Question

Coralloid roots contain symbiotic cyanobacteria, which fix nitrogen and in association with root tissue, produce beneficial amino acids. Which of the gymnosperms exhibit this type of roots.
A. Cycas
B. Linus
C. Lycopodium
D. Dryopteris

Answer 1

The coralloid roots contain symbiotic cyanobacteria (blue-green algae), that fix nitrogen and, in association with root tissues, produce such beneficial amino acids as asparagine and citrulline. Coralloid roots help in nitrogen fixation.

Complete answer:
Cycas solely are the only gymnosperms that have developed a specialized root organ to host symbiotic bacteria. Their lateral roots develop into coralloid roots, a dichotomous and coral-like small cluster of roots typically grows above the ground that acquires symbiotic bacteria. In a natural habitat, coralloid roots usually appear in initial life stages of plants and in adults, they appear mainly in habitat with poor and inaccessible nutrients with a high concentration of salt and lowland forests.

So the right answer is A (Cycas).

Additional Information: Cycas is a genus of plants belonging to the Cycadophyta, which are not closely associated with any palms, ferns, trees or any other modern group of plants. The cycas is cylindrical and is surrounded by the persistent petiole stems. Most species of the Cycas form branched or unbranched trunks but however, in some species, the main trunk can be subterranean with the leaf crown appearing to arise directly from the ground. There are two varieties of leaves - foliage leaves and scaly leaves. The foliage leaves are pinnate or more rarely bipinnate and organized spirally, with thick and hard keratindose. They are for a temporary period and fall off leaving back leaf-bases. The articulated leaves have midrib but do not have secondary veins. The scaly leaves are persistent, brown in colour and are protective in function. Megasporophylls not gathered in cones. Pollination takes place by air.

Note:
The plant takes several years to grow, sexual reproduction takes place after ten years of exclusive vegetative growth which occurs by bulbils arising at the base of the trunk. At the end of the Cretaceous, when the non-avian dinosaurs became extinct, so did most of the cycas in the Northern Hemisphere.