The light-dependent reactions in plants

Question 1

Where do light-dependent reactions occur?

Answer 1

-In the membranes

Question 2

In Photosynthetic bacteria what is their photosynthetic membrane?

Answer 2

-The plasma membrane itself

Question 3

Why is the thylakoid membrane important?

Answer 3

-Bc it contains structures that are involved in light-dependent reactions which is they are called Thylakoid reactions

Question 4

What are the 4 stages of thylakoid reactions?

Answer 4

• Primary photoevent
• Charge separation
• Electron transport
• Chemiosmosis

Question 5

What is the Primary Photoevent stage of Thylakoid reactions?

Answer 5

-This is where a photon of light is captured by a pigment & excites an electron within the pigment

Question 6

What is the Charge Separation stage of Thylakoid reactions?

Answer 6

-The excitation energy from the electron is transferred to the reaction center by transferring an energetic electron to an acceptor molecule= initiates electron transport

Question 7

What is the Electron Transport stage of Thylakoid reactions?

Answer 7

• This is where the excited electrons are shuttled along a series of electron carrier molecules embedded within the photosynthetic membrane
• Some of these molecules react by transporting membrane protons across the membrane= generates a proton gradient
• The electrons are then reduced to NADPH

Question 8

What is the Chemiosmosis stage of Thylakoid reactions?

Answer 8

-The protons that accumulate on one side of the membrane now flow back across the membrane through ATP synthase= where chemiosmotic synthesis of ATP takes place

Question 9

What are the 2 stages of the Light-dependant reactions?

Answer 9

• The first stage is the capturing energy from light which makes up stage 1-3 for the thylakoid reactions
• The 2nd stage is the generation of ATP which is the 4th stage of the thylakoid reactions

Question 10

What is Cyclic Photophosphorylation?

Answer 10

• That a single photosystem in purple & green bacteria is used to generate ATP via electron transport & that process returns the electrons back to the reaction center
• These systems are Anoxygenic

Question 11

What is the peak absorption for purple nonsulfur bacteria?

Answer 11

• It occurs at a wavelength of 870nm= not visible to the human eye
• which is why they use the pigment P870 in the reaction center

Question 12

What happens when P870 reaction center absorbs a photon?

Answer 12

-The excited electron is passed to an electron transport chain that passed the electrons back to the reaction center= generates a proton gradient for ATP synthesis

Question 13

What is the peak absoprtion for the green sulfur bacteria?

Answer 13

-It occurs at a wavelength of 840nm

Question 14

What happens to the green sulfur photosystem?

Answer 14

• Excited electrons can either be passed to NADPH or returned to chlorophyll by an electron transporter chain (like the one in purple bacteria)
• Then use electrons from hydrogen sulfide to replaced those passed to NADPH

Question 15

What do the proteins for the purple bacterial photosystem appear to be homologous with?

Answer 15

-The proteins are homologous to the proteins in the modern photosystem II

Question 16

What do the proteins for the green bacterial photosystem appear to be homologous with?

Answer 16

-The proteins are homologus to the proteins in the modern photosystem I

Question 17

What do the photosystem of purple & green bacteria have in common?

Answer 17

• They both don’t generate sufficient oxidizing power to oxidize H2O
• They are both anoxygenic & anaerobic

Question 18

Why is having 2 linked photosystems better than having the cyclic photophosorylation?

Answer 18

• The linked systems aren’t as limiting like the cyclic one
• It provides an alternative source of electrons from the oxidation of water which also generates O2= oxygenic photosynthesis
• The transfer of electrons also produces NADPH= can be used in biosynthesis of carbs

Question 19

What are the 2 photosystems for plants?

Answer 19

• Photosystem I

- Photosystem II

Question 20

What is the absoption peak of Photosystem I?

Answer 20

• The peak is 700nm

- So its reaction center pigment is P700

Question 21

What is Photosystem I?

Answer 21

• It can pass electrons to NADP+ which produces NADPH

- The electrons lost are replaced by electrons from Photosystem II

Question 22

What is the absoprtion peak of Photosystem II?

Answer 22

• The peak is 680nm

- So its reaction center pigment is P680

Question 23

What is Photosystem II?

Answer 23

-It can generate an oxidation potential high enough to oxidize water to replace the electrons transferred to Photosystem I

Question 24

What happens when Photosystem I & II work together?

Answer 24

-They carry out a transfer of electrons that generate both ATP & NADPH

Question 25

How is Photosystem I & II connected?

Answer 25

-They are connected by the electron carriers= Cytochrome/b6-f complex

Question 26

What is the Cytochrome/b6-f complex?

Answer 26

• It connects photosystem I & II together
• This complex can use energy from the passage of electrons to move protons across the thylakoid membrane to generate the proton gradient used by ATP synthase enzyme

Question 27

LEFT OFF

Answer 27

P 157