Similarity between C₃ and C₄ pathway is

The similarity between C₃ and C₄ pathways is that in both cases, organic acids are formed as the first products of CO₂ fixation, although the specific organic acids differ.

In C₃ photosynthesis, the first product of CO₂ fixation is a 3-carbon compound called 3-phosphoglycerate (3-PGA). This reaction occurs in the Calvin cycle, which takes place in the stroma of the chloroplasts.

On the other hand, in C₄ photosynthesis, the first product of CO2 fixation is a 4-carbon compound, usually oxaloacetate or malate. This initial fixation of CO₂ occurs in the mesophyll cells, where the enzyme phosphoenolpyruvate carboxylase (PEP carboxylase) captures CO₂ and converts it into the 4-carbon compound.