A2 - photosynthesis

Question 1

Process of light dependent reaction

Answer 1

-chlorophyll molecule absorbs light energy and a pair of e- is raised up energy level (excited) . e- leave chlorophyll - chlorophyll is ionised (photoionisation)
-excited e- passed from e- carrier to e- carrier in a series of redox reactions. series of e- carriers is located in the thylakoid membrane. each e- carrier is a lower energy level than previous one so e- loose energy
-the energy is used to pump H+ into the thylakoid space
-H+ move from high conc inside thylakoid to a lower conc in the stroma, through atp synthase.
Atp synthase comines ADP+Pi to form ATP
-H+ pass through ATP synthase and are taken up (along with e- bu NADP to form NADPH)
-Photolysis - splitting water with light provide e- to replace those lost from chlorophyll during photoionisation

Question 2

importance of the LDR

Answer 2

-transfer of energy fro light to chemical (in form of ATP ) is important as ATP is needed as a source of energy and phosphates in LIR
-in LIR ATP hydrolysis provides energy and phosphates needed to convert GP > TP molecules
-if this did not happen then no organic molecules such as glucose could be formed and so this would reduce respiration from occuring thus reducing ATP synthesis which means metabolic processes cannot occur

Question 3

role of photolysis in LDR

Answer 3

-splitting water with light
-so provides e- to replace those lost from chlorophyll molecule during photoionisation
-h+ pass through atp synthase and are taken up (along with e-) by NADP to from NADPH

Question 4

What are the H+ ions produced in photolysis used for?

Answer 4

-picked up by NADP to make NADPH

-pumped to create electrochemical gradient and diffuse through ATP synthase (allowing ATP to be formed)

Question 5

importance of LDR

Answer 5

The light-dependent reactions use energy from sunlight to produce oxygen and convert ADP and NADP+ into the energy carriers ATP and NADPH. These reactions also produce oxygen as a by-product.

Question 6

LIR process

Answer 6

1) Co2 enters stroma via diffusion and reacts with RuBP (5C)
- catalysed by rubisco
2) FoRMS 2x GP (3C)
3) NADPH from LDR used to reduce GPinto TP using energy from ATP
$)NADP is reformed and goes back to LDR to be reduced again by accepting more H+
5) some TP converted to useful organic substances eg glucose, strach, cellulose, nucleotides ect
6) most TP used to regenerate RuBP using ATP from LDR

Question 7

Explain how ATP and reduced NADP are used in the light-independent reaction of photosynthesis.

Answer 7

GP converted to triose phosphate / GALP;
this involves reduction;
reduced NADP provides reducing power / hydrogens; ATP supplies energy for this reaction; phosphate from ATP; for production of RuBP;