Question

Double fertilization occurs in: ____.

• A. Gymnocarpous (Gymnosperms)
• B. Angiosperms
• C. Bryophytes
• D. Algae

Hint:

Keep the chromosome ploidy straight: the Zygote is Diploid ($2n$), but the product of triple fusion, the Endosperm, is Triploid ($3n$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Double fertilization is a complex, unique reproductive mechanism discovered by S.G. Nawaschin, serving as a defining characteristic of flowering plants.

Step 2: Detailed Explanation:
In Angiosperms, the pollen tube releases two male gametes into the embryo sac:
• Syngamy: One male gamete fuses with the egg cell to form a diploid ($2n$) zygote, which eventually develops into the embryo.
• Triple Fusion: The second male gamete fuses with the two polar nuclei (or the secondary nucleus) to form a triploid ($3n$) Primary Endosperm Nucleus (PEN), which develops into nutritive endosperm tissue. Because two types of fusions take place inside the same embryo sac, the event is called double fertilization. Other plant groups like Gymnosperms, Bryophytes, and Algae do not show this phenomenon.

Step 3: Final Answer:
Double fertilization occurs exclusively in Angiosperms.

Answer 2

The question asks in which plant group double fertilisation takes place, so each option is checked for whether it shows this particular reproductive event.

1. Gymnosperms: Gymnosperms undergo a single fertilisation event, where one male gamete fuses with the egg to form the zygote. Their seeds develop nutritive tissue directly from gametophyte tissue that formed before fertilisation, without any second fusion event.
2. Angiosperms: Here, the pollen tube delivers two male gametes into the embryo sac. One fuses with the egg cell (syngamy) to form the diploid zygote, while the second fuses with the two polar nuclei (triple fusion) to form the triploid endosperm nucleus, which develops into nutritive tissue for the embryo. Because two separate fusion events happen together inside the same embryo sac, this is called double fertilisation, and it happens only in angiosperms.
3. Bryophytes: Fertilisation here involves a single motile male gamete swimming through a film of water to fuse with the egg, with no second fusion event and no endosperm formed afterward.
4. Algae: Many algae reproduce through a simple fusion of two gametes to form a zygote, again a single fusion event with no counterpart nutritive-tissue-forming step.

Only angiosperms show the two simultaneous fusion events, syngamy and triple fusion, that together define double fertilisation.

Therefore, the correct answer is Angiosperms.