5.1 Photosynthesis - Light Independent Reaction

Question 1

where does the light independent reaction take place?

Answer 1

in the stroma of chloroplasts

Question 2

what two products are required from the LDR?
what are they used for?

Answer 2

ATP and NADPH
NADPH is used to reduce GP to TP
The hydrolysis of ATP is used to provide the energy for both the reduction of GP into TP but also for the reformation of RUBP

Question 3

which reactant of photosynthesis is used in the LIR?

Answer 3

carbon dioxide

Question 4

what does the LIR produce?

Answer 4

glucose

Question 5

How many times does the calvin cycle have to turn to form one molecule of glucose, and therefore how many ATP and NADPH are needed?

Answer 5

For every three turns of the calvin cycle, 3 carbon dioxide molecules are fixed to form TP.
Two TP molecules combine to form one molecule of glucose.
So therefore the calvin cycle needs to turn SIX times in order to produce one molecule of glucose.
By association, x12 NADPH and x18 ATP are also needed

Question 6

outline the 4 main steps of the LIR

Answer 6

1) Carbon Fixation
2) Reduction of GP into TP
3) Reformation of RuBP
4) Formation of glucose

Question 7

State and explain 3 ways in which chloroplasts are adapted to the LIR

Answer 7

1) stroma - contains the enzymes needed for carbon fixation
2) stroma - surrounds the thylakoid membranes so ATP and NADPH from the LDR can rapidly diffuse in for use
3)
DNA and ribosomes - to quickly and easily manufacture required proteins

Question 8

describe the process of carbon fixation in the LIR

Answer 8

• carbon dioxide diffuses into the stroma and is bonded to a 5-carbon sugar called ribulose biphosphate (RuBP.)
• the reaction is catalysed by the enzyme rubisco, and forms two molecules of glycerate phosphate, (GP,) a 3 carbon compound

Question 9

describe the process of reduction of GP in the LIR

Answer 9

• NADPH provides the hydrogen necessary and the hydrolysis of ATP provides the energy
• GP is reduced to form two molecules of tirose phosphate, (TP,) another 3 carbon sugar
• the ADP, Pi and NADP are returned to the thlakoid membrane to be recycled back into the LDR

Question 10

describe the process of reformation of RuBP

Answer 10

• most TP regenerates, every 5C out of 6 produced
• hydrolysis of another ATP molecule provides the required energy

Question 11

what can glucose be used for once it has been produced in the LIR?

Answer 11

• to release energy during respiration stored as starch
• to make other organic compounds eg. cellulose in cell walls
• other products it contributes towards include CO2, sucrose, amino acids and lipids