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.
