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Question: ASSERTION: Heteroscopy and retention of female gametophyte are responsible for origin of seed habit ...

ASSERTION: Heteroscopy and retention of female gametophyte are responsible for origin of seed habit in Selaginella.
REASON: Psilotum is a living fossil
A. Both assertion and reason are correct and reason is the correct explanation for Assertion
B. Both Assertion and reason are correct but reason is not the correct explanation for assertion.
C. Assertion is correct but reason is incorrect
D. Both Assertion and reason are incorrect

Explanation

Solution

A living remnant of an ancient Devonian flora (due to its obvious resemblance to the fossil plant Rhynia), Psilotum was long called a 'fern ally'.

Complete Answer:
Heterospory is a condition where the same plant bears two types of spores. In size, these spores vary. The smaller is referred to as a microspore and the larger is referred to as a megaspore. To build the male gametophyte, the microspore germinates and the megaspore reseeds to create the female gametophyte.
Now, let us find the solution from the options-
- Genera such as Selaginella and Salvinia are classified as heterosporous, producing two types of spores, large and small spores.
- The megaspores and microspores, respectively, germinate and give birth to female and male gametophytes.
- For varying times, the female gametophytes in such plants are holding on the parent sporophytes. Inside the female gametophytes, the growth of the zygotes into young embryos takes place.
- This occurrence is a precursor to the seed behavior that is known to be a significant evolutionary step.
- Heterospory and female gametophyte preservation are also liable for the root of the seed behavior in Selaginella.
- Psilotum, however, is a living fossil.

Thus, the correct option is option (B) Both Assertion and reason are correct but reason is not the correct explanation for assertion.

Note: This megaspore preservation and germination inside the megasporangium ensures that the zygote is properly formed. The zygote transforms into a sporophyte in the future. The evolution of the habit of the seed is correlated with the retention of the megaspore.