Final answer:
The merging of a sperm cell and an ovum during fertilization results in a diploid zygote, which contains a full set of chromosomes and undergoes mitosis to develop into a multicellular organism.
Step-by-step explanation:
The result of the merging of a sperm cell and an ovum in fertilization is known as a zygote. This process is vital as it restores diploidy to the cell, ensuring that the offspring has a complete set of chromosomes. The sperm and ovum are both haploid cells, which means they each carry half of the necessary chromosomes. When these two gametes fuse, they create a diploid zygote containing the full set of chromosomes, half from each parent. In humans, this means the zygote will have 46 chromosomes, or 23 pairs. Following fertilization, the zygote undergoes multiple rounds of mitosis and begins to develop into a multicellular organism, ultimately implanting in the uterus.