When movement occurs against the concentration gradient (low to high), this requires?

When movement occurs against the concentration gradient (low to high), this requires Active Transport.

Explanation:

Substances moving against the concentration gradient, from a lower concentration area to a higher concentration area requires an active transport. It is termed as  “active” since there is a requirement of energy usage. This process is in contrast with that of a passive transport. Active transport needs carrier proteins for assistance.

Both active transport and facilitated diffusion requires proteins for assistance in transport process. The difference is that, active transport always takes place against the concentration gradient, thereby moving the substances from lower concentration area to a higher concentration area. The types of proteins that are used for transport will not be same.

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!