Question:

Given below are two statements: One labelled as Assertion A and the other labelled as Reason R:
Assertion A: The first stage of gametophyte in the life cycle of moss is protonema stage.
Reason R: Protonema develops directly from spores produced in capsule.
In the light of the above statements, choose the most appropriate answer from the options given below:

Updated On: Jul 25, 2024
  • Both A and R are correct but R is not the correct explanation of A
  • A is correct but R is not correct
  • A is not correct but R is correct
  • Both A and R are correct and R is correct explanation of A
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The Correct Option is D

Approach Solution - 1

The given assertion and its reason are both correct, as gametophytes in the moss life cycle undergo 3 stages that are:

  • SPORE \(\rightarrow\) protonema \(\rightarrow\) gametophyte plant body.
  • First, the spore converts into a protonema, which is a thread-like structure; after that, it matures to form mature gametophytes.

So, the correct option is (A): Both A and R are correct and R is correct explanation of A.

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Approach Solution -2

The protonema stage is indeed the first stage of the gametophyte in the life cycle of mosses. Additionally, protonema does develop directly from spores produced in the capsule, supporting Assertion A. Therefore, Reason R explains why Assertion A is true.

So, the correct option is (A): Both A and R are correct and R is correct explanation of A.

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Concepts Used:

Bryophytes

Bryophyta is a taxonomic division under Kingdom Plantae comprising of three non-vascular land plants namely:

  • Liverwarts
  • Hornwarts 
  • Mosses

Characteristics of Bryophytes:

  • Plants in this category do not have roots but have crude stems and leaves.
  • They have “rhizoids” instead of roots which helps the plant to anchor to surface.
  • These roots or rhizoids do not absorb nutrients like other usual plant roots.
  • Mosses release spores from their leaves which travels by water and make new mosses in new locations.
  • Water is very essential for mosses to grow and spread. They can entirely dry out and survive. When in contact with water, they again revive and continue growing.

Classification of Bryophytes:

According to the newest classification, Bryophyta is split into three classes:

Hepaticopsida (Liverworts): The classification of Bryophytes is incomplete without Hepaticopsida.

Anthocerotopsida (Hornworts): Containing more than 300 species, Anthocerotopsida exhibit the following salient features – 

  • Thallus shows no signs of scales.
  • The gametophytic body comprises of a thalloid, without any internal tissue differentiation.
  • Seta is meristematic.
  • Sporophyte is cylindrically shaped. It only partially depends on the gametophyte to derive its nutrition.

Bryopsida (Mosses): This class of Bryophytes contains nearly 1500 species, making it the largest class among the three. Also known as mosses, common examples of Bryopsida include polytrichum and funaria, among others.