would you please explain the C4 cycle in a simple way
C4 pathway is a highly efficient and advanced pathway for carbon dioxide assimilation in C4 plants. C4 plants have a special type of leaf anatomy, called Kranz anatomy and the cycle occurs in two types of cells; Bundle sheath cells and Mesophyll cells.
It is called C4 cycle because the first fixation product formed in this cycle is a four carbon compound oxaloacetic acid. The cycle is as follows ;
Step 1 : Fixation of CO2 in mesophyll cells.
Here, CO2 from the atmosphere is taken up by the mesophyll cells and combined with Phosphoenol pyruvate (PEP) to form Oxaloacetic acid which is then converted to another C4 compound .
Step 2: C4 compound is transferred to bundle sheath cells.
Step 3: Decarboxylation of C4 compound in bundle sheath cells.
The C4 compound which was transported is decarboxylated (CO2 is removed) to form a three carbon compound (C3 acid). CO2 is released inside the bundle sheath cell and is used for normal calvin cycle.
Step 4: Transfer of C3 acid to the mesophyll cells.
Step 5 : Regeneration of PEP from C3 acid in mesophyll cells.
Image Source : Class XI Biology NCERT, Page 219
This cycle is free from photorespiration as mesophyll cells do not have RUBisCo enzyme. Carbon dioxide is specifically transferred to the bundle sheath cells so that carbon fixation can occur there via calvin cycle.