Question Video: Identifying the Number of Nuclei Which Are Not Involved in Double Fertilization | Nagwa Question Video: Identifying the Number of Nuclei Which Are Not Involved in Double Fertilization | Nagwa

Question Video: Identifying the Number of Nuclei Which Are Not Involved in Double Fertilization Biology • Third Year of Secondary School

How many of the eight haploid nuclei inside the embryo sac (female gametophyte) are not involved in double fertilization?

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Video Transcript

How many of the eight haploid nuclei inside the embryo sac, female gametophyte, are not involved in double fertilization?

This question is asking us about the process of double fertilization in a group of plants called angiosperms, which are commonly known as flowering plants. To understand this process, we first need to discuss the eight haploid nuclei that are found within the embryo sac in the ovule of an angiosperm. The egg cell is the female gamete in an angiosperm which contains a haploid nucleus. This and the seven other haploid nuclei in the embryo sac are formed from large diploid cells called spore mother cells through a special type of cell division called meiosis, which occurs within each ovule. This meiotic division of the spore mother cell produces four haploid cells called megaspores, three of which degenerate, while the fourth grows into a structure called the embryo sac.

The haploid megaspore within the embryo sac then divides by mitosis three times to produce the eight haploid nuclei that are mentioned in the question. Two of these haploid nuclei, which are now called the polar nuclei, move to the center of the embryo sac, forming one large central cell. The other six nuclei move to opposite ends of the embryo sac and become independent cells. The three cells furthest from the micropyle are called antipodal cells. The cell shown closest to the micropyle at the other end of the embryo sac grows and develops into an egg cell, while the two cells either side of it develop into cells called synergids.

Now, we are ready to discuss which of these eight haploid nuclei are involved in double fertilization. It is called double fertilization as it involves two major fertilization events. One of the two haploid male sperm cells fuses with the haploid egg cell to produce a diploid zygote. The zygote then divides by mitosis several times to form an embryo. The synergid nuclei are theorized to aid this fertilization event but are not directly involved in fertilization itself.

The other haploid male sperm nucleus fuses with the two haploid polar nuclei in the center of the embryo sac, which forms the triploid endosperm nucleus. Of the eight haploid nuclei, three, the two polar nuclei and the egg cell nucleus, are involved in double fertilization. You can identify these nuclei as the orange dots within the ovule. However, the question is asking about the number of haploid nuclei that are not involved in double fertilization, which are the three antipodal cells and two synergid cells shown in the ovule as the pink dots.

Therefore, the number of haploid nuclei in the embryo sac that are not involved in double fertilization is five.

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