Question

Phosphoenol pyruvate (PEP) $CO_2$, acceptor in
(A) $C_3$ and $C_4$ plants
(B) $C_3$plants
(C) $C_4$plants
(D) $C_2$plants

Answer 1

Melvin Calvin used radioactive $\mathop {14C}\nolimits_{}$ isotope in algal photosynthesis studies. This led to discovery that the first $\mathop {CO}\nolimits_2$ fixation product was a three-carbon organic acid so he named this cycle as $\mathop C\nolimits_3$ cycle. $\mathop C\nolimits_3$ is also known as Hatch – slack pathway. This cycle is performed by plants that are adapted to dry tropical regions as that of sugarcane.

Complete answer:
$C_4$ plants can tolerate saline conditions due to abnormal due to abundant occurrence of organic acids in them which lowers their water potential more than that of soil. They can tolerate high ranges of light intensities; high salinity ranges due to lack of process that is known as photorespiration. This process is exhibited by $C_3$.
The $C_3$ plants have mechanisms that increase concentration of $CO_2$ at the enzyme site and due to this they lack photorespiration.

Now let us match this process with the options given:
$C_3$ and $C_4$ plants : The primary acceptor in the $C_3$ cycle is three carbon compounds so named as $C_3$ cycle and in the $C_4$ cycle are four carbon compounds.
$C_3$ plants : The primary acceptor in $C_3$ cycle is three carbon compound that is PhosphoenolPyruvate $C_4$plants : The primary acceptor of $CO_2$ in $C_4$ type is four carbon compound that is oxalo Acetic acid.
(D) $C_2$ plants: in these plants photorespiration takes place.

Hence, the correct answer is option (C)

Note: Photorespiration is a process which involves loss of fixed carbon as $CO_2$ in plants in the presence of light. It is initiated in chloroplast. This process does not produce ATP and NADPH and is a wasteful process. This process occurs usually when there is high concentration of oxygen.