Question

Some bacteria live in the roots of plants like soybeans and peas. What is the role of these bacteria in the nitrogen cycle?

Answer 1

The answer is D.  We can't directly use the nitrogen from the air so we need the bacteria to change it into something that we can use.

Answer 2

The correct answer is (d) To convert free nitrogen into usable nitrogen.

The nitrogen present in the soil is not directly used by the bacteria. It can be used only when the nitrogen is converted into usable form. These bacteria convert  atmospheric nitrogen into ammonia, then nitrite which is then converted into nitrate. This nitrate is used by the roots of the plants like soybeans and peas. This is the role of bacteria present in the roots of the plant to convert atmospheric nitrogen into usable form that can be used by plants.