Zygote Development and Reduction Division

A zygote is a diploid cell ($\(2n\)$) that is formed by the fusion of two haploid gametes (fertilization). Reduction division, also known as meiosis, is a type of cell division that reduces the number of chromosomes by half, producing haploid cells ($\(n\)$) from a diploid cell ($\(2n\)$).

In many organisms, the zygote may undergo meiosis immediately after formation, leading to the production of haploid individuals or cells. However, in plants and some algae, the zygote behaves differently.

Sporophyte: The Multicellular Body from Zygote

When a zygote does not undergo reduction division (meiosis) immediately, it means it undergoes mitotic divisions instead. Mitosis is a type of cell division that produces genetically identical diploid cells. Repeated mitotic divisions of the diploid zygote lead to the formation of a multicellular diploid body.

This multicellular diploid body, produced from the zygote through mitosis, is called a sporophyte.

Understanding the Options

• Sporophyte: This is the diploid ($\(2n\)$), multicellular stage in the life cycle of plants and some algae. It is formed from the zygote by mitotic divisions and produces spores through meiosis. This matches the description in the question.
• Gametophyte: This is typically the haploid ($\(n\)$), multicellular stage in the life cycle. It is formed from a spore and produces gametes (sperm and egg) through mitosis. It is not formed directly from the zygote.
• Antheridium: This is the male sex organ of the gametophyte, which produces male gametes (sperm). It is a part of the gametophyte stage, not the multicellular body formed from the zygote.
• Archegonium: This is the female sex organ of the gametophyte, which contains the egg cell. It is also a part of the gametophyte stage, not the multicellular body formed from the zygote.

Therefore, the multicellular body produced by a zygote that does not undergo reduction division immediately is the sporophyte.