module 5 - 17.4 factors affecting photosynthesis

Question 1

what are the limiting factors affecting the rate of photosynthesis?

Answer 1

• light intensity
• light quality (what wavelengths)
• carbon dioxide concentration
• temperature
• stomatal status - open or closed

Question 2

how is light intensity a limiting factor affecting the rate of photosynthesis?

Answer 2

as light increases, ATP and reduced NADP are produced at a higher rate

Question 3

how is light quality a limiting factor affecting the rate of photosynthesis?

Answer 3

light with a higher proportion of energy concentrated in these wavelengths will produce a higher rate of photosynthesis.

Question 4

how is carbon dioxide concentration a limiting factor affecting the rate of photosynthesis?

Answer 4

increasing the carbon dioxide concentration increases the rate of carbon fixation in the calvin cycle and increases rate of ATP

Question 5

how is temperature a limiting factor affecting the rate of photosynthesis?

Answer 5

• affects rate of enzyme controlled reactions
• as temp increases, rate of anzyme activity increases until proteins denature
• increase in temp increases rate of enzyme controlled reactions in photosynthesis

Question 6

how is stomatal status a limiting factor affecting the rate of photosynthesis?

Answer 6

• stomata close on leaves to avoid water loss through transpiration during dry weather
• closing stomata stops diffusion of carbon dioxide in plants, reducing rate of light independent reactions and stops photosynthesis

Question 7

what will happen if light intensity is reduced from high to low? (effect on calvin cycle)

Answer 7

1. rate of reaction of light dependent stage reduces
2. concentration of ATP and reduced NADP will reduce
3. conc. of GP increases as ATP and reduced NADP are needed to convert GP to TP so conc. of these molecules is reduces
4. conc. of TP reduces as ATP and reduced NADP are needed to convert GP to TP and conc. od ATP and reduced NADP reduces
5. conc. of RuBP reduces because of lower conc. of TP it’s made from

Question 8

what will happen if the concentration of CO2 is reduced from high to low? (effect on calvin cycle)

Answer 8

1. concentration of GP is reduced as there is less CO2 to be fixed
2. conc. of TP is reduced as there is less GP that its made from
3. conc. of RuBP increases due to lack of CO2 to be fixed

Question 9

what will happen if temperature reduces? (effect on calvin cycle)

Answer 9

1. reducing kinetic energy of all enzymes and substrates of Calvin Cyle
2. reducing number of successful collisions between enzymes and substrates
3. reducing overall rate of reaction of Calvin Cycle
4. reducing conc. of GP, TP & RuBP

Question 10

what will happen if temperature increases to high temperatures? (effect on calvin cycle)

Answer 10

1. enzymes in Calvin Cyle will be irreversibly denatured
2. reducing concentrations of GP, TP & RuBP

Question 11

what does “fixed” mean?

Answer 11

adding hydrogen to inorganic carbon from reduced NAD

Question 12

what is C4 photosynthesis?

Answer 12

• alternative to normal C3 photosynthesis
• called C4 as CO2 molecules are fixed to make a 4-carbon molecule, not by RUBISCO

Question 13

what is carbon dioxide fixed by in C4 photosynthesis?

Answer 13

• enzyme called PEP CARBOXYLASE and produces 4-carbon OXALOACETATE
• PEP CARBOXYLASE has no affinity for oxygen

Question 14

where is oxaloacetate transported in C4 photosynthesis?

Answer 14

• transported into bundle sheath cells around the vascular bundles
• it is then decarboxylated to produce carbon dioxide

Question 15

what does RUBISCO convert carbon dioxide and RuBP into, after the oxaloacetate is decarboxylated? (C4 photosynthesis)

Answer 15

• converts them into the 6-carbon intermediate and 2 GP molecules
• this means RUBISCO is shielded form oxygen produced by photolysis in the chloroplast and also has high conc. of CO2
• the 2 GP is transported back to normal photosynthetic cells

Question 16

what are C4 plants adapted to?

Answer 16

adapted to high light levels and low water levels

Question 17

what does CAM stand for?

Answer 17

crassulacean acid metabolism

Question 18

what is CAM photosynthesis?

Answer 18

alternative to normal C3 photosynthesis

Question 19

what do CAM plants do?

Answer 19

• close their stomata all day to reduce water loss by transpiration and only open them during the cooler night
• the CO2 they absorb at night is converted to malic acid
• malic acid builds up at night as a store of CO2

Question 20

what is malic acid?

Answer 20

a 4-carbon molecule

Question 21

what happens to the malic acid during the day?

Answer 21

• when stomata close, the malic acid is transported into chloorplasts
• malic acid is converted back to CO2

Question 22

what does RUBISCO use carbon dioxide and RuBP to make?

Answer 22

uses CO2 and RuBP to make the 6-carbon intermediate, rest of Calvin Cycle turns as normal

Question 23

how are CAM plants adapted?

Answer 23

adapted to high light levels and arid conditions when stomata only open at night e.g. cacti

Question 24

which 2 reactions occur during phosphorylation?

Answer 24

• ATP is synthesised
• NADP is reduced

Question 25

which reaction is catalysed by the enzyme RUBISCO?

Answer 25

carboxylation of ribulose bisphosphate (RuBP)

Question 26

which pair of areas within a chloroplast will show the steepest pH gradient between them?

Answer 26

stroma and the thylakoid space within thylakoid membrane