Light Dependent Reaction

Question 1

These two stages of
photosynthesis are
known as the _____ (the photo
part of photosynthesis) and the _____ (the synthesis part).

Answer 1

light reactions & Calvin cycle

Question 2

In the _____, energy from sunlight is absorbed by chlorophyll and that energy is converted into stored chemical energy.

Answer 2

light-dependent reactions

Question 3

In the _____, the chemical energy harvested
during the light-dependent reactions drives the assembly of sugar molecules from carbon dioxide.

Answer 3

light-independent reactions (Calvin Cycle)

Question 4

Light-Dependent Reactions occur in the _____ membranes of chloroplasts.

Answer 4

thylakoid

Question 5

Light-Dependent Reactions
- The overall purpose of the light-dependent reactions is to
convert _____ into _____, that will be used by the Calvin cycle to fuel the assembly of sugar molecules.

Answer 5

light energy into chemical energy

Question 6

The light-dependent reactions consist of two electron pathways called the _____ and the _____.

Answer 6

noncyclic electron pathway and cyclic electron pathway

Question 7

Both electron pathways produce ATP, but only _____ also produces NADPH.

Answer 7

noncyclic pathway

Question 8

ATP production during photosynthesis is called _____ because light powers the process.

Answer 8

photophosphorylation

Question 9

The production of ATP during the cyclic electron pathway is called _____, whereas ATP production during the noncyclic pathway is called _____.

Answer 9

cyclic photophosphorylation, noncyclic phosphorylation

Question 10

• The actual step that converts light energy into chemical energy takes
  place in a multiprotein complex called a _____.
• two types which are found embedded in the THYROID MEMBRANE,
  _____ & _____

Answer 10

• photosystem
• photosystem II (PSII) & photosystem I (PSI).

Question 11

A photosystem consists of
_____ (molecules of chlorophyll a and chlorophyll b and the carotenoids) and electron acceptor molecules within the thylakoid membrane. The pigment complex serves as an “_____” for gathering solar energy.

Answer 11

pigment complex, antenna

Question 12

_____ drives the synthesis of ATP and NADPH by energizing the two photosystems embedded in the thylakoid membranes of chloroplasts. The key to this energy transformation is a flow of electrons through the
photosystems and other
molecular components built into the thylakoid membrane.

Answer 12

Light

Question 13

1. A photon of light strikes one of the pigment molecules in a light-harvesting complex of PS II, boosting one of its electrons to a higher energy level. This process is called _____. As this electron falls back to its ground state, an electron in a nearby pigment molecule is simultaneously raised to an excited state. The process continues, with the energy being relayed to other pigment molecules until it reaches the P680 pair of chlorophyll a molecules in the PS II reaction-center complex. It excites an electron in this pair of chlorophylls to a higher energy state.

Answer 13

photoactivation

Question 14

2. This electron is transferred from the
   excited P680 to the _____.

Answer 14

primary electron acceptor

Question 15

To replace the electron in the chlorophyll, a molecule of water is split. This splitting or also known as _____ releases an electron and results in the formation of oxygen (O2) and hydrogen ions (H+) in the thylakoid space.

Answer 15

• photolysis (water H2O splitting)

Question 16

Each photoexcited electron
passes from the primary electron
acceptor of PS II to PS I via an
ELECTRON TRANSPORT CHAIN.

The
electron transport chain between
PS II and PS I is made up of the
electron carrier ____
(PQ), _____ (b6f) complex, and a protein called _____ (PC).

Answer 16

• plastoquinone (electron carrier)
• cytochrome (b6f complex)
• plastocyanin (prote

Question 17

5. As electrons move through the proteins that reside between PSII and PSI, they _____. That energy is used to move hydrogen atoms from the stromal side of the membrane to the thylakoid lumen.

Those hydrogen atoms, plus the
ones produced by splitting water,
accumulate in the thylakoid lumen
creating a concentration gradient
will be used to synthesize ATP.

Answer 17

• lose energy (electrons energy will be used to move hydrogen atoms to the thylakoid)

Question 18

6. The electron arrives at photosystem I and joins the P700 special pair of chlorophylls in the reaction center. When light energy is absorbed by pigments and passed inward to the reaction center, the electron in P700 is boosted to a very high energy level and transferred to an _____.

Answer 18

acceptor molecule

Question 19

7. Photoexcited electrons are passed in a series of redox reactions from theprimary electron acceptor of PS I down a second electron transport chain through the protein _____.

Answer 19

ferredoxin (FD)

Question 20

8. The enzyme _____ catalyzes the transfer of electrons from Fd to NADP+ Two electrons are required for its reduction to NADPH.

Answer 20

NADP+ reductase

Question 21

Thus, PSII captures the energy to create proton gradients to _____, and PSI captures the energy to reduce _____,

The two photosystems work in concert, in part, to guarantee that the
production of NADPH will roughly equal the production of ATP. Other
mechanisms exist to fine tune that
ratio to exactly match the chloroplast’s constantly changing
energy needs.

Answer 21

make ATP, NADP+ into NADPH.

Question 22

In certain cases, photoexcited electrons can take an alternative path
called _____ electron flow, which uses photosystem I but not photosystem II.

Answer 22

cyclic

Question 23

You can see that cyclic flow is a
short circuit: The electrons cycle back
from _____ to the _____ and from there
continue on to a P700 chlorophyll in the _____ reaction-center complex.

Answer 23

ferredoxin (Fd), cytochrome complex, PS I

Question 24

In cyclic, there is no production of _____, and no release of _____, that results from this process. On the other hand, cyclic flow does generate _____.

Answer 24

NADPH, oxygen, ATP

Question 25

The chloroplast shifts to _____ when the ATP supply drops and the level of NADPH rises.

Answer 25

CYCLIC PHOSPHORYLATION

Question 26

Output:
_____ ATP
_____ NADPH

Answer 26

18 ATP
12 NADPH