Question

The juvenile stage of the gametophyte of moss is
A. Green, filamentous and branched structure called protonema
B. A tetra flagellate body
C. Dorsoventrally flattened plate like body
D. A colourless mass of tubular structures

Answer 1

Hint: The juvenile stage can be defined as one of the phases of body growth which falls in between birth and reproductive maturation of the organism. In plants this phase is followed by the reproductive phase (reproductive maturity).

Complete Answer
The organism exhibiting sexual mode of reproduction, is called gametophyte whereas that exhibiting asexual mode of reproduction is called sporophyte.
In the question given above, we are concerned with the juvenile stage of the gametophyte of moss. Let's study this concept in a bit detail to find the correct answer.
While growing through an asexual mode of reproduction, Mosses reproduce through spores. These spores are single celled structures that are capable of growing into an independent individual. Multiple spores tightly packed inside a brown colored capsule, start growing on the body of the parent organism. These spores take some time to grow and mature, which is called their juvenile stage. Soon after attainment of vegetative stage that includes maturation of these spores, the brown capsule bursts off to release them. Therefore, such an organism is called sporophyte.
However, when the organism switches to sexual mode of reproduction, it is referred to as gametophyte, as it starts producing diploid gametes. In case of Mosses, the spores attain a green, filamentous and branched structure called protonema that represents a juvenile stage of moss gametes. After maturation they follow their conventional sexual reproduction pattern.

Therefore, we can say that option C is the correct answer.

Note:
Certain plants (like liverworts) and algae (like Spirogyra) are found to omit natural phenomena called alternation of generation. Under this phenomenon, these organisms while following asexual mode of reproduction since ages but suddenly switch to sexual mode of reproduction in order to improve species health.