Question

Any two unicellular organisms which make the soil fertile.
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Answer 1

Answer:

rhisobium and fungus makes soil fertile and are unicellular.

Answer 2

Answer:

Rhizobium and the acetobacter are two unicellular organisms which make the soil fertile.

Explanation:

They live inside the 'root nodules' of some plants like soybean, bean, pea etc. They have the ability to absorb free nitrogen that they get from the air and convert it into the nitrogen compounds.  

A portion of 'fixed nitrogen' passes into the plant, a portion diffuses out in the surrounding soil and rest remains in the nodules. So the bacteria receive some amount of carbohydrates from the host plant.  

It is an example of symbiosis.

Addition of the nitrogen in the soil makes it fertile.