Question

Assertion: The main plant body of bryophytes is a gametophyte.
 Reason: Alternation of generation is absent in bryophytes.
a. Both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
b. Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion.
c. Assertion is correct but Reason is incorrect.
d. Assertion is incorrect but reason is correct.

Answer 1

Hint:-Alteration of generation also termed as Metagenesis, is defined as the alteration of asexual phase and sexual phase in the lifecycle of an organism.

Complete step-by-step solution:-When we see the life cycle of the bryophytes, we find that their main plant body is haploid i.e. it produces gametes and it is known as gametophyte.
The male sex organ is called anthredium and the female sex organ is called archegonium. In bryophytes, the male gametes are motile and they are known as antherozoids. They are comma shaped and biflagellated. Female gamete is called an egg.
Looking into the life cycle of bryophytes gives us evidence that zygote is very short lived. The major portion of the life cycle consists of the haploid phase that is known as gametophytic phase.
Zygote is formed after the fusion of antherozoid and the egg. The newly formed zygote does not directly undergo meiosis (reduction division) to form spore, rather it first forms a diploid sporophyte.
Sporophyte then undergoes mitotic division to form spore mother cells. These spore mother cells then form spores by reduction division. The spores represent the gametophytic generation and the sporophyte or the spore mother cells represent the sporophyte generations.
Hence, the major portion of the life cycle in bryophytes consists of the haploid (gametophytic) phase but we cannot say that alternation of generation is absent in bryophytes because both haploid and diploid phases at present though the diploid phase is very much short lived.
Thus, Assertion is correct but Reason is incorrect.
Correct option is(c).



Note:-
- The sex organs are formed on gametophyte.
- Sex organs are multicellular and jacketed in bryophytes.
- In Bryophytes, sporophyte is dependent on gametophyte.