Explain why the arrangement of water molecules is different in ice and water

Ice is less dense than water.

First of all, we must bear in mind that ice is a solid and water is a liquid. In ice, the molecules of water are arranged into regular patterns held together by hydrogen bonds forming a rigid crystal lattice with spaces between these lattices. This gives a solid structure in which each water molecule form four hydrogen bonds to other water molecules.  This arrangements takes up a greater volume hence ice is less dense than an equal mass of water.

Water on the other hand is a liquid and the molecules of water are closer to each other and are also held together by hydrogen bonds. Water molecules stick together and take up less space hence water is denser  than an equal mass of ice.

To learn more about hydrogen bonding in ice see:

link

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!