B17

Question 1

Plants are…

Answer 1

Autotrophs (make organic compounds using CO2).

Question 2

Photosynthesis

Answer 2

6CO2 + 6H2O –> C6H12O6 + 6O2 using light energy.

Question 3

Leaf Structure (top to bottom)

Answer 3

Waxy cuticle
Upper epidermis
Palisade layer (chloroplasts)
Spongey mesophyll (xylem/phloem)
Air spaces
Lower epidermis (guard cells/stomata).

Question 4

Chlorophyll Stucture

Answer 4

Outer membrane
Inner membrane
Thylakoid (single disk)
Granum (stack)
Stroma (space inside chloroplast)
Intergranal lamella (join stacks together)

Question 5

Chlorophyll

Answer 5

Pigments (‘light absorbing molecules’) absorb different wavelengths (wl.) from sun, which maximises absorption:
Chlorophyll a (blue-green).
Chlorophyll b (yellow-green).
Cartenoids (orange carotene/yellow xanthophyll).
Blue and red yield most O2.

Question 6

Primary Pigments

Answer 6

Reaction centres made of chlorophyll a. e- excited when sun stimulates. (PRC - primary reaction centre).

Question 7

Accessory Pigments

Answer 7

Light-harvesting systems surrounding PRC. Transfer energy, boosting e- excitement.
Chlorophyll b and cartenoids.

Question 8

2 forms of Chlorophyll a which act as PRC.

Answer 8

1. Photosystem I (PSI), chlorophyll P700, wl. 700nm.
2. Photosystem II (PSII), chlorophyll P680, wl. 680nm.

Question 9

Light Dependent Reaction

Answer 9

Photolysis (splits H20, pass H to NADP to form NADPH).
Non-cyclic Photophosphorylation.
Cyclic Photophosphorylation.

Question 10

Non-Cyclic Photophosphorylation

Answer 10

Involves PSI & PSII.
Input H2O.
NADP final election acceptor, H+ reduces NADP (NADPreductase) forming NADPH.
Output NADPH & ATP & O2 (needed for LIR).

Question 11

Cyclic Photophosphorylation

Answer 11

Involve PSI only.
Produce ATP (no NADPH/O2).
No final electron acceptor as e- recycled back to PSI.
When ATP supply low and NADPH high, the amount of ATP needed for Calvin Cycle exceeds amount produced in non-cyclic. This inc. ATP supply.

Question 12

Light Independent Reaction
Calvin Cycle, Stage 1.

Answer 12

CARBON FIXATION:
1. CO2 + RUBISCO. CO2 now fixed. RUBSICO catalyses to cause GP formation from unstable 6C mol.

Question 13

Light Independent Reaction
Calvin Cycle, Stage 2.

Answer 13

REDUCTION:
2. GP phosphorylated using ATP, give energy for reduction of GP –> TP, using reducing agent NADPH (NADPH oxidised -> NADP).

Question 14

Light Independent Reaction
Calvin Cycle, Stage 3.

Answer 14

REGENERATION:
3. Most TP regenerate RuBP, uses some ATP from LDR.

Question 15

LIR Products

Answer 15

2/12 mol TP coverted to 6C glucose.
10/12 mol TP regenerated to RuBP.
1 glucose = 6CO2 enter Calvin Cycle, so 6 full turns.

Question 16

RUBISCO

Answer 16

2 active sites.
Not very specific.
Catalyse many reactions (O2/CO2 fit).
50% leaf proteins, most abundant enzyme on earth.
Inefficient (fixes 3CO2/enzymes/sec).

Question 17

Limiting Factors

Answer 17

1. Light. Inc. intensity, inc. rate until temp./CO2 limiting.
2. Temp. Inc. temp, inc rate until temp. limiting (enzymes denature, rate fall to 0).
3. CO2 conc. Inc conc, inc rate until other limiting.

Question 18

Limiting Factors effect on the Calvin Cycle

Answer 18

1. Light. Dec intensity then LDR in short supply. So GP –> TP + RuBP slow. (GP level inc & TP/RuBP dec - still used to make GP).
2. Temp. All catalysed by RUBISCO. Dec temp, dec rate. GP/TP/RuBP all dec.
3. CO2 conc. Dec conc means RuBP –> GP slow. So RuBP level inc, GP/TP dec (used to make RuBP but not remade).