If we consider the many embedded structures of the plasma membrane, the transmembrane proteins that help regulate what enters and exits a cell are essential. They help to maintain homeostasis within the cell and allow for the cell to perform its function. Considering the many different transmembrane proteins that exists and the role in the cell, which of the following is true Group of answer choices

a transmembrane protein that contains a receptor site is controlled by the binding or absence of signaling molecules

all choices are true

a transmembrane protein that serves as a channel and utilizes passive diffusion allows for molecules to move freely through them from high to low concentration

a transmembrane protein that serves as a pump or transporter utilizes active transport and ATP to move molecules against their concentration gradient

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!