Proteins that span cell membranes, called transmembrane proteins, are often important for recognizing extracellular signals and stimulating a change within the cell. classify the following statements as describing transmembrane proteins that act as ligand-gated ion channels, g-protein-linked receptors, or enzyme-linked receptors. (a) activation by ligands causes a conformational change that allows ions to cross the cell membrane (b) important for action potentials in neurons. (c) activation by ligand releases a protein that binds gtp (d) important for taste. (e) activation by ligand induces a change that causes the transmembrane protein to function as an enzyme (f) important for receiving growth factors

frogs. the lower the ph the higher the acid content. frogs have the highest tolerance in this scenario.

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!

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