Why does the plant cell have a cell wall and a cell membrane?

What field of science did harry hess study?

Can someone i have no idea of how to do this.

Which scientific design has both practical limitations and limitations due to scale? studying the effect of bleach on the growth of mold spores exposing cultures of duckweed to different intensities of light observing the replication of dna molecules with a hand lens using colored marbles to model a cross between two colors of rabbits