Why is DNA antiparallel? It has double strands complementing each other. The bases in one strand pair with the other bases in the complementary strand. It has a ladder shape. Its double strands run in opposite directions.

DNA is antiparallel because Its double strands run in opposite directions.

Explanation: The antiparallel nature of DNA strands means that as one strand runs in 5'->3' direction, the other strand runs in 3'->5' direction. The two antiparallel DNA strands are not identical in either base sequence or composition rather they are complementary to each other. This means that anywhere thymine base is found in one strand, adenine is present in the other strand and anywhere guanine occurs in one strand, cytosine occurs in the other strand.

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!