Simplify the following text for a Grade 10 native English-speaking person.
Original: In other words , a single fertilized egg cell -- the zygote -- changes into the many cell types including neurons , muscle cells , epithelium , blood vessels etc. as it continues to divide .
Simplified: In other words , a single fertilized egg cell â `` the zygote â `` changes into the many cell types including neurons , muscle cells , epithelium , blood vessels etc. as it continues to divide .