Question

differentiation in the zygote occurs when:
○ sperm and ovum meet.
○ the combined material from both gametes meshes together.
○ the zygote reaches the four-cell stage.
○ cells begin to specialize.

Explanation:

To solve this, we analyze each option:

• "sperm and ovum meet" is fertilization, not differentiation.
• "the combined material from both gametes meshes together" is part of fertilization/zygote formation, not differentiation.
• "the zygote reaches the four - cell stage" is just a stage of cell division, not differentiation.
• Differentiation in a zygote is defined as cells beginning to specialize (take on specific functions and structures).

Answer:

D. cells begin to specialize.