Mitotic cell divisions of a zygote lead to the formation of a fluid-filled ball of cells called a blastula.
a. true
b. false

True

Explanation:

The embryonic development of fertilized egg includes cleavage, blastulation, implantation, gastrulation and organogenesis.

Cleavage division divides the zygote into blastomeres. First cleavage division result in two blastomeres, second cleavage division results in a transient three cell stage. Third cleavage division forms 8 blastomere. These result in the formation of a sold ball of cells called morula. Morula is 16 cell stage and it descends towards the uterus in 4-6 days. As the morula enters the uterus, it gets a rich supply of nutrients. Trophoblast cells are formed which secrete a fluid into the interior creating a cavity called blastocoel. The inner cell mass now comes to lie on one side as embryonal knob. With the formation of blastocoel, morula is converted into blastula which is called blastocyst in mammals.

the trilobite is used as an index fossil for various geologic time periods as specific types of the trilobites were present in different geological time periods. they are a group of marine arthropods belonging to the class of trilobita.

explanation: