Can you identify the major theme illustrated by each of the following examples? If necessary, you may review the themes in Chapter 1 of your book. Match the themes on the left with the examples on the right. Not all themes will be used. ResetHelp T cell activation requires specific types of communication. Antigen receptors on T cells only recognize fragments of antigens, and the fragments must be displayed, or presented, on the surface of body cells by special proteins before T cells are activated. A T cell bearing a receptor that matches this antigen fragment binds to both the antigen and self-protein. This three-part interaction among a self-protein, an antigen fragment, and an antigen receptor is required for a T cell to function.

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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if you know your abc's you should be able to get your answer or just use google

you should wear a lead protective shield when having teeth x-rays

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-lavira : )