Photosynthesis: (Light Dependent Reaction)

Question 1

Light dependent reactions:

Answer 1

•the clustered arrangement of pigments in thylakoids.
•two photosystems:
-photosystem II (PSII).
-photosystem I (PSI).
•each PS has:
-about 12 chlorophyll molecules and a few carotenoids.
-a molecule that accepts electrons.
•all absorbed sunlight energy is passed to a specialized electron-accepting chlorophyll a molecule called the reaction centre.

Question 2

Photosystems:

Answer 2

-when energy is passed from the other pigments to the reaction centre, it is now “excited”.
-means the electrons have been raised to a higher energy level.
-this electron is passed to the electron accepting molecule and the molecule becomes reduced (= gains an electron) and has a higher energy level.

Question 3

Photo=

Answer 3

Light.

Question 4

Lysis=

Answer 4

Break down.

Question 5

Step 1: photolysis and PSII:

Answer 5

-photolysis: reaction starts by splitting water.
-this produces electrons, oxygen, hydrogen ions (H+).
-the electrons enter PSII.
-they then begin the process of becoming energized within the photosystem.

Question 6

Step 2: electron transport chain (ETC)

Answer 6

•the energized electron is passed through a series of electron-carrying molecules = electron transport chain.
•as the electron is passed to electron acceptors, it falls to a lower energy state.
•the released energy pushes H+ ions from the stroma into the inner thylakoid space.
•this creates a concentration gradient of H+ ions (more in the thylakoid space than in the stroma).
•this gradient provides the “push” to regenerate ATP from ADP + Pi.
•••
•energy released during ETC forces H+ across the thylakoid membrane and create a concentration gradient.
•energy from the concentration gradient is used to generate ATP from ADP and phosphate by means of chemiosmosis.
•as H+ moves down the concentration gradient, it drives the reaction that generates ATP.

Question 7

Step 3: PSI

Answer 7

•while the other steps are happening…
•light is also absorbed by photosystem I (PSI).
•energy is also transferred to a reaction centre in PSI and it too becomes excited.
•another high energy electron is passed to an electron-accepting molecule.
•the lost electron is replaced by the one from PSII after it has passed through the ETC.

Question 8

Step 4: reducing power

Answer 8

-the electron from PSI is used to reduce NADP+ into NADPH.
-the NADPH now has more energy, more “reducing power”.
-this reducing power will be used in the light independent reactions.

Question 9

Summary (light dependent reaction):

Answer 9

•an electron from water replaces the electron that was lost from photosystem II.
-the oxygen from the water molecule is converted to molecular oxygen (O2).
•when an electron from photosystem I is excited, it is eventually used to reduce NADP+ to NADPH.

Question 10

ATP synthase is:

Answer 10

An enzyme (protein) complex embedded in the thylakoid membrane that provides a pathway for hydrogen ions to move down their concentration gradient. This enzyme catalyses (causes) the formation of ATP from inorganic phosphate and ADP.

Question 11

Synthesis:

Answer 11

The process of putting together two or more components to produce an entity.

Question 12

What’s inorganic phosphate?

Answer 12

Pi.