Final answer:
The correct sentence completion indicates that an egg is a heterogeneous mixture, with cleavage types in development varying based on yolk content; total cleavage occurs with minimal yolk, while partial cleavage with significant yolk.
Step-by-step explanation:
The sentence that completes the following question correctly is: "If, when an egg is broken, its yolk and white separate, then you know it is a heterogeneous mixture." This indicates that an egg contains different substances that can be visibly distinguished from one another, with varying compositions between the yolk and the egg white.
In terms of embryonic development, total cleavage takes place in eggs having little or no yolk, which allows for the even distribution and division of cells, whereas partial cleavage occurs in eggs that have a large amount of yolk. The yolk serves as a food source for the developing embryo, particularly in very yolky eggs of vertebrates, where the embryonic layer forms on the surface of the yolk.