Question Video: Recalling the Life Cycle of a Fern Biology

Video Transcript

During the life cycle of the ornamental fern, Polypodium, a zygote is produced. What plant form does it develop into? (A) A haploid gametophyte, (B) a haploid sporangium, (C) a haploid sporophyte, (D) a diploid sporophyte, or (E) a diploid gametophyte.

This question asks us about a multicellular organism, the ornamental fern, Polypodium, that reproduces through alternation of generations. Alternation of generations is an interesting phenomenon, whereby an individual organism alternates between two distinct forms: usually sexual and asexual, or haploid and diploid, within its own reproductive life cycle. Let’s review the life cycle of ferns so that we can work out the plant form that a zygote produced by these ferns develops into.

A mature fern is also called a sporophyte and is composed entirely of diploid cells. Remember, diploid means that the cells contain two complete sets of chromosomes, one set from each biological parent, which is often represented as 2n. The underside of fern leaves often contain spot-like structures called sori. Each of the sori contains diploid cells called spore mother cells. Spore mother cells undergo meiosis to produce haploid spores, which are stored in a structure called a sporangium. Remember, a haploid cell, which is often represented as n, contains only one set of chromosomes, half the number of most other body cells.

Haploid spores are eventually released from the sporangium and those that land on a suitable surface begin to grow. These spores grow into small plants called gametophytes, which are full of haploid cells. Gametophytes are responsible for the production of sex cells, or gametes: the sperm cells and the egg cells. The sperm cells produced by one gametophyte can either fertilize the egg cell of the same plant or an adjacent plant to produce a diploid zygote. The zygote eventually develops into a mature sporophyte full of diploid cells, initiating the life cycle once more.

Now, we can answer this question correctly. The zygote that is produced in the life cycle of the ornamental fern develops into (D), a diploid sporophyte.