What structure keeps harmful chemicals out of animal cells?

Cell membrane protects animals cells from harmful chemicals.

Explanation:

The cell membrane is a tough covering composed of the phospholipids and proteins and forms a bilayer around the cells. This acts as a semi-permeable membrane and controls the transport of ions, organic molecules and solutes to and from the cell through selective permeability.

The hydrophilic and hydrophobic properties and the corresponding polarity of the cell membrane and ionization status of the chemicals prevent the entry of harmful substances into the cell. The cell membrane functions as a barrier system and prevents the flow.

"do a testcross with a homozygous recessive plant."

the offspring would all be white. if the parents are both white flowers then they have the genotype rr, which when crossed results in an all white punnet square.