Question

Isomorphic alternation of generation is found in
A) Oedogonium
B) Chara
C) Vaucheria
D) Ectocarpus

Answer 1

Alternation of generations is defined as the alternation of multicellular diploid and haploid forms in the organism's life cycle, in spite of whether or not these forms are free-living.

Complete answer:
Alternation of generations which is also known as metagenesis is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta so as to have diverse haploid sexual and diploid asexual stages. In these groups a multicellular haploid gametophyte with n chromosomes alternates with a multicellular diploid sporophyte with 2n chromosomes, invented of n pairs. A grown up sporophyte produces haploid spores by the process of meiosis, a method which reduces the number of chromosomes to half, from 2n to n.

The haploid spores develop and grow into a haploid gametophyte. At maturity, the gametophyte produces gametes by mitosis, which does not modify the number of chromosomes. Two gametes originating from dissimilar organisms of the same species or from the same organism combine to produce a diploid zygote, which develops into a diploid sporophyte. This cycle from gametophyte to sporophyte is the means in which all land plants and many algae undergo sexual reproduction.

In some species, such as the alga Ulva lactuca, the diploid and haploid forms are definitely both free-living independent organisms, basically identical in form and therefore said to be isomorphic. The free-swimming, haploid gametes form a diploid zygote which germinates to a multicellular diploid sporophyte.

Ectocarpus is a genus of filamentous brown alga that is a form of organism for the genomics of multicellularity. Among probable model organisms in the brown algae, Ectocarpus was chosen for the comparatively small size of its mature thallus and the speed with which it completes its life cycle. Ectocarpus is generally brown alga. It is richly found all through the world in cold waters. A few of them occur in fresh waters. The plant grows close to rocks and stones along coasts.

Hence the correct answer is option (D) ectocarpus.
Note: So we can conclude that the isomorphic alternation of generation is mainly found in ectocarpus which is a filamentous brown algae. These are generally found in cold waters.The sporophyte produces free-swimming haploid spores by meiosis that germinate into haploid gametophytes.