Question

If the haploid no. of chromosomes in gymnosperm is 12, what will be no. of chromosomes in its root and endosperm?
A. 12,12
B. 12,24
C. 24,12
D. 24,36

Answer 1

The word gymnosperm means naked seeds. Gymnosperms are plants in which the ovules are not enclosed by the ovary wall and remain open and exposed, before and after fertilization. The seeds formed after fertilization are naked in gymnosperms. In gymnosperms, female and male gametophytes remain within the sporangia and are retained on the sporophytes. They do not have a free living existence.

Complete answer:
Gymnosperms are perennial, evergreen woody plants. They are known as sporophytes because they produce spores. Gymnosperms are heterosporous, that is they produce haploid microspores and megaspores. The sporophyte plant body of a gymnosperm has diploid (2n) condition. These microspores and megaspores develop to form the male and female gametophyte generations, respectively. The reduced male gametophyte is called the pollen grain, whose development takes place within the microsporangia. The megaspore mother cell is formed from the nucellus which is protected by an ovule. The megaspore mother cell produces 4 megaspores by meiotic division. One of the megaspores develop into a multicellular female gametophyte, which have more than one female sex organs. The nutrition required is stored in these female gametophyte cells which are haploid in condition. In gymnosperms, the female gametophyte cells with nutritive function are called primary endosperms. Different from angiosperms, the endosperm production happens before fertilisation in gymnosperms. Here the roots belong to the diploid sporophyte plant body and therefore contain 24 chromosomes (2n) and the endosperm which is haploid will contain 12 chromosomes (n).
So, the correct answer is “Option C”.

Note:
In angiosperms, endosperm production happens only if fertilization occurs. One of the sperms fuse with the polar cells to produce triploid primary endosperm condition (3n). But in gymnosperms, the female gametophyte cells become the primary endosperm, even without fertilization. All seed bearing plants, that is, angiosperms and gymnosperms follow a diplontic life cycle in which the diploid sporophyte is the dominant photosynthetic phase of the plant and the gametophyte phase is represented by haploid gametophytes.