Alright. So problem to in chapter nine asked us all about signal transaction pathways and asked for an accurate description of them. So, um, first going over our response is a, uh says that, um signals need thio pass through the membrane. B says that, um, cell response on the interior, um, is triggered from an exterior source. C says the opposite of that. That an exterior a sources triggered from something within the cell. And then D says, um, pathways air on lee found when the signal crosses over the membrane. So let's go through these, um A with the necessary for signals to cross the membrane. I'm gonna pop on over here to this diagram. And these signals that are going through our quote going through the membrane aren't really passing through the membrane at all. There are these on the external side of this, so I'm gonna call this the internal side and these Liggins, which we oh thes lie Ganz bond to receptors. Recep tors. So once these two are bonded, um, in the active site than, um in intracellular um, lie again. If you will bonds to the opposite side of this receptor, and there maybe a passage of positive or negative ions, and this pathway could continue into another, um, receