Question

$C_4$ plants have bundle sheath cells which possess

• A. few chloroplasts with thin walls so that gaseous exchange can take place
• B. large number of chloroplasts with thick walls impervious to gaseous exchange
• C. large number of chloroplasts and intercellular spaces
• D. few chloroplasts with thick walls and no intercellular spaces

Answer 1

Answer: (B)

$C_4$ plants often possess a characteristic leaf anatomy called kranz anatomy. They have dimorphic chloroplasts, i.e. two types of chloroplasts are present, those in mesophyll cells are different from the chloroplasts in bundle sheath cells with thick walls
The primary function of kranz anatomy is to provide a site in which $C{O}_2$ is first fixed in $PEP$ by $PEP$ case. This $C{O}_2$ is then released in bundle sheath cells and is fixed through Calvin cycle. In this manner, high concentration of $C{O}_2$ is maintained in bundle sheath cells, so that RuBisCO acts as carboxylase only and not oxygenase, thereby preventing photorespiration