5.2.4 - Light-dependant Reactions

Question 1

What Does The LDR Rely On?

Answer 1

Light.

Question 2

What Does The LIR Rely On?

Answer 2

Products made from the LDR.

Question 3

Where Does The LDR Take Place Within The Chloroplast?

Answer 3

Thylakoid membrane.

Question 4

Where Does The LIR Take Place Within The Chloroplast?

Answer 4

Stroma.

Question 5

What Is The Photolysis Of Water?

Answer 5

Light energy enables the splitting of water molecules.

Question 6

What Happens During The Photolysis Of Water In Light-Dependent Reactions?
(3 Points + 3 Sub-Points)

Answer 6

~ Photolysis of one molecule of water produces:
-> 2 hydrogen ions (2H+), also known as protons
-> 2 electrons (2E-)
-> 1 atom of oxygen (O)

~ The hydrogen ions and electrons are used during the light-dependent reactions.

~ Oxygen is given off as a waste product.

Question 7

During The LDR, What Is Light Energy Converted Into?

Answer 7

Chemical energy in the form of ATP and reduced NADP.

Question 8

What Type Of Enzyme Is NADP?

Answer 8

Coenzyme.

Question 9

What Is The Role Of NADP In The LDR?

Answer 9

Transfer hydrogen from one molecule to another.

Question 10

What Happens When NADP Gains Hydrogen?

Answer 10

It is reduced and can be known as either reduced NADP or NADPH.

Question 11

Describe The Acronym OIL RIG
(2 Points)

Answer 11

~ Oxidation -> loss of electrons and hydrogen -> gain of oxygen.

~ Reduction -> gain of electrons and hydrogen -> loss of oxygen.

Question 12

How Can Reduced NADP Reduce Other Molecules?

Answer 12

By giving away hydrogen.

Question 13

How Can NADP Oxidise Other Molecules?

Answer 13

By receiving hydrogen.

Question 14

What Are ATP & NADPH Produced During?

Answer 14

LDR as a result of photophosphorylation on the thylakoid membrane.

Question 15

What Does Photophosphorylation Mean?
(2 Points)

Answer 15

~ Photo -> Light.

~ Phosphorylation -> The addition of phosphate (ADP to form ATP)

Question 16

What Are The Two Types Of Photophosphorylation?

Answer 16

~ Non-cyclic photophosphorylation.

~ Cyclic photophosphorylation.

Question 17

What Does Cyclic Photophosphorylation Produce?

Answer 17

Cyclic photophosphorylation produces ATP only.

Question 18

What Does Non-cyclic Photophosphorylation Produce?

Answer 18

Non-cyclic photophosphorylation produces both ATP and NADPH.

Question 19

What Do Both Cyclic & Non-cyclic Photophosphorylation Involve?
(2 Points)

Answer 19

~ A series of membrane proteins making up the electron transport chain.

~ Chemiosmosis, where energy released from electrons passing down the chain is used to produce ATP.

Question 20

What Happens In The Electron Transport Chain During Photophosphorylation?

Answer 20

Electrons pass from one protein to another along the chain, releasing energy.

Question 21

What Is Chemiosmosis?

Answer 21

The energy released as electrons pass down the electron transport chain is used to produce ATP.

Question 22

Describe The Steps Involved In Non-Cyclic Photophosphorylation?
(15 Points)

Answer 22

~ Light energy hits photosystem II in the thylakoid membrane.

~ Two electrons gain energy and become excited to a higher energy level.

~ The excited electrons leave the photosystem and pass to the first protein in the electron transport chain.

~ As excited electrons leave photosystem II, they are replaced by electrons from the photolysis of water.

~ These electrons pass down the electron transport chain.

~ Energy is released as the electrons pass down the chain, enabling chemiosmosis.

~ H+ ions are actively pumped from the stroma to the thylakoid space, generating a concentration gradient across the thylakoid membrane.

~ H+ ions diffuse back across the thylakoid membrane into the stroma via ATP synthase enzymes.

~ The movement of H+ ions causes ATP synthase to catalyse the production of ATP.

~ At the end of the electron transport chain, electrons from photosystem II are passed to photosystem I.

~ Light energy also hits photosystem I, exciting another pair of electrons.

~ The excited electrons from photosystem I pass along another electron transport chain.

~ These electrons combine with hydrogen ions and NADP+ to form reduced NADP (NADPH).

~ H+ + 2e- + NADP+ -> NADPH.

~ The reduced NADP and ATP pass to the light-independent reactions.

Question 23

Describe The Steps Involved In Cyclic Photophosphorylation?
(9 Points)

Answer 23

~ Light hits photosystem I.

~ Electrons are excited to a higher energy level and leave the photosystem.

~ Excited electrons pass along the electron transport chain, releasing energy.

~ The released energy drives the process of chemiosmosis.

~ H+ ions are actively pumped from a low concentration in the stroma to a high concentration in the thylakoid space, creating a concentration gradient across the thylakoid membrane.

~ H+ ions diffuse back into the stroma via ATP synthase enzymes in the membrane.

~ The movement of H+ ions causes ATP synthase to catalyse ATP production.

~ At the end of the electron transport chain, electrons rejoin photosystem I, completing the cycle (cyclic photophosphorylation).

~ The produced ATP enters the light-independent reaction.