Question

In Kranz anatomy, the bundle sheath cell have
A. Thick walls, many intercellular spaces and no chloroplasts
B. Thin walls, no intercellular spaces and large number of chloroplasts
C. Thick walls, no intercellular spaces and large number of chloroplasts
D. Thin walls, many intercellular spaces and several chloroplasts

Answer 1

Hint:-${C_4}$ plants make up $5\% $ of the green plants and their mechanism for photosynthesis is a recent phenomenon which facilitates faster $C{O_2}$ fixation. Here, photosynthesis occurs twice - in mesophyll and bundle sheath cells because of Kranz anatomy in their leaves.

Complete Answer:-Photorespiration is a redundant process that occurs in most photosynthetic plants during $C{O_2}$fixation. To avoid this, the adaptive evolution from the ubiquitous ancestral ${C_3}$ plants (Calvin cycle) to the ${C_4}$ plants (Hatch-Slack pathway) occurred. Common examples of ${C_4}$ plants are those that are acclimated to tropical dry and hot environments like maize, sugarcane and millet.

The entering $C{O_2}$is initially converted into a $4$ carbon oxaloacetate compound (hence${C_4}$) in the mesophyll cells and sent into the bundle sheath cells for the Calvin Cycle. The mesophylls are found skirted in a wreath-like manner around the bundle sheath cells that are, in turn, clustered around the central vascular core. This unique Kranz anatomy in the leaves of${C_4}$, enabling physical separation between the two reactions, is what renders this Hatch-Slack pathway possible.

Thus, the correct answer is option C. Thick walls, no intercellular spaces and a large number of chloroplasts.

Note:- The energy required for this process of Hatch Slack pathway-enabled photosynthesis is ATP expensive ($30$ ATP molecules). However, it remains cumulatively more useful than what is spent in ${C_3}$because of lesser photorespiration and lesser water loss (photosynthesis happens even when stomata are closed), which is why this mechanism is more efficient.