Question

Which of the following is the importance of molybdenum in plant metabolism?
(a)Carbon assimilation
(b)Nitrate reduction
(c)Plant breeding
(d)Chromosome contraction

Answer 1

The importance of molybdenum in plant metabolism is that it makes up an enzyme known as nitrogenase which is basically a Mo-Fe protein. The enzyme nitrogenase is responsible for nitrogen fixation.

Complete answer:
The importance of molybdenum in plant metabolism is that it is involved in nitrogen metabolisms like nitrate reduction and nitrogen fixation. Molybdenum is a micronutrient which means that it is required by the plant in small quantities like less than 10 mmole ${ Kg }^{ -1 }$. It is absorbed in the form of molybdate ions ${ MoO }^{ 2+ }$. The deficiency of Mo can result in the delay of flowering. It is found in the enzyme nitrogenase which is found in the root nodules of leguminous plants. This enzyme along with leghaemoglobin is responsible for converting atmospheric nitrogen to ammonia (nitrogen fixation).

Additional Information: Let us look in detail at the functioning of the enzyme nitrogenase.
-The enzyme nitrogenase is highly sensitive to molecular oxygen and thus requires anaerobic conditions to function or it will become denatured.
-These anaerobic conditions are provided by the enzyme leghaemoglobin which is an oxygen scavenger.
-The microbes usually live as aerobes under free-living conditions but become anaerobic during symbiotic association so as to allow nitrogenase to function.
-The enzyme nitrogenase traps ${ N }_{ 2 }$ and causes a reduction of it until 2 molecules of ${ N }H_{ 3 }$ are formed.
-This process requires a high input of energy of 16 ATP which is provided by the host i.e. plant cells.
The equation is as follows:
${ N }_{ 2 }\quad +\quad { 8e }^{ - }\quad +\quad { 8H }^{ + }\quad +\quad 16ATP\xrightarrow { \quad \quad \quad \quad \quad \quad } { 2NH }_{ 3 }\quad +\quad { H }_{ 2 }\quad +\quad 16ADP\quad +\quad { 16P }_{ i }$
So, the correct option is ‘Nitrate reduction’.

Note: -The other micronutrients include iron, manganese, copper, zinc, boron, chlorine, and nickel.
-Macronutrients are nutrients that are required by plants in large amounts such as more than 10mmole ${ Kg }^{ -1 }$.
-Macronutrients include carbon, hydrogen, oxygen, nitrogen, potassium, phosphorus, sulfur, calcium, and magnesium.