Photosynthasis

Question 1

Light dependent reaction

Answer 1

1. Chlorophyll absorbs light, exciting electrons - photoionisation
2. Electrons travel down ETC releasing energy
3. Creates a electrochemical gradient
4. H+ ions move through ATP synthesis
5. Providing energy to join ADP and Pi to form ATP - photophosphorylation
6. Photolysis of water produces 2 electrons 2 protons and half a oxygen
7. NADP reduced by electrons

Question 2

Light independent reaction

Answer 2

1. CO2 combines with RuBP - carbon fixation
2. Produces x2 GP
3. GP is reduced into x2 TP
4. Using energy from ATP and reduced NADP
5. TP converted back into RuBP so cycle may continue

Question 3

Suggest why ATP produced through photosynthesis is not the only source of ATP in plants

Answer 3

1. Plants cannot photosynthesise in the dark
2. Not all parts of the plant’s photosynthesis (roots)
3. Plants require more ATP than produced in LDR

Question 4

Effect of herbicide or inhibitors on ETC

Answer 4

1. Reduced electro chemical gradient across thylakoid membrane
2. So less ATP produced
3. So less reduced NADP produced
4. Light independent reaction slows

Question 5

Photoionisation

Answer 5

Chlorophyll absorbs light energy which excites electrons

Question 6

When producing a chromatogram explain why the origin is marked using pencil not ink

Answer 6

1. Ink and pigment from leaf may mix

Question 7

One advantage to plants having different colour pigments

Answer 7

Absorb more wavelengths of light for photosynthesis

Question 8

Describe the way which ATP and reduced NADP are produced in LDR

Answer 8

ATP
Light excites electrons
Energy released as they pass through ETC
ATP formed from ADP + Pi
NADP
H+ ions
Photolysis of water

Question 9

Explain how ATP and reduced NADP are used in light independent reaction

Answer 9

GP converted into TP as it is reduced using reduced NADP
ATP supplies energy for the reaction

Question 10

Describe how the structure of a chloroplast is adapted to its function in photosynthesis

Answer 10

1. Membrane provides large SA for light absorption
2. Membrane is permeable so allows diffusion of gas
3. Membrane provide surface for attachment of electrons

Question 11

When does LIR take place in the chloroplast

Answer 11

Stroma

Question 12

Explain why the amount of GP increases after a photosynthesising plant has been in darkness for short time

Answer 12

GP can’t convert to TP as requires product of LDR such as ATP and reduced NADP

Question 13

How many cycles are required of the Calvin cycle to make 1 molecule of glucose

Answer 13

6

Question 14

Similarities between photosynthesis and respiration

Answer 14

1. Transfer of energy
2. Use and produce ATP
3. Chain of election carries
4. Located on membranes
5. Involve a cycle of reactions
6. Oxidation and reduction involved

Question 15

Function of ATP

Answer 15

Provide energy

Question 16

Why does heat stress decrease light dependant reaction

Answer 16

Less ATP
Less reduced NADP

Question 17

Why is a decrease in activity of enzyme rubisco would limit rate of photosynthesis

Answer 17

Less carbon dioxide is fixing with RuBP
So less GP produced

Question 18

Two features of the calorimeter to enable valid measurement

Answer 18

Stirer - evenly distributed heat
Water has high specific heat capacity