A fertilized egg cell is considered a:

• A. embryo
• B. blastocyst
• C. zygote
• D. gamete

Answer: (C)

Verified step by step guidance

1. Understand the definitions of the terms provided in the problem: A zygote is the single-celled organism formed immediately after the fertilization of an egg by a sperm. An embryo refers to the early developmental stage of a multicellular organism after the zygote undergoes cell division. A blastocyst is a structure formed in the early development of mammals, consisting of a hollow ball of cells. A gamete is a reproductive cell (sperm or egg) that combines during fertilization to form a zygote.
2. Identify the stage of development being described in the problem. A fertilized egg cell is the very first stage after the sperm and egg combine, which corresponds to the zygote stage.
3. Clarify why the other options are incorrect: An embryo is a later stage of development after the zygote undergoes multiple rounds of cell division. A blastocyst is a specific structure formed during the embryo stage. A gamete is not a fertilized cell but rather the individual reproductive cells before fertilization.
4. Relate the concept to the process of fertilization: Fertilization occurs when a sperm cell and an egg cell (gametes) combine to form a single-celled zygote. This zygote will then undergo mitotic divisions to develop into an embryo and later a blastocyst.
5. Conclude that the correct term for a fertilized egg cell is 'zygote,' as it represents the immediate result of fertilization before any cell division occurs.