Q.Describe the C4 pathway in outline, referring to Kranz anatomy and explaining why it allows C4 plants to photosynthesise efficiently under hot, high-light conditions.

In the C4/Hatch-and-Slack pathway, CO2 is first fixed onto PEP (a 3-carbon compound) in mesophyll cells.

The Hatch and Slack (C4) pathway is found in plants adapted to hot, dry, and bright conditions (e.g. maize, sugarcane). Here, atmospheric CO2 is first fixed in the mesophyll cells by combining with the 3-carbon acceptor phosphoenolpyruvate (PEP), catalysed by the enzyme PEP carboxylase (PEPcase), forming the 4-carbon compound oxaloacetic acid (OAA) — hence the name 'C4 pathway'. OAA is converted to malate/aspartate and transported to the bundle sheath cells, where CO2 is released and re-fixed via the Calvin cycle (using RuBisCO and the acceptor RuBP), while a 3-carbon compound (pyruvate) is recycled back to the mesophyll to regenerate PEP.

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The PEP acceptor of CO2 is found in C4 plants.

In C4 plants (e.g. maize, sugarcane), CO2 is first fixed in the mesophyll cells by the enzyme PEP carboxylase, which uses phosphoenolpyruvate (PEP, a 3-carbon molecule) as the CO2 acceptor to form the 4-carbon oxaloacetate. In C3 plants the acce …

CO2 fixation in the mesophyll cells of C4 plants is carried out by PEP carboxylase, forming the 4-carbon compound oxaloacetic acid (OAA).

C4 plants (e.g., maize, sugarcane) show Kranz anatomy, with two distinct photosynthetic cell types: mesophyll cells and bundle sheath cells. In the mesophyll cells, atmospheric CO2 combines with the 3-carbon acceptor phosphoenolpyruvate (PEP) in a reaction catalysed by the enzyme PEP carboxylase (PEPcase). Because PEP carboxylase has a much higher affinity for CO2 than RuBisCO and does not react with O2, it efficiently fixes CO2 even at low concentrations, producing the 4-carbon compound oxaloacetic acid (OAA), which is subsequently converted to malate/aspartate and transported to the bundle sheath cells. There, the 4-carbon acid is decarboxylated to release CO2, which is then fixed again by RuBisCO in the Calvin cycle (this second, …

PEP (phosphoenolpyruvate) is the primary CO₂ acceptor of the Hatch and Slack (C4) pathway, present in mesophyll cell chloroplasts.

In C3 plants, CO₂ is directly fixed by the enzyme RuBisCO onto ribulose-1,5-bisphosphate (RuBP) in the Calvin cycle, forming two molecules of 3-phosphoglyceric acid (3-PGA), a 3-carbon compound — hence the name C3 pathway. In C4 plants, CO₂ is first fixed in the mesophyll cells by the enzyme PEP carboxylase (PEPcase) onto phosphoenolpyruvate (PEP), a 3-carbon molecule, forming oxaloacetic acid (OAA), a 4-carbon compound — hence the nam …

Phosphoenol pyruvate (PEP) is the primary CO2 acceptor of the C4 (Hatch–Slack) pathway found in C4 plants such as maize and sugarcane.

C4 plants have a distinctive leaf anatomy (Kranz anatomy) with two photosynthetic cell types — mesophyll cells and bundle sheath cells. CO2 fixation happens in two stages, spatially separated between these two cell types:

1. In the mesophyll cells, atmospheric CO2 (as bicarbonate) combines with the 3-carbon acceptor phosphoenol pyruvate (PEP), catalysed by the enzyme PEP carboxylase, forming the 4-carbon compound oxaloacetic acid (OAA) — hence the name 'C4 pathway'. OAA is then converted to malic acid or aspartic acid.
2. This 4-carbon acid is transported into the bundle sheath cells, where it is decarboxylated to release CO2. This CO2 is then fixed a second time by RuBisCO via the ordinary Calvin cycle (C3 pathway, whose acceptor is RuBP), which operates in the bundle sheath. …

The first stable product in C4 photosynthesis is the 4-carbon compound oxaloacetic acid (OAA).

In C4 plants (e.g., maize, sugarcane), CO2 fixation happens in two steps across two cell types. In the mesophyll cells, the enzyme PEP carboxylase (PEPcase) -- which has a much higher affinity for CO2 than RuBisCO and no oxygenase activity -- combines atmospheric CO2 with the 3-carbon acceptor phosphoenolpyruvate (PEP) to directly produce a 4-carbon compound, oxaloacetic acid (OAA). This OAA is the FIRST STABLE PRODUCT of CO2 fixation in the C4 pathway (hence the name 'C4' …

PEP (phosphoenolpyruvate) is the molecule that first accepts CO2 in the C4 pathway.

In C4 photosynthesis, CO2 fixation begins in the mesophyll cells, where the enzyme PEP carboxylase catalyses the addition of atmospheric CO2 to the 3-carbon compound phosphoenolpyruvate (PEP), producing the 4-carbon compound oxaloacetic acid (OAA). PEP is therefore the primary (first) CO2 acceptor in C4 plants -- distinct from C3 plants, where R …

Sugar synthesis (the Calvin cycle) in C4 plants happens in the bundle sheath cells, not the mesophyll.

C4 photosynthesis is split across two cell types arranged in a characteristic 'Kranz anatomy': mesophyll cells fix atmospheric CO2 into a 4-carbon acid (via PEP carboxylase), which is then transported to the surrounding bundle sheath cells. There, the C4 acid is decarboxylated to release CO2 in a concentrated, localised pocket, and this CO2 is fixed again -- this time by RuBisCO -- entering the standard Calvin cycle (C3 cycle) to ultimately produce sugars/starch. The mesophyll cells only perform the initial CO2-tra …

Maize fixes CO₂ by the C4 pathway → (c).

• C4 plants (maize, sugarcane, sorghum, amaranthus) show Kranz anatomy and the first stable product of CO₂ fixation is the 4-carbon oxaloacetic acid. …

PEP (phosphoenolpyruvate) is the CO₂-accepting molecule in C₄ plants; RuBP plays that role only in C₃ plants.

C₄ plants (e.g., maize, sugarcane) fix atmospheric CO₂ in their mesophyll cells using the enzyme PEP carboxylase, which has a very high affinity for CO₂ and no oxygenase activity. It combines CO₂ with the 3-carbon compound phosphoenolpyruvate (PEP) to produce oxaloacetic acid (OAA), a 4-carbon compound — this is why the pathway is called the C₄ pathway. OAA is subsequently converted to malate/aspartate and shuttled into the bundle sheath cells, where CO₂ is released again and fixed a second time by RuBisCO in the standard Calvin cycle.

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The first stable product of CO2 fixation in a C4 plant is the 4-carbon acid OAA (oxaloacetic acid).

In C4 plants, CO2 is first fixed in the mesophyll cells. The primary CO2 acceptor is phosphoenolpyruvate (PEP), a 3-carbon compound, and the enzyme PEP carboxylase (PEPcase) catalyses the reaction. The addition of CO2 to PEP produces a 4-carbon organic acid, oxaloacetic acid (OAA). Because the first stable product has four carbon atoms, the pathway is called the C4 pathway. (Among th …