UNIT 2 - LESSON 9 LIGHT DEPENEDENT RACTIONS

Question 1

STEP 1 NON CYCLICAL

Answer 1

a photon strikes a pigment in the antenna complex of photsystem ii
- the light energy is transferred from pigment molecule to pigment molecule unit it reacthes the reactio center p680 (chlorophyll a)

Question 2

step 2

Answer 2

the p680 molecule absorbs the energy which excites an electron enough to leave the molecule
- the excited electron jups from p680 to the primary electron acceptor (redox reaction: p680 has been oxidized and the primary acceptor molecule has been reduced)

Question 3

step 3

Answer 3

p680 has a hole, it is missing an electron therefore the p680+ is now positively charged, needs to fill its hole
an enzyme extracts electrons from h20/water and supplies them to the other oxidized reaction center.
this reactions splits water into two hydrogen ions, two electrons and an oxygen atom which combines with another to form o2.
this is called photolysis: the splitting of water molecule due to light energy.
the oxygen is then releasted by the plants into the environment

Question 4

where do they occur
what are reactants
what are products

Answer 4

occur in thylacoids of chloroplasts
the reactants are light and water
the products are oxygen and nadph, and atp

Question 5

step 4 (similar to etc)

Answer 5

from the primary electron acceptor, the energized electrons originating from p680 are transferred along a series of electron carrying molecules. together, these molecules are referred to as the etc
the first electron carrier will begin to move form the PEA to b6f complex once it has two electrons

Question 6

step 5 (similar to etc)

Answer 6

with each trasnfer of electrons along the system, a small amount of energy is released.
the released energy is used to pum h+ from the stroma, across the thlyakoid membrane and into the thlakoid lumen.
this pumping of electrons generate a h+ graident across the thlyakoid membrane.

Question 7

step 6

Answer 7

while step 1-5 take place, light energy is absorbed by photosystem i. this energy is transferred to the reaction cenre p700, where an electron becomes excited nad once again, is passedo nto a primary electron acceptor.
in photosystem i, the lost electron is replaced by an eelectron that has reached the end of the etc from photosystem ii

Question 8

step 7

Answer 8

two electrons that were recieved by the electron acceptor from photosystem i are used to reduce nadp+ to nadph.
the reducing power of nadph will be used in the light independent reactions

Question 9

making atp by chemiosmosis

Answer 9

atp synthesis in the light dependent reactions occurs by the same mechanism as atp synthesis in aerobic repsiration.
- since the energy source is light photons, the process is called photophosphorylation.
the use of photons of light to drive the phosphorylation of adp to produce atp via chemiosmosis

Question 10

where is chemiosmosis

Answer 10

the thylakoid membrane is impermable to hydrogen ions so they must passs thru atp synthase

Question 11

cylic electron flow

Answer 11

• the passage of one electron pair thru noncyclic electron flow generates 1nadph and slightly more than 1 atp
  this ratio of atp and nadph is not sufficent for the light independent, thus more atp is required.
• cyclic flow produces he extra atp required

Question 12

cyclic electron flow steps

Answer 12

• only photosystem i is involved in cyclic electron flow.
  an electron in p700 is excited by a photon and begins taking the same path it took in the noncyclic, however, the elctron is not used to reduce nadp+ but instead is passed back to generate the h+ gradient and generae atp.
  the same electrons that left p700 returns to fill the hole it left.

Question 13

non cyclic vs cyclic

Answer 13

the relative activities of these two photophosphorylation pathways vary depending on the relaive amounts of atp and nadph that are required by the numerous reactions that are carried out into the stroma.