Glossary

•  ATP - Adenosine triphosphate.  ATP is the major source of chemical energy in cellular processes.  When hydrolysed it loses one phosphate to become adenosine diphosphate (ADP) and releases usable energy.
•  Bundle sheath cells -  Special cells found in leaves of C4 plants in which the 4 carbon acids formed initially in the mesophyll cells are decarboxylated and CO₂  is fixed by Rubisco.  These cells are characterized by thick walls which increase CO₂  concentrations near the Rubisco sites, prevent CO₂  from leaking out of the cells and enhance carbon fixation over photorespiration.
• C3 plants - Carbon  fixed from CO₂ is assimilated during the first stage of the PCR pathway into two identical three-carbon products (3-phosphoglycerate, 3PGA). Found in all major plant families or in about 300,000 species.  Typical C3 plants include: barley, sunflower, rice, tomatoes, wheat, peanuts, cotton, sugar beet, oats, and most trees.
• C4 plants -  In C4 plants, the first stable products of carbon assimilation are 4-carbon carboxylic acids produced.  Cellular differentiation occurs which spatially regulates carbon assimilation. The 4 carbon acids are formed in the mesophyll cells and are then transferred to special cells (bundle-sheath cells) where they are decarboxylated and the CO₂ released is then fixed by Rubisco in the PCR cycle.
• Carboxylase - An enzyme incorporating CO₂  into an organic compound with a carboxyl group.
• Chlorophyll a - The major pigment of photosynthesis.  Found in all plants.
• Decarboxylate - Removal of a carboxyl group (COOH) from a molecule.  CO₂  is produced.
• Gross photosynthesis (Pg) - The total fixation of energy by photosynthesis.
• Guard cells - Cells in the leaves of higher plants surrounding the stomatal pores. Changes in the shape of the guard cells causes the stomata to open or close.
• Hatch Slack pathway - Pathway of carbon fixation in C4 plants.  Carbon is assimilated into C4   Discovered and described by Marshall Hatch and Roger Slack
• Krantz anatomy - Characteristic of C4 plants. Plant veins are encased by thick-walled photosynthetic bundle-sheath cells that are surrounded by thin-walled mesophyll cells.
• Light-compensation point - The amount of light at which photosynthesis and respiration balance (i.e. net photosynthetic rate of a plant = 0). For a plant like wheat this is about 5 Wm-2.
•  NADP/NADPH - Nicotinamide adenine dinucleotide phosphate.  A coenzyme that functions as an electron acceptor/donator in many of the redox reactions within cells.  Obtained in the light-reactions of photosynthesis and used to reduce carbon dioxide.
•  Net photosynthesis (Pn) -  The actual rate of production of new biomass .  This is essentially gross photosynthesis minus the rate of respiration.
•  PEP carboxylase (PEPCASE)  - The enzyme responsible for the carboxylation of CO₂  in the mesophyll cells of C4 plants into oxaloacetate.
•  Photorespiration - Uptake of oxygen in the light by Rubisco (which also acts as an oxygenase) and the consumption of carbohydrate.  This process competes with photosynthetic CO₂  uptake and carbohydrate synthesis.  Photorespiration increases in dry hot climates when conditions limit CO₂  availability and favor high oxygen concentrations.
•  Primary productivity - The rate of biomass production per unit area by plants.
• Redox reaction -  A reaction that involves reduction (gain of electrons or  hydrogens – gain of oxygen) and oxidation (loss of electrons or hydrogens – loss of oxygen).
•  Respiration - The breakdown of organic molecules such as sugars and starches into smaller components releases stored energy.  In plants, this process, the reverse of photosynthesis, consumes oxygen and releases CO_{2 .}
•  Rubisco - Ribulose bi-phosphate carboxylase/oxygenase . A bifunctional enzyme that can fix carbon dioxide or molecular oxygen, which leads to photosynthesis or photorespiration, respectively.  Rubisco is the most abundant enzyme on earth.
•  Stomata - Intracellular openings mostly found on the underside of leaves and act as valves to allow CO₂  in and out of the cells.
•  Transpiration - The process by which water vapor is lost from plants, evaporating from cell walls just below the surface of the leaf and diffusing into the air through small stomatal pores.