RuBisCO's choice
"RuBisCO's choice" is a free, interactive Class 11 Biology simulation for NEET, built on the NCERT section "Photorespiration" in Photosynthesis in Higher Plants. RuBisCO binds whichever gas wins at the active site: CO2 gives 2 PGA, O2 gives PGA + phosphoglycolate, costs ATP and releases CO2; a C4 CO2 pump makes oxygenation vanish. NEET has asked about this idea 4 times in 10 years of papers.
From the lesson Photorespiration in Photosynthesis in Higher Plants. Change the values and watch what happens.
What it shows
NCERT §11.9
RuBisCO binds whichever gas wins at the active site: CO2 gives 2 PGA, O2 gives PGA + phosphoglycolate, costs ATP and releases CO2; a C4 CO2 pump makes oxygenation vanish.
Controls
4 to try
- SliderCO2 : O2 ratio at the enzyme 0.01–1
- Sliderleaf temperature 15–40 °C
- ToggleC3 / C4 leaf
- Readoutcarboxylations vs oxygenations, net sugar
Try this
Keep oxygenations under 5 % at 35 °C, and show it is only possible in the C4 leaf.
Common mistake
Photorespiration makes ATP or sugar.
In NEET
10 years of papers
Asked 4 times in 10 years of NEET.
See the past questions: Photosynthesis in Higher Plants (chapter)
The idea behind it
NCERT §11.9
- RuBisCO can bind both CO₂ and O₂ at its active site, and the binding is competitive: whichever gas is relatively more concentrated tends to bind. RuBisCO has a much greater affinity for CO₂ when CO₂ and O₂ are present in similar amounts.
- In C₃ plants some O₂ does bind RuBisCO. RuBP then combines with O₂ to give one molecule of phosphoglycerate and one of phosphoglycolate; this oxygenase route is photorespiration.
- Photorespiration makes no sugar and no ATP or NADPH. Instead it uses ATP and releases CO₂, making it a wasteful process.
- In C₄ plants photorespiration does not occur, because the mechanism concentrates CO₂ at the enzyme site in bundle sheath cells, so RuBisCO acts as a carboxylase and its oxygenase role is minimised.
- Lacking photorespiration helps explain why C₄ plants give better productivity and yields. They also tolerate higher temperatures. The biological function of photorespiration is still not known.
Questions
4 answers
- What does the "RuBisCO's choice" simulation show?
- RuBisCO binds whichever gas wins at the active site: CO2 gives 2 PGA, O2 gives PGA + phosphoglycolate, costs ATP and releases CO2; a C4 CO2 pump makes oxygenation vanish.
- What mistake does the "RuBisCO's choice" simulation fix?
- A common mistake it clears up: photorespiration makes ATP or sugar.
- Has NEET asked about this idea?
- Yes. NEET has asked about this idea 4 times in 10 years of papers.
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Photorespiration" in Photosynthesis in Higher Plants (Class 11 Biology).
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