Photosynthesis

Question 1

What are photoautotrophs?

Answer 1

Generate own organic matter through photosynthesis

Question 2

Why are plants green? What are the two types of pigment and the three types of chloroplast pigment?

Answer 2

Pigments absorb some wavelengths of light and reflect others
chlorophyll reflects green 
CAROTENES, XANTHOPHYLLS
-Chlorophyll a
- Chlorophyll b
- carotenoids

Question 3

What is chromatography?

Answer 3

Separation of pigments

Question 4

What is the equation for chromatography?

Answer 4

Rf= distance moved by pigment/ distance moved by solvent (short distance/ long distance)

Question 5

What does an absorption spectrum show?

Answer 5

Graph showing how much light of different wavelengths is absorbed by a pigment (strong in blue and red regions, carotenoids= blue- green regions)

Question 6

What does an action spectrum show?

Answer 6

Graph showing rate of photosynthesis are different wavelengths- closely correlated with absorption spectra- suggests these pigments are involved in photosynthesis

Question 7

What are the two types of reactions in photosynthesis?

Answer 7

1) light dependant reaction
solar energy –> electrical energy –> chemical energy
end products = ATP, NADPH2
2) light independent reaction
reduce CO2 to make glucose
ATP provides energy, NADPH2 provides hydrogen

Question 8

What is a photosystem? What are the two categories?

Answer 8

Arrangement of photosynthetic pigments within the thylakoid membrane
1) primary pigments
two forms of chlorophyll a with slightly different absorption peaks- form reaction centres
2) Antenna/ accessory pigments
other forms of chlorophyll a & b & carotenoids- form antenna complex which acts as funnel

Question 9

How do photosystems work?

Answer 9

• Light absorbed by photosystem
• antenna pigments pass light energy to primary pigment in reaction centre
• primary pigment contains pair of electrons
• light energy excites electrons and emitted from reaction centre
• electrons used in light dependant reactions

Question 10

What are the two types of photosystem?

Answer 10

1) photosystem I
arranged around molecule of chlorophyll a
absorbs wavelength at 700nm
2) photosystem II
arranged around molecule of chlorophyll a
absorbs wavelength at 680nm

Question 11

Where does the light dependant reaction take place? What are the two types reaction?

Answer 11

Thylakoid membrane (photolysis in thylakoid space, ATP in stroma)

Question 12

What happens in non-cyclic phosphorylation?

Answer 12

• light absorbed by antenna pigments in PS1 and transferred to reaction centre
• energy excites and emits electrons
• electrons to ETC, ‘left’ at end
• for PS1 to keep emitting e- need to be replaced by e- from PSII
• Photolysis occurs in thylakoid membrane space (H20—> H+, e-, O2)
• H+ to membrane space and down electrochemical gradient through ATP synthase generating ATP (chemiosmosis)
• electrons provide energy to pump H+ from stroma–> TS
• electrons ‘left’ combine with NADP
  NADP + 2e- + 2H+ –> NADPH2
• ATP and NADPH2 passed to calvin cycle

Question 13

What is cyclic phosphorylation?

Answer 13

• PSII emits e- and passed to ETC but passed back to PSII

- No NADPH2 produced but can take place without water but still needs light to emit and excite electrons

Question 14

Where does the light independent reaction take place? What is the process called?

Answer 14

Stroma

Calvin cycle

Question 15

Describe the calvin cycle

Answer 15

CO2 added to ribulose bisphosphate (5C) enzyme ribulose bisphosphate carboxylase
unstable 6C compound produced
splits in two
2X glycerate phosphate 
2X NADPH2--> NADP, 2X ATP --> ADP-Pi
2X triose phosphate ( to glucose for starch, lipids, cellulose sugars etc) 
Ribulose phosphate 5C
ATP--> ADP (Pi added to substrate)
Ribulose bisphosphate

Question 16

How many turns of the calvin cycle are needed to produce one molecule of glucose?

Answer 16

for every 6 triose phosphate molecules, 5 are regenerated to ribulose phosphate and 1 is converted to glucose
6 TURNS OF CYCLE NEEDED FOR 1 GLUCOSE MOLECULE

Question 17

What is the carbon fixation stage in the calvin cycle?

Answer 17

CO2 combines with ribulose bisphosphate catalysed by ribulose bisphosphate carboxylase

Question 18

What is the reduction stage in the calvin cycle?

Answer 18

Glycerate phosphate reduced to triose phosphate using NADPH2 and ATP

Question 19

What is the regeneration stage in the calvin cycle?

Answer 19

Triose phosphate regenerated to ribulose phosphate- ATP provides energy and phosphate