Light-dependent Reactions

Question 1

What happens in the LD reactions?

Answer 1

Light is absorbed and solar energy is converted into chemical energy

Question 2

What are the products of LD reactions in terms of light-independent reactions?

Answer 2

The reactants for LI.

Question 3

What are the reactants of LD reactions?

Answer 3

NADP+ (H+ and e- acceptor), H2O (is split to release H+, e-, and O2), and light (energized e- to continue process).

Question 4

What are the products of LD reactions?

Answer 4

NADPH+H+ and ATP. (O2 exits)

Question 5

What are the major steps of LD reactions?

Answer 5

Absorption of light and photolysis of H2O.

Question 6

What is light energy used for?

Answer 6

To produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen.

Question 7

What is photophosphorylation?

Answer 7

The process of generating ATP from ADP and phosphate by means of a proton-motive force generated across the thylakoid membrane of the chloroplast.

Question 8

What is chemiosmosis?

Answer 8

An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP.

Question 9

When is an electron excited?

Answer 9

When the electron is at a higher energy level due to the chlorophyll absorbing light.

Question 10

When is a chlorophyll photoactivated?

Answer 10

When the electron is excited.

Question 11

How do single chlorophyll molecules re-emit energy?

Answer 11

The excited electron drops back down to its original level, which re-emits energy.

Question 12

Where is chlorophyll located within the cell?

Answer 12

In the thylakoid membrane, within photosystems.

Question 13

What is the first step in linear electron flow?

Answer 13

The photon energy excites pigment moleculesi n PSII, bouncing energy until it reaches e- in P680 (chlorophyll a)

Question 14

What are P680 and P700?

Answer 14

These are reaction center chlorophyll. They best accept 680nm and 700nm.

Question 15

Where are P680 and P700 found?

Answer 15

P680: PSII. P700: PSI

Question 16

What is the second step in linear electron flow?

Answer 16

Electrons from P680 move to primary e- acceptor.

Question 17

What is the third step in linear electron flow?

Answer 17

H2O is split filling P680 with e-, which releases O2 and H+ proteins.

Question 18

What is step number four in linear electron flow and why is it so important?

Answer 18

e- moves from PSII through e- transport chain. This powers cytochrome C, moving H+ from stroma to thylakoid space (photophosphorylation in terms of chemiosmosis).

Question 19

Describe step five in linear electron flow. This step is also very important because…

Answer 19

ATP synthase is activated by the gradient (chemiosmosis) to make ATP (photophosphorylation).

Question 20

What is step six in linear electron flow?

Answer 20

e- moves to PSI to re-energize via ferredoxin. This repeats.

Question 21

What is step seven in linear electron flow?

Answer 21

e- reduces NADP+ to NADPH+H+ (for the Calvin Cycle)

Question 22

Which way do hydrogen ions flow in photosynthesis to form the gradient?

Answer 22

From the thylakoid space to the stroma.

Question 23

In cellular respiration, which way do hydrogen ions flow to form the gradient?

Answer 23

From the intermembrane space to the matrix.

Question 24

Is energy released at more place than one?

Answer 24

Yes, but only at th ATP synthase is there enough energy released to form a molecule or ATP.

Question 25

What is the coupling of electron transport to ATP synthesis?

Answer 25

Chemiosmosis!

Question 26

In the light-dependent reactions/linear electron flow, where do the three components come from when NADP+ is reduced to NADPH+ +H+?

Answer 26

2 electrons come from the electron transport chain an done hydrogen ion comes from the stroma.

Question 27

How does PSII replace the excited electrons it gives away?

Answer 27

Through PHOTOLYSIS, which splits water molecules in the thylakoid space.

Question 28

Is the special chlorophyll moleule at the reaction center negatively or positively charged after giving away an electron?

Answer 28

Positively charged.

Question 29

What is photolysis and where does it happen?

Answer 29

The splitting of water molecules, which occurs in light. This happens within the thylakoid space.

Question 30

What are the products of photolysis?

Answer 30

1/2 of an Oxygen molecule and 2 hydrogen ions.

Question 31

What is special about cyclic electron flow in terms of photosystems?

Answer 31

It uses PSI, NOT PSII. The electron cycles back from ferredoxin to the cytochrome complex.

Question 32

What is different about cyclic electron flow in terms of oxygen, water, and NADPH+H.

Answer 32

No oxygen is produced, no water is needed, and no NADPH+H is made.

Question 33

Why is the normal flow of electrons in the thylakoid membrane inhibited when cyclic flow occurs?

Answer 33

Because NADP+ is needed as the final accpetor of electrons.

Question 34

What can cyclic electron flow do?

Answer 34

It acts as an alternative route that allows for ATP production when NADP+ is not available.

Question 35

What is cyclic photophosphorylation?

Answer 35

The cyclic electron flow.

Question 36

In cyclic electron flow, where do the excited electrons come from when they arrive at the cytochrome complex?

Answer 36

From the primary electron acceptro in photosystem I.