light independent reaction (calvin cycle)

describe the stages of the light independent reaction (Calvin cycle):

• CO₂ reacts w/ RuBP to form unstable 6C compound - catalysed by rubisco

• 6C compound splits into 2x GP molecules

• ATP and NADPH from LDR are used to reduce GP to triose phosphate

• some triose phosphate used to regenerate RuBP in the Calvin cycle, using ATP

• some triose phosphate converted to useful organic substances

which enzyme catalyses ADP + Pi → ATP?

ATP synthase

which enzyme catalyses ATP → ADP + Pi?

ATP hydrolase

discus the efficiency of the Calvin cycle:

low:

• one hexose sugar (e.g. glucose) is made by joining 2 molecules of TP

• 5/6 Cs used to regenerate RuBP

• so Calvin cycle needs to happen 6x to make 1 hexose sugar

how does lack of light cause the amount of radioactively labelled GP to increase? what caused the amount of radioactively labelled glucose to decrease after the light was switched off?

• ATP and NADPH not formed so GP is not being used to form RuBP

• glucose used in respiration / formation of starch/cellulose

between 0 and 300 secs, the conc of radioactive GP is constant - why?

RuBP combines w/ CO₂ to produce 2x GP

between 300 and 380 secs, the conc of radioactive RuBP increases - why?

• less used to combine w/ CO₂ 

• less used to form GP

why may the % of C in a leaf not reach 0?

any 2 from:

• some used to make cellulose/cell walls

• some converted into starch

• not all fixed/used in photosynthesis OR not enough RuBP

• some used to reform RuBP/some still in GP

explain why a lower rate of sucrose transport would cause a decrease in dry mass of a plant:

• increased conc of sucrose in leaves inhibits rubisco ∴ less CO₂ fixed into GP/combines w/ RuBP/Calvin cycle/LIR

• less sucrose transported to roots, so roots do not develop/grow

• roots less develop so fewer minerals available for growth

• less growth → less dry mass