Photosynthesis & Cellular Respiration

Question 1

Where does photosynthesis occur?

Answer 1

Chloroplast

Question 2

What are the stages involved in photosynthesis and where do they occur?

Answer 2

Light dependent stage (thylakoid membrane)
& light independent stage (stroma)

Question 3

What happens in light dependent stage?

Answer 3

1) Light energy is absorbed by photosynthetic pigments in photosystems to excite high energy electrons from chlorophyll pigment
2) high energy electrons are passed through a chain of electron carriers and proton pumps in electron transport chain (ETC)
3) energy released in the process is used by proton pumps to transport protons from STROMA into THYLAKOID space via active transport
4) protons move back from THYLAKOID space to STROMA through HYDROPHILIC channel provided by ATP synthase via facilitated diffusion.
5) ATP is formed from ADP+Pi, as ATP synthase harnesses proton-motive force to generate ATP (chemiosmosis)
6) final electron acceptor NADP+ combine with electrons and proton (from stroma) to form NADPH, reaction catalyses by NADP reductase
7) photosystem receives replacement of electrons from photolysis of water, which produces electrons, hydrogen and oxygen

Question 4

What are the products of light dependent reaction?

Answer 4

ATP, NADPH oxygen

Question 5

What are the reactants of the light dependent reaction?

Answer 5

Electrons, ADP+Pi, NADP, light energy, water, photosynthetic pigments

Question 6

What happens in light independent stage? (Hint: crR)

Answer 6

1) carbon fixation
A process in which 1 molecule of CO2 combines with 5C RuBP to form an 6C intermediate, catalyses by enzyme RUBISCO
6C intermediate is unstable, hence will break down to give 2 molecules of 3C compound
2) reduction
ATP breaks down into ADP (energy) and Pi, NADPH reduces 3C compound to GALP
3) RUBP regeneration
Some GALP exits Calvin Cycle, and is used as starting material for metabolic pathways that synthesise organic compounds (glucose)
Some GALP remains to regenerate RuBP
ATP will be used again to provide energy for rearrangement of C atoms between sugar phosphates, basically form back RuBP
ADP and Pi will be recycled at thylakoid membrane for light-dependent reactions

Question 7

What are the initial reactants needed for Light independent cycle?

Answer 7

CO2
RuBP

Question 8

What is the rate of Light Independent stage dependent on?

Answer 8

Temperature (catalyses by several enzymes)
CO2 concentration

Question 9

Alternative name for Light Independent stage?

Answer 9

Calvin Cycle

Question 10

Products of Light Independent Stage?

Answer 10

ADP, Pi, NADP, GALP

Question 11

RuBP full name?

Answer 11

Ribulose Biphosphate

Question 12

GALP full name?

Answer 12

Glyceraldehyde-3-phosphate

Question 13

What are the aerobic respiration processes & where do they occur?

Answer 13

1) glycolysis, cytosol
2) Kreb’s cycle, mitochondrial matrix
3) link reaction, mitochondrial matrix
4) oxidative phosphorylation p, inner membrane of mitochondria

Question 14

What is the process of glycolysis?

Answer 14

1) phosphorylation of hexose
- 2 ATP is used in the phosphorylation of hexose to make it more reactive

2) splitting of 6C sugar
- 6C sugar intermediate will split to form 2 GALP/ triose phosphate (3C)

3) oxidation/dehydrogenation of triode phosphate
- each 3C sugar is oxidised by 1 molecule of NAD
These NADH will carry high energy electrons extracted from bonds of glucose, to be channeled into oxidative phosphorylation to make ATP
4) substrate level phosphorylation of 3C sugar
- each 3C sugar undergoes a series of step to form pyruvate.

Overall, glucose forms 2 pyruvate. Require 2 NAD to oxidise glucose. Form 2 net ATP per glucose

Question 15

What is the process of Link reaction?

Answer 15

Pyruvate travels to mitochondrial matrix to undergo oxidative decarboxylation.
A carbon is removed from pyruvate to form CO2, and coenzyme A (coA) will join the 2 carbon molecule to form acetyl coA.
NAD is used to oxidise pyruvate to acetyl coA, itself being reduced to NADH, to be channeled to oxidative phosphorylation.

Overall, 1 glucose=2 pyruvate=2 co2 formed to diffuse out of cell= 2 NAD needed to oxidise and thus form 2 NADH= 2 acetyl coA formed

Question 16

What is the process of Krebs Cycle?

Answer 16

1) acetyl coA is taken up by oxaloacecate to form 6C compound
2) 6C compound undergoes oxidative decarboxylation to produce 5C compound + co2. NAD oxidises the reaction, forming NADH.
3) 5C compound undergoes further O.D to produce 4c compound + co2 + nadh
4) 4c compound undergoes substrate level phosphorylation, which is to form ATP. FAD and NAD oxidises reaction to form FADH & NADH.
5) oxaloaceate is formed AGAIN, cycle repeats

Question 17

What is the process of oxidative phosphorylation?

Answer 17

1) NADH & FADH2 carry high energy electrons extracted from glucose to inner mitochondrial membrane
2) electrons are transferred to electron transport chain, finally to oxygen, the final electron acceptor. Oxygen combines with hydrogen and electrons to form water
3) energy released from passage of electrons is used by proton pump to actively transport protons from mitochondrial matrix to intermembrane space, creating proton gradient
4) protons diffuse back into matrix via hydrophilic channel provided by ATP synthase, via facilitated diffusion
5) ATP synthase harness proton motive force to generate ATP from ADP +Pi.
1 NADH = 3 ATP, 1 FADH2 = 2ATP
1 GLUCOSE= 34 ATP