Some of these terms/chemicals are associated with the $C_{4}$ cycle. Explain.
$(a)$ Hatch-Slack pathway
$(b)$ Calvin cycle
$(c)$ $PEP$ carboxylase
$(d)$ Bundle sheath cells

(A-D) Hatch-Slack pathway: The $C_{4}$ pathway is an alternative carbon fixation process found in certain plants. It was discovered by $M. D. Hatch$ and $C. R. Slack$,hence it is named the Hatch-Slack pathway.
$(b)$ Calvin cycle: In $C_{4}$ plants,the Calvin cycle occurs specifically within the bundle sheath cells. This is where $CO_{2}$ is finally fixed into glucose via the enzyme $RuBisCO$.
$(c)$ $PEP$ carboxylase: This is the primary $CO_{2}$ fixing enzyme found in the mesophyll cells of $C_{4}$ plants. It catalyzes the reaction between $CO_{2}$ and phosphoenolpyruvate $(PEP)$ to form the $4-C$ compound oxaloacetic acid $(OAA)$.
$(d)$ Bundle sheath cells: These are large,specialized parenchymatous cells arranged in layers around the vascular bundles of $C_{4}$ plant leaves. They contain large numbers of chloroplasts (often agranal) and are the site where the Calvin cycle takes place.