Question

The coralloid roots in Cycas are
A. Aerial
B. Apogeotropic
C. Phototropic
D. Positively geotropic

Answer 1

Hint: These roots grow away from the earth and these roots harbor blue-green algae which helps in fixing nitrogen. They are an example of symbiotic association in nature.

Complete answer:
Cycas develop from the specialized organs which are called coralloid roots. Branching roots are of two kinds, one is branching geotropic roots and the other one is branching apogeotropic roots and these apogeotropic roots are referred to as coralloid roots.

These roots have Cyanobacteria which is blue-green algae, it helps in fixing nitrogen. These produce asparagine and citrulline which are beneficial amino acids produced in association with root tissues, these are apogeotropic in nature. Apogeotropic means that they grow away from the earth or you can say negative geotropism. These roots help cycas to form mutualistic and symbiotic relationships with blue-green algae.

> Option A which is Aerial then in cycas the coralloid roots are not aerial but instead of it they are apogeotropic. Therefore, this option is not the correct one and it gets eliminated.

> Option B which is apogeotropic, this option is the correct one. Apogeotropic means that they grow away from the earth or you can say it shows negative geotropism. Therefore, this option is the correct one.

> Option C which is phototropic. It is the growth of an organism in response to the light stimulus. But in cycas the growth is away from the earth i.e., they show negative geotropism. Therefore, this option is not the correct one and it gets eliminated.

> Option D which is positively geotropic. Positively geotropic means the growth is towards earth and negative means growth is away from the earth. Coralloid roots in cycas are not positively geotropic but they are negatively geotropic i.e., they grow away from the earth. Therefore, this option is not the correct one.

Hence, the correct answer is option (B).

Note: In association with root tissues these produce beneficial amino acids which are apogeotropic in nature. Therefore, Coralloid roots in cycas are apogeotropic since they grow away from the earth. These roots help cycas to form the mutualistic relationship with Cyanobacteria.