Which of the following organelles is not present in an animal cell? a. Nucleus, b. Cell membrane, c. Cell wall, d. Centriole.

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A nucleus is present in all eukaryotic cells and absent in prokaryotic cells. Animals are eukaryotic, thus animal cells have nuclei (an exception to this rule is red blood cells, who lose their nuclei in order to have room to carry more hemoglobin). 

All cells have cell membranes. The membrane is what keeps the cell interior separate from the rest of the surrounding environment. 

Some cells are surrounded by a cell wall. The wall is located outside the cell membrane and provides support and protection. All plant cells have cell walls. Animal cells do not have cell walls. 

Centrioles are structures which aid the cell skeleton during the process of division. All animals and some plants have centrioles. 

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