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

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What is the significance of stage 4 in embryonic development?

The cells have differentiated into muscle cells
The zygote is now referred to as an embryo with embryonic stem cells
The embryo has started to split into twins
The number of cells has decreased from 8 to 4

The correct answer is: The zygote is now referred to as an embryo with embryonic stem cells

Stage 4 in embryonic development marks a crucial transition where the zygote, after several rounds of cell division, is recognized as an embryo. This stage is significant because it signifies that the cells within the embryo are embryonic stem cells, which have the potential to differentiate into any type of cell in the body. This versatility is essential for the proper development of tissues and organs as the organism continues to grow. During earlier stages, particularly the initial cell divisions, the zygote begins to divide but has not yet achieved its identity as an embryo. The transition to being categorized as an embryo highlights the beginning of specialized processes that lead to further differentiation and development. Understanding this aspect of developmental biology is crucial, as these embryonic stem cells ultimately have a vital role in the formation of various tissues in the body.