Photosynthesis in Higher Plants - NEET Previous Year Questions with Complete Solutions

Non-cyclic photophosphorylation involves both PSI and PSII, produces ATP, NADPH, and O₂, and is the standard pathway. Cyclic photophosphorylation involves only PSI, produces only ATP (no NADPH, no O₂), and electrons cycle back to the same chlorophyll molecule. NEET frequently tests which products are generated by each pathway, so memorise this distinction clearly.

The first stable product of CO₂ fixation in C3 plants is 3-Phosphoglycerate (3-PGA), a 3-carbon compound. CO₂ combines with RuBP (a 5-carbon molecule) via the enzyme RuBisCO to form an unstable 6-carbon intermediate that immediately splits into two molecules of 3-PGA. This reaction is the defining step of the Calvin cycle.

NEET typically includes 3 to 5 questions from Photosynthesis in Higher Plants every year. This is based on NTA's official question papers from 2013 to 2024. The chapter falls under the Plant Physiology unit, which as a whole accounts for roughly 12–15% of total Biology marks. Consistent practice of PYQs from this chapter directly improves your NEET Biology score

PEP Carboxylase (PEPCase) is the primary carboxylation enzyme in C4 plants. It fixes CO₂ in mesophyll cells by combining it with PEP (Phosphoenolpyruvate) to form Oxaloacetate (OAA), a 4-carbon compound. PEPCase has a much higher affinity for CO₂ than RuBisCO and does not react with O₂, which is why C4 plants have negligible photorespiration and higher photosynthetic efficiency at high temperatures.

Kranz anatomy refers to the wreath-like arrangement of bundle sheath cells around vascular bundles, found exclusively in C4 plants like maize and sugarcane. These cells contain large chloroplasts and high concentrations of RuBisCO. CO₂ is first fixed in mesophyll cells (as OAA) and then pumped into bundle sheath cells, preventing photorespiration. Any NEET question mentioning Kranz anatomy points to a C4 plant answer.

Photorespiration occurs across three organelles: chloroplasts, peroxisomes, and mitochondria. It begins when RuBisCO binds O₂ instead of CO₂, forming phosphoglycolate. This wasteful process consumes O₂ and releases CO₂ without generating ATP or sugar. It occurs predominantly in C3 plants and is essentially absent in C4 plants due to their CO₂ concentrating mechanism.