Question 1

The primary CO₂ acceptor in C4 plants (mesophyll cells) is ______, and the first product is ______:

Accepted Answer

PEP; oxaloacetic acid (OAA). C4 plants fix CO₂ first via PEP carboxylase into OAA (4-carbon) in mesophyll cells.

Question 2

C4 plants (e.g. maize, sugarcane) possess a special leaf anatomy called:

Accepted Answer

Kranz anatomy. Kranz ("wreath") anatomy features chloroplast-rich bundle sheath cells around the veins.

Question 3

In C4 plants the Calvin cycle operates in the ______ cells, which receive CO₂ released from a 4-carbon acid:

Accepted Answer

Bundle sheath. The 4-C acid moves to bundle sheath cells and releases CO₂ there, concentrating it for RuBisCO.

Question 4

Photorespiration occurs because RuBisCO also acts as an ______, especially at ______:

Accepted Answer

Oxygenase; high O₂/low CO₂. When O₂ is high and CO₂ low, RuBisCO oxygenates RuBP, starting photorespiration (loss of fixed carbon).

Question 5

C4 plants have negligible photorespiration because:

Accepted Answer

The bundle sheath maintains a high CO₂ concentration around RuBisCO. By pumping CO₂ into bundle sheath cells, C4 plants keep RuBisCO carboxylating, suppressing its oxygenase activity.

Question 6

Photorespiration is considered a wasteful process because it:

Accepted Answer

Consumes O₂ and releases CO₂ without producing ATP or NADPH (or sugar). Unlike normal respiration, photorespiration yields no ATP/NADPH and results in a net loss of previously fixed carbon.

C4 Pathway & Photorespiration — NEET Biology MCQs with Solutions

Questions with solutions