The hollow collection of undifferentiated cells that occurs after fertilization and initial mitosis is called a

Blastula

Explanation:

This mass of cell – called blastomere- surrounds a fluid-filled cavity-blastocoele- formed in the very early stages of development of an embryo in animals, after fertilization and the formation of a zygote. Blastomere cells have high potency and can differentiate into any type of cell.

d) center of the mid-ocean ridge

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enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products