how many cell layers are found in a blastula?

There are three different layers of cells found in blastula.

Explanation:

The blastula is a ball of stem cells that are formed during the formation of a zygote, the cells that in the blastula get differentiated to form different organs and organ systems.

The first layer that is the ''ectoderm'' differentiates into the outer skin layers, the ''mesoderm'' differentiates into the soft tissues that is the connective tissues and the last layer ''endoderm'' modified into a lining that protects the internal organs such as the digestive system.  

a. to encourage apoptosis

oxygen = 21% of the atmosphere

nitrogen = 78%

carbon dioxide = 0.1%

argon =0.934%