In C4 plants like sugarcane, the carbon-fixation pathway initiates in the mesophyll cells, where CO 2 is first converted into bicarbonate. Later it is added to the three-carbon-containing molecule, phosphoenolpyruvate (PEP) during a reaction catalyzed by phosphoenolpyruvate carboxylase. The product of this reaction is the oxaloacetic acid (OAA) which is a four-carbon-containing acid. Furthermore, the OAA molecule reduces to malate, another four-carbon acid.

In the mesophyll cells, the four-carbon-containing molecule, oxaloacetic acid or oxaloacetate (OAA) is produced as a product of the reaction during which phosphoenolpyruvate (PEP) combines with carbon dioxide (carboxylation) catalyzed by an enzyme PEP carboxylase. It occurs during the Calvin cycle in photosynthesis.

Nicotinamide adenine dinucleotide (NAD) is a coenzyme present in all living cells. It is a significant molecule in cellular metabolism that plays a crucial role in energy metabolism by accepting and donating electrons. NAD comprises two nucleotides (dinucleotides) that make a bond between their phosphate groups.

A photon is the smallest discrete amount or quantum of electromagnetic radiation or small bundles of energy coming from the sunlight. It is an elementary particle without any substructure. Light energy enters the process of photosynthesis when pigments absorb it. In plants, pigment molecules absorb only visible light for photosynthesis.