Solution:

• Hatch slack pathway- In C4 plants the process is called the Hatch & Slack Pathway, the glucose synthesis process. The Calvin Cycle is followed by every photosynthetic plant, although certain plants have a primary step known as the C4 pathway. The C4 route is widely followed by plants in tropical desert environments. The initial result of carbon fixation is oxalo-acetic acid (OAA), a four-carbon molecule. Such plants are unique and have specific adaptations. Phosphoenolpyruvate (PEP), a 3-carbon molecule, is the starting point for the C4 pathway. This is the major CO2 acceptor, and carboxylation is carried out by an enzyme known as PEP carboxylase. They produce oxalo-acetic acid, a 4-carbon compound (OAA). It is eventually transformed into malic acid, another 4-carbon molecule. They are then transported from mesophyll to bundle sheath cells. OAA is broken down in this step to produce carbon dioxide and a 3-C molecule. The CO2 produced is used in the Calvin cycle, while the 3-C molecule is returned to mesophyll cells for PEP regeneration.

• Calvin cycle – The Calvin cycle is also known as the C3 cycle, or the dark or light-independent photosynthetic reaction. It is, however, most active during the day, when NADPH and ATP levels are high. Plant cells utilise basic resources provided by light reactions to construct organic molecules:

1. The endergonic reactions are driven by ATP, which is produced through cyclic and noncyclic photophosphorylation.

2. NADPH, which is produced by photosystem I, is a source of hydrogen as well as the energetic electrons needed to attach it to carbon atoms. The energy-rich C—H bonds of sugars absorb a large portion of the light energy captured during photosynthesis. Steps leading to the formation of carbohydrates following the division of the water molecule. This happens cyclically and is called the Calvin Cycle.

(c) PEP carboxylase– PEP carboxylation is the first enzyme in the C4 or Hatch Slack pathway’s carbon fixing. It catalyzes the conversion of phosphoenolpyruvate (PEP) to oxaloacetic acid (OAA), the 4C acid, by adding CO2. It is present in mesophyll cells of C4 plants. The C4 cycle, the CAM cycle, and the Citric Acid Cycle biosynthetic flux are the three most essential roles that PEP carboxylase performs in plant and microbial metabolism.

1. C4 Cycle Some plants use a process known as the C4 Cycle to increase the local CO2 content. In the mesophyll tissue, PEP carboxylase is responsible for binding CO2 and converting it to oxaloacetate.
2. The CAM cycle is frequent in species that live in arid environments. Plants take in CO2 at night by fixing it with PEP and converting it to oxalate via PEP carboxylase. These are transformed and stored for usage throughout the day, when light-dependent processes generate energy and reducing equivalents like NADPH, which are used to drive the Calvin cycle.
3. Citric Acid Cycle- In non-photosynthetic metabolic processes, PEP carboxylase plays a key role. In the Kreb’s cycle, PEP carboxylase resupplies oxaloacetate. Some PEP is converted to oxaloacetate by PEP carboxylase in order to boost flow through the cycle. Increased flux is critical for the production of numerous compounds because the citric acid cycle intermediates serve as a centre for metabolism.

(d) Bundle sheath cells – A layer or area of densely packed cells that surround a plant’s vascular bundle. The bundle sheaths control the flow of chemicals between the vascular tissue and the parenchyma, as well as protecting the vascular tissue from air exposure in leaves.

Photosynthetic cells placed in a tightly packed sheath surrounding a leaf vein are known as bundle-sheath cells. It is made up of one or more cell layers, usually parenchyma, and creates a protective covering on leaf veins. Between the bundle sheath and the leaf surface are loosely organized mesophyll cells.  The specialized sclerenchyma cells present around vascular bundles in the veins of C4 plants are called bundle sheath cells.