11.3 light-independent reaction Flashcards
light independent reaction
doesn’t require light directly
Uses products of ldr so ceases when light is absent
first step
CO2 from atmosphere diffused through stomata into leaf
dissolves in water around the walls of mesophyll cells
diffused through csm, cytoplasm and chloroplast membranes into stroma of chloroplast
second step
CO2 reacts with 5-carbon compound ribuslose bisphosphate(RuBP)
reaction catalysed by enzyme ribuisco(ribuslose bisphosphate carboxylase)
produces 2 molecules of 3-carbon glycerate 3-phosphate(GP)
third step
reduced NADP from ldr reduces glycerate 3-phosphate to triose phosphate(TP)
uses energy supplied by ATP
fourth step
NADP is re-formed
Goes back to ldr to be reduced again by accepting more protons
fifth step
some triose phosphate molecules converted to organic substances plant needs
-e.g. starch, cellulose, lipids, glucose, amino acids and nucleotides
most used to regenerate ribulose bisphosphate using ATP from ldr
site of light independent reaction
stroma
3 adaptions of chloroplast
- stroma surrounds grana so products of ldr can readily diffuse into stroma
- contains both DNA and ribosomes so can quickly manufacture some proteins involved
- fluid of stroma contains all enzymes needed to carry out reaction. It is membrane bound in chloroplast and separate to chloroplast so chemical environment with high conc of enzymes and substrates can be maintained
Limiting factors
- light intensity
- availability of water
- temperature
- carbon dioxide concentration
light intensity
-less light for ldr
-fewer electrons excited
-less ATP and reduced NADP for lir
-less photolysis
-fewer electrons released to replace those lost from photosystems
-less o2 is produced
-fewer stomata open so less co2 for lir
temperature (too cold)
-less kinetic energy for rubisco reactions in lir if too cold
-less RuBP carboxylated
-less GP and TP generated
-less complex molecules produced
-less ADP + Pi and NADP for LDS
-less kinetic energy for enzyme involved in photolysis if too cold
co2 concentration
-less co2 for lir
-less available to carboxylate RuBP
-less GP and TP generated
-fewer complex molecules produced
-less ADP + Pi and NADP for ldr
temperature too hot
–rubisco enzyme denatures
-electron carries in ldr renature
-proteins holding photosystems in place denature
No limiting factors
rate of photosynthesis doubles every 10 degrees between 0-25
water availability
-less h20 available for photolysis
-less o2 produced
-fewer electrons released to replace those lost from photosystems
-less ATP and reduced NADP for lir
-less H20 h20 available for guard cells to swell and stomata to open
-less co2 available for lir
-plant wilts so less SA exposed to sun for ldr