Photosynthesis prt II

Question 1

Noncyclic Electron Flow Summary:

1. … energy is transformed into … energy in the form of … and …
2. where do the electrons come from originally? what happens to the molecule involved?
3. what is the basic route that electrons travel?
4. what happens between the 2 photosystems?

Answer 1

1. light energy, chemical energy. in the form of ATP and NADPH
2. from H2O molecules in the thykaloid space; releases oxygen
3. H2O –> PSII –> ETC –> PSI –> ETC –> NADP+
4. electrons move down ETC and fuel ATP production

Question 2

what is the following element responsible for/steps it takes in the noncyclic electron flow:
Accessory pigment molecules
-where is it found?

Answer 2

1. absorbs photons of light energy
2. energy is passed from pigment molecule to pigment
   molecule until it reaches Chlorophyll A (in reaction center)
3. Energy excites electrons in Chlorophyll A molecules to high-energy state
   -found in light-harvesting complex both in PSII & PSII

Question 3

what is the following element responsible for/steps it takes in the noncyclic electron flow:
Chlorophyll A
-where is it found?

Answer 3

• found in reaction center in both PSII & PSI
  1. accepts electrons from H2O molecules in thylakoid space
  2. holds electrons until energy is transferred to it from accessory pigment molecules –> which then alters electrons into high-energy state
  3. electrons in high-energy state transferred to primary electron acceptor

Question 4

what is the following element responsible for/steps it takes in the noncyclic electron flow:
water
-where is it found?

Answer 4

1. molecule splits
2. two of its electrons are donated to the Chlorophyll A pigment molecules in the reaction centre to replace the lost electrons
3. Oxygen is released
   - found in thykaloid space

Question 5

what is the following element responsible for/steps it takes in the noncyclic electron flow:
primary electron acceptor

Answer 5

1. accepts high energy electrons from chlorophyll A molecules
2. high energy electrons are then passed to ETC

Question 6

what is the following element responsible for/steps it takes in the noncyclic electron flow:
Electron transport chain (1)

Answer 6

1. collects high-energy electrons from primary electron acceptor in PSII and passes to the Chlorophyll A molecules in the reaction centre of PSI through series of oxidation-reduction reactions between proteins
2. ETC (1) is essential for the synthesis of ATP.
   energy released as the electrons move from high energy state to a lower energy state –> this is used to move move H+ across the thylakoid membrane, against their concentration gradient.
   -The energy stored in this H+ gradient will be used to synthesis ATP.

Question 7

which direction do hydrogen ions move through thykaloid membrane?

Answer 7

hydrogen ions pumped into thykaloid space ( greater hydrogen concentration), diffuse out of thykaloid space (diffusing down it’s gradient) through atp synthase

Question 8

where does chlorophyll A in PSI get its electrons?

Answer 8

from electrons passed down ETC from PSII

Question 9

what is the following element responsible for/steps it takes in the noncyclic electron flow:
electron transport chain (2)

Answer 9

1. collects high-energy electrons from PSI primary electron acceptor
2. very short ETC
3. high-energy electrons pass through NADP+ reductase which passes the electrons to NADP+ –> reducing it to NADPH

Question 10

what is the simple summary process of noncyclic electron flow photosynthesis?

Answer 10

photon –> light energy to pigment molecules –> other pigment molecules –> energy to chlolophyll A in PSII ( electrons here from H2O) –> energy boosts electrons to primary electron acceptor –> ETC (1) (energy from this result in ATP synthesis) –> electrons to chlorophyll A in PSI –> boosted to primary electron acceptor (from photon energy from pigment molecules) –> ETC (2) –> NADP+ reductase –> electrons passed to NADP+ –> NADPH

Question 11

what is the cyclic electron flow? where do electrons move to/from? what does it produce? what does it not produce?

