6: photosynthesis

Question 1

PS II

Answer 1

1) Sunlight strikes the leaf, boosting electrons from chlorophyll (P680).
2) Electrons travel down the ETC, powering proton pumps and ATP synthase.
3) ADP + Pi are converted to ATP.
An enzyme splits H2O into protons (go into thylakoid space), oxygen (diffuses out), and electrons (replace chlorophyll’s boosted electrons).

Question 2

PS I

Answer 2

1) Electrons from PSII reach PSI, replacing the electrons previously boosted by chlorophyll.
2) Sunlight strikes the leaf, boosting electrons from chlorophyll (P700), which were originally electrons from the chlorophyll in PS II (P680).
3) After the electrons are boosted, 2 electrons and 1 H+ are taken up by NADP+, converting it to NADPH.

Question 3

Calvin Cycle

Answer 3

1) Rubisco combines 3 RuBP (from previous cycle) with 3 Co2 molecules, becoming 6 PGA molecules.
2) ATP is converted to ADP + Pi, and the phosphate (Pi) attaches to the 6 PGA, turning them into 6 DPGA.
3) NADPH donates electrons and protons to 6 DPGA, turning them into 6 PGAL. NADPH goes back to NADP+.
4) 1 PGAL exits the cycle.
5) The remaining 5 PGAL are rearranged by 3 ATP breaking down into ADP + Pi, releasing free energy to rearrange the molecules.
6) 3 RuBP are regenerated.

Question 4

Light-dependent reactions location

Answer 4

Thylakoid membrane

Question 5

Calvin Cycle location

Answer 5

Stroma (of thylakoid)

Question 6

C4 plants

Answer 6

1) In mesophyll cells, PEP carboxylase binds PEP and Co2 (carbon fixation), forming a 4C compound, oxaloacetate.
2) Oxaloacetate is converted to a 3C molecule and is transported to the bundle sheath cell.
3) The 3C molecule breaks down into Co2 in the bundle sheath cell, which goes through the Calvin Cycle as normal. PEP is regenerated.
-> Only Co2 (not O2) is being pumped into bundle sheath cells (where rubisco is found), minimizing photorespiration.

Question 7

CAM plants

Answer 7

1) At night: stomata open, allowing O2 to leave and Co2 to enter.
2) Co2 diffuse in, binding with PEP (same system as C4 plants), and Co2 molecules are stored in vacuoles until daytime.
3) Daytime: stomata close and plants use the Co2 they stored during the nighttime in the Calvin Cycle to produce glucose.
-> Since the stomata close during the Calvin Cycle (daytime), Co2 is more plentiful than O2 (to a certain degree). Then, when O2 builds up, it isn’t a problem because rubisco in CAM plants has a lower affinity for O2 than C3 plants.

Question 8

Difference between C4 and CAM

Answer 8

C4: carbon fixation happens in mesophyll cells, and the rest of the Calvin Cycle happens in bundle sheath.
CAM: also uses C4 pathway, but everything happens in one (mesophyll) cell.

Question 9

Pigments polarity (least polar to most polar)

Answer 9

Beta-carotene
Xanthophyll
Chlorophyll a
Chlorophyll b

Question 10

C4 plant growth

Answer 10

Rapid growth in hot climates

Question 11

CAM plant growth

Answer 11

Slow growth (despite being adapted to avoid photorespiration) due to limited Co2 intake at night