decreases photosynthetic output)
 Examples: Rice, wheat, & soybeans

Question 9

C4 Plants

Answer 9

Alternate mode of carbon fixation that creates four carbon compound
 Adaptations to minimize photorespiration
 Combines phosphoenolpyruvate (PEP) with CO2 prior to Calvin Cycle by PEP carboxylase
 PEP carboxylase has lower affinity for O2
 Examples: sugarcane, corn, & grasses

Question 10

CAM Plants

Answer 10

Carbon fixation is called crassulacean acid metabolism
 Adaptation for arid conditions
 Open stomata during the night & close them during the day
 Organic acids created at night are stored in the vacuole until day when the light reaction supplies ATP & NADPH
 Examples: succulents, cacti, & pineapples