Question

Photorespiration does not occur in $C_4$ plants because

• A. of enzyme RuBisCO
• B. the first primary acceptor is phosphoenolpyruvate
• C. they do not require $C{O}_2$
• D. they have a mechanism that increases the concentration of $C{O}_2$ at the enzyme site

Answer 1

The correct option is D they have a mechanism that increases the concentration of $C{O}_2$ at the enzyme site

Photorespiration does not occur in $C_4$ plants because they have a mechanism that increases the concentration of $C{O}_2$ at the enzyme site. In the $C_4$ pathway, carbon fixation ultimately results in the production of malic acid in the mesophyll cells. The malic acid is broken down in the bundle sheath to release $C{O}_2$. Since the bundle sheath cells have thick walls they do not allow $C{O}_2$ to escape. This results in an increase in intracellular concentration of $C{O}_2$. This ensures that the RuBisCO in the bundle sheath cells functions as a carboxylase and not oxygenase, thus preventing photorespiration.