Question

fill in the blanks to describe how the amount of yolk in the eggs vegetal pole leads to differences between species in the process and end result of cleavage. a sea urchin egg is microlecithal, meaning it contains little to no yolk. therefore, the animal and vegetal poles of sea urchin embryos divide synchronously, and the cells in the animal pole are smaller and more numerous than the cells in the vegetal pole of the blastula. a frog egg is mesolecithal, meaning it contains a moderate amount of yolk. therefore, the animal and vegetal poles of frog embryos divide asynchronously, and the cells in the animal pole are more numerous and smaller than the cells in the vegetal pole of the blastula. a chicken egg is hyperlecithal, and has so much yolk in the vegetal pole that cleavage is complete, which means that the cells in the vegetal pole of the egg dont even divide.

Explanation:

Eggs are classified based on yolk - amount as microlecithal (little to no yolk like sea urchin eggs), mesolecithal (moderate yolk like frog eggs), and hyperlecithal (a lot of yolk like chicken eggs). Yolk amount affects cleavage. In microlecithal eggs, poles divide synchronously with smaller and more numerous animal - pole cells. In mesolecithal eggs, poles divide asynchronously with more numerous and smaller animal - pole cells. In hyperlecithal eggs, much yolk in vegetal pole causes incomplete cleavage with non - dividing vegetal - pole cells.

Answer:

A sea urchin egg is microlecithal, meaning it contains little to no yolk. Therefore, the animal and vegetal poles of sea urchin embryos divide synchronously, and the cells in the animal pole are smaller and more numerous than the cells in the vegetal pole of the blastula.
A frog egg is mesolecithal, meaning it contains a moderate amount of yolk. Therefore, the animal and vegetal poles of frog embryos divide asynchronously, and the cells in the animal pole are more numerous and smaller than the cells in the vegetal pole of the blastula.
A chicken egg is hyperlecithal, and has so much yolk in the vegetal pole that cleavage is incomplete, which means that the cells in the vegetal pole of the egg don't even divide.