Question

Apogeotropic roots in Cycas look like corals of anthozoans (coelenterata) showing mutual association with
A. Cyanobacteria
B. Bacteria
C. Fungi
D. Obligate parasite

Answer 1

Hint: Facultative symbiosis is a relationship in which two different organisms benefit from one another by living in close association. In apogeotropic roots in Cycas, this kind of relationship is seen.

Complete answer:
The apogeotropic roots are positively geotropic roots which grow upward towards the surface of the soil and look like anthozoans. These are pre coralloid roots which develop special symbiotic organs at an early age.

Option A: Cyanobacteria are free living bacteria that have the ability to fix the nitrogen present in the atmosphere. They live in symbiotic association with Cycas where Cycas provide them with fixed carbon and stable environment in exchange with fixed nitrogen. Therefore, this is the correct option.

Option B: Bacteria are found in a symbiotic relationship with the host organism’s stomach for food digestion. Therefore, this is the incorrect option.

Option C: Fungi like mycorrhizae are involved in symbiotic relationships with lichen in which they mutually benefit from one another. Therefore, this is the incorrect option.

Option D: Obligate parasites are those that live on other organisms and cause them harm for their own benefit. Therefore, this is the incorrect option.

Thus, the correct option is A) Cyanobacteria.

Additional information:
- Cyanobacteria uses the nitrogenase enzyme to fix the atmospheric nitrogen.
- The complex process of nitrogen fixation is a key feature of the relationship between cyanobacteria and cycas.

Note: Symbiotic relationship between the cyanobacteria and cycas is based on exchange of nutrients between them in which both the organisms put their efforts to thrive.