4. An egg that has been fertilized by a sperm cell is a
A. gonad.
B. fetus.
C. zygote.
D. gamete.
C
Look up the words you don't know (or read your text materials).
http://www.merriam-webster.com/dictionary
To determine the correct answer, let's break down the options and analyze them:
A. Gonad: A gonad refers to the sex organs that produce gametes (reproductive cells) and hormones. This is not the appropriate term for a fertilized egg.
B. Fetus: A fetus is the stage of development after the embryonic stage, which occurs several weeks after fertilization. Therefore, a fertilized egg is not yet a fetus.
C. Zygote: A zygote is the correct term for a fertilized egg, which is the product of the fusion of an egg cell and a sperm cell during fertilization. This newly formed cell has a complete set of chromosomes from both parents and marks the first stage of embryonic development.
D. Gamete: A gamete is a reproductive cell such as an egg or a sperm. While fertilization involves the fusion of gametes (egg and sperm), the resulting product is no longer considered a gamete.
Based on the explanations above, the correct answer is C. zygote.