5.2.4 - Light-dependant Reactions

Question 1

Describe The LDR
(4 Points)

Answer 1

~ Takes place in the thylakoid membranes of the chloroplast.

~ Relies on light energy.

~ During it light energy is converted into chemical energy, as Reduced NADP and ATP.

~ The products of the LDR (ATP + Reduced NADP), are transferred to the LIR.

Question 2

Describe Photolysis
(3 Points)

Answer 2

~ Splitting of a molecule using light energy.

~ Hydrogen ions and electrons are used during the LDR.

~ Water is given off as a waste product.

Question 3

What Does The Photolysis Of One Water Molecule Produce?
(3 Points)

Answer 3

~ 2 hydrogen ions (2H+), i.e. Protons.

~ 2 electrons (2e-).

~ One oxygen atom (O).

Question 4

Describe NADP
(5 Points)

Answer 4

~ Coenzyme -> Aids the function of an enzyme.

~ Role is to transfer hydrogen from one molecule to another.

~ Once NADP gains hydrogen, it is reduced and becomes Reduced NADP or NADPH.

~ Reduced NADP, can reduce other molecules by giving away hydrogen.

~ NADP, can oxidise other molecules by receiving hydrogen.

Question 5

What Is Meant By ‘Phosphorylation’?
(2 Points)

Answer 5

~ Addition of phosphate to a molecule.

~ E.g. ADP -> ATP.

Question 6

What Is Meant By ‘Photophosphorylation’?

Answer 6

Addition of phosphate to a molecule, using light.

Question 7

What Are The 2 Types Of Photophosphorylation That Take Place In The LDR?

Answer 7

~ Non-cyclic photophosphorylation -> Producing ATP and NADPH.

~ Cyclic photophosphorylation -> Producing ATP only.

Question 8

Describe The Process Of Non-Cyclic Photophosphorylation In The LDR
(10 Points)

Answer 8

1) Light energy hits PSII.

2) This excites electrons in chlorophyll, moving them to a higher energy level.

3) These electrons are replaced by electrons from the photolysis of water, splitting water into protons, electrons and oxygen (H20 -> 2H+ 1/2 O2).

3) Electrons then leave PSII, to the first protein in the ETC.

4) As they move down the ETC, the excited electrons to release energy, which is used during chemiosmosis.

5) This energy is used to transport protons into the thylakoid, generating a proton gradient across the thylakoid membrane (Thylakoid have a higher concentration gradient than the stroma).

6) Protons (H+ Ions) move down their concentration gradient into the stroma, via the enzyme ATP synthase.

7) The energy from the movement of H+ ions, combines ADP + Pi to form ATP.

8) Light energy is reabsorbed by PSI, exciting electrons to a higher energy level.

9) Electrons pass along the ETC, combining with H ions from the photolysis of water and NADP to form Reduced NADP.

10) ATP and the Reduced NADP, pass to the LIR.

Question 9

Describe The Process Of Cyclic Photophosphorylation In The LDR
(8 Points)

Answer 9

1) Light energy hits PSI.

2) Electrons are excited to a higher energy level, leaveing the PS.

3) As they move down the ETC, the excited electrons to release energy, which is used during chemiosmosis.

4) This energy is used to transport protons into the thylakoid, generating a proton gradient across the thylakoid membrane (Thylakoid have a higher concentration gradient than the stroma).

5) Protons (H+ Ions) move down their concentration gradient into the stroma, via the enzyme ATP synthase.

6) The energy from the movement of H+ ions, combines ADP + Pi to form ATP.

7) At the end of the process, electrons rejoin PSI in a complete cycle.

8) ATP produced then enters the LIR.