All multicellular organisms begin as a single cel. Within four or five days, that first cell multiplies into a ball-like structure of about 100 cells. What is this structure called?​

The right answer is a blastocyst.

The blastocyst Stage of embryo development is characterized by the formation in the center of the morula (embryonic cell group) of a cavity isolated from the external environment: the blastocoel.

In embryonic development, this step precedes gastrulation.

Blastocysts are indeed composed of a hundred cells; they have the shape of a hollow sphere at the bottom of which is the mound of the "embryonic bud" from which the embryonic stem cells are derived

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.

voluntary muscles are controlled by the cerebellum.