Question

Rhizoids in Riccia are
(a)Unicellular smooth-walled
(b)Unicellular tuberculate
(c)Both smooth-walled and tuberculate unicellular
(d)Multi-cellular smooth-walled and tuberculate

Answer 1

Hint: Rhizoids are a filamentous outgrowth similar to root hairs in structure. Riccia belongs to class Hepaticopsida under phylum Bryophyta. Unique types of rhizoids are seen in the different classes of Bryophytes.

Complete answer:
Hint: Rhizoids are a filamentous outgrowth similar to root hairs in structure. Riccia belongs to class Hepaticopsida under phylum Bryophyta. Unique types of rhizoids are seen in the different classes of Bryophytes.
Rhizoids occur as protuberances extending from the lower epidermal cells in bryophytes and algae. They are similar in structure and function to the root hairs present in vascular terrestrial plants. Similar structures are sometimes found in some fungi too.
These rhizoids may be seen as unicellular or multicellular structures.
In Riccia however, rhizoids are unicellular and unbranched structures. They anchor the thallus of the plant to the substrate and usually are of two types, smooth-walled and tuberculated.
These rhizoids are present in the mid-rib region of the thallus.

Additional Information:
 Riccia species include small and thalloid plants that are not differentiated into root, stem, and leaves.
The thallus is differentiated dorsoventrally with the upper or dorsal surface which is green and chlorophyll bearing, with a mid-dorsal sulcus or groove.
The lower or ventral surface has a mid-ventral ridge which bears scales that originate as a single row but later separate into two rows with the widening of the thallus. The scales are multicellular and are generally hyaline in appearance.
Rhizoids are seen in these plants and are of two types. One type is called smooth while the other type is called pegged or tuberculated rhizoids which help in anchorage and absorption. The inner surface of smooth rhizoids is smooth while tuberculate rhizoids have internal cell wall projections.
So, the answer is, ‘Both smooth-walled and tuberculate unicellular.’

Note:
 Rhizoids are generally seen in the terrestrial forms of Riccia only where they act as organs of anchorage. They are almost entirely lacking in aquatic forms of this plant.
In certain forms of algae, they have an extensive rhizoidal system that allows it to anchor itself to a sandy substrate which helps in absorbing the nutrients.
Free-floating microscopic species do not have rhizoids at all.