Answer 11

Alternate path that photoexcited electrons can take
-Electrons move from Chlorophyll A to primary electron acceptor in PSI, through an electron transport chain, and back to Chlorophyll A in PSI
-Produces: ATP (energy created through ETC, fuels movement of H+)
-No release of oxygen
-no NADPH produced
SUMMARY: Electrons cycle through electron acceptors and PSI, instead of travelling all the way down ETC(2)

Question 12

how is cyclic electron flow achieved?

Answer 12

instead of continuing down ETC(2) electrons are diverted to a molecule in ETC(1)

Question 13

why is cyclic flow needed?

Answer 13

Cyclic flow is required because more ATP is needed

for the Calvin Cycle than NADPH

Question 14

where is the energy stored to synthesis ATP during photosynthesis? how is this made, where does this energy come from? what happens after this is made?

Answer 14

-energy stored in H+ gradient across the thylakoid membrane
-H+ gradient is created when ETC actively transports
H+ across the membrane –> Energy used for this active transport comes from exergonic (energy releasing reaction) ‘fall’ of electrons down ETC (1)
-H+ will diffuse down it’s concentration gradient (to area of lower H+ concentration), and does this through a transmembrane transport protein –> ATP synthase
-as H+ diffuses down its gradient, energy is released and captured by ATP synthase, and used to phosphorylate ADP + P(i) to make ATP which is an endergonic reaction (energy consuming)

Question 15

besides active transport, what are 2 other ways that H+ gradient is made across thykaloid membrane?

Answer 15

1. due to release of H+ when water splits inside of thykaloid space, creating higher H+ concentration
2. removal of H+ from stroma (outside thykaloid membrane) by reduction of NADP+ –> into NADPH, creating lower H+ concentration

Question 16

what are the forms of energy that come from light reactions? what are they used for?

Answer 16

1. ATP
2. NADPH
   - used to synthesize sugar in Calvin cycle

Question 17

what is the purpose of the calvin cycle? what are the inputs/outputs of the calvin cycle? how many turns of the cycle does it take?

Answer 17

-to synthesize sugar
inputs:
3 CO2
9 ATP
6 NADPH
outputs:
3-carbon sugar

-it takes 3-turns of the cycle to create one 3-carbon sugar

Question 18

what are the 3 phases of the calvin cycle?

Answer 18

1. carbon fixation
2. reduction
3. regeneration

Question 19

what happens during the carbon fixation phase?

Answer 19

1. CO2 combined with 5-carbon organic molecule to form 6-carbon molecule

::: CO2 + 5-carbon org molecule –> 6-carbon org molecule

2. 6-carbon molecule breaks down into two 3-carbon organic molecules

::: 6-carbon molecule –> 2X 3-carbon molecule

3. For every 3-CO2 molecules entering the Calvin
   cycle six 3-carbon organic molecules are produced

::: 3X CO2 + 3X 5-carbon org molecule –> 3X 6-carbon org molcule –> 3X (2X 3-carbon molecule)

Question 20

what happens during the reduction phase?

Answer 20

1. Energy from ATP and high-energy electrons from NADPH added to the 3-carbon organic molecules
2. The 3-carbon organic molecules are reduced to
   3-carbon sugar molecules called G3P

::: 3-carbon org molecule + ATP + NADPH (electrons) –> G3P (3-carbon sugar molecules)

3. Six 3-carbon sugars are formed for every 3-CO2
   molecules that enter = two 3-carbon sugars per turn
4. One 3-carbon sugar is released from the cycle per
   three turns of the cycle
5. 3-carbon sugar = product of photosynthesis

::: 3X CO2 + 3X 5-carbon org molecule –> 3X 6-carbon org molcule –> 3X (2X 3-carbon molecule) + ATP + NADPH –> 6X G3P (3-carbon sugars)

Question 21

what happens during the regeneration phase?

Answer 21

1. The 5 remaining 3-carbon sugars are used to
   reform the three 5-carbon organic molecules
   - Energy from ATP is used to regenerate these 5-
   carbon organic molecules

::: 5X 3-carbon sugars –> 3X 5-carbon org molecules

Question 22

what is the CO2 acceptor in the calvin cycle

Answer 22

3x 5-carbon organic molecules