Measurement of net leaf photosynthesis in physiological field research:

• The Infrared Gas Analyzer (IRGA, such as LI-COR LI-6400/LI-6800) is a portable field instrument that accurately quantifies photosynthetic rate and stomatal conductance.
• It measures differential differential absorption of infrared light by $\text{CO}_2$ ($4.26\text{ }\mu\text{m}$) across an open or closed leaf chamber, recording the depletion of $\text{CO}_2$ as carbon assimilation occurs.

Photorespiratory nitrogen cycle in peroxisomes:

• In the peroxisome, serine produced in mitochondria is converted to hydroxypyruvate.
• The transaminase serine:glyoxylate aminotransferase (or serine:2-oxoglutarate aminotransferase) transfers the amino group from serine to 2-oxoglutarate ($\alpha$-ketoglutarate), forming glutamate and hydroxypyruvate: $\text{Serine} + \alpha\text{-ketoglutarate} \rightarrow \text{Hydroxypyruvate} + \text{Glutamate}$.
• Hence, serine acts as the amino donor to oxoglutarate.

CO2 compensation points in C4 vs C3 plants:

• The $\text{CO}_2$ compensation point is the atmospheric concentration of $\text{CO}_2$ at which photosynthetic fixation equals respiratory plus photorespiratory release.
• In $C_4$ plants, PEP carboxylase has high affinity for bicarbonate and photorespiration is virtually absent, resulting in a very low ($0-10\text{ ppm}$, i.e. zero or nearly zero) $\text{CO}_2$ compensation point.
• Group (A): Ragi, pearl millet, Amaranthus are all $C_4$ plants.
• Group (C): Sugarcane, maize, foxtail millet are all $C_4$ plants.
• Cowpea, groundnut, and wheat are $C_3$ plants with high compensation points ($40-100\text{ ppm}$). Pineapple is CAM.