Question

The process which makes major difference between $\mathop C\nolimits_3$ and $\mathop C\nolimits_4$ plants is
(A) Respiration
(B) Glycolysis
(C) Calvin cycle
(D) Photorespiration

Answer 1

Melvin Calvin uses radioactive $\mathop {14}\nolimits_C$ 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. $\mathop C\nolimits_4$ is also known as the Hatch – slack pathway. This cycle is performed by plants that are adapted to dry tropical regions as that of sugarcane.

Complete answer:
$\mathop C\nolimits_4$ 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 a lack of process that is known as photorespiration. This process is exhibited by $\mathop C\nolimits_3$
The $\mathop C\nolimits_4$ plants have mechanisms that increase concentration of $\mathop {CO}\nolimits_2$ at the enzyme site and due to this they lack photorespiration.
Now let us match this process with the options given :-
Respiration:- this is a common process that occurs in both types of processes . Hence, this option is not correct.
Glycolysis:- it is the first step of respiration which involves conversion of glucose into pyruvate in both the plants . Thus this option is not correct.
Calvin cycle :- $\mathop C\nolimits_3$ cycle is also known as Calvin cycle . It is not a process. Thus, this option is not correct.
Photorespiration :- The $\mathop C\nolimits_4$ plants have mechanism that increase concentration of $\mathop {CO}\nolimits_2$ at the enzyme site and due to this they lack photorespiration but $\mathop C\nolimits_3$ plants possess it . Thus, this option is correct.

Our required answer is d that is photorespiration.

Note: Photorespiration is a process which involves loss of fixed carbon as $\mathop {CO}\nolimits_2$ 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.