Photosynthesis Question 66

66. As compared to a $C_3$ - plant, how many additional molecules of ATP are needed for net production of one molecule of hexose sugar by $C_4$ plants:

[2005]

(a) two

(b) $six$

(c) twelve

(d) zero

Show Answer

Answer : c

Hints & Solution

(c) In $C_4$ plants every $CO_2$ molecule has to be fixed twice, so these plants are needed more energy for the synthesis of hexose sugar molecules than $C_3$ plants in which $CO_2$ has to be fixed only once. 18 ATP molecules are required by $C_3$ plants for the synthesis of one molecule of hexose sugar while 30 ATP molecules are needed by the $C_4$ plants for the same. Thus $C_4$ plants have a need of 12 ATP molecules extra than $C_3$ plants for the synthesis of one molecule of hexose sugar.