List the three common structures of a protist, animal, and plant cell

Protist, animal, and plant are all eukaryotic cells and thus they all contain a nucleus and other membrane-bound organelles in them

Three structures which are common in potist, animal, and plant cell are:

Cell membrane: It is usually a lipid bilayer structure which separates the cellular content from the surrounding environment.

Nucleus: It is double membrane-bound organelle present in all eukaryotic cells. It contains the genetic material of the cell.

Ribosome: It is a small particle made up of RNA and protein. It is generally present in multiple numbers in the cytoplasm of all living cells. It provides the site for protein synthesis.

"do a testcross with a homozygous recessive plant."

several tissues working together form an organ, and several organs together make up an organisms.

the group of cell that carries out special jobs are tissue.