OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What is a zygote?

1. A fertilized egg

2. A developing embryo

3. A sperm cell

4. An unfertilized egg

The correct answer is: A fertilized egg

A zygote is defined as a fertilized egg, which is the initial cell formed when a sperm cell successfully fertilizes an egg cell. This process marks the beginning of sexual reproduction in many organisms. After fertilization, the zygote undergoes a series of cell divisions and developmental stages, eventually leading to the formation of an embryo. This is the critical first step in the process of development, as the zygote contains genetic material from both parents, contributing to the genetic uniqueness of the organism. The term zygote specifically refers to this earliest stage and does not apply to other stages of development, such as a developing embryo which comes after the zygote has divided and differentiated into more complex structures. A sperm cell and an unfertilized egg are distinct entities that have not yet united to form a zygote. Thus, understanding that a zygote is specifically a fertilized egg is essential for grasping concepts in reproductive biology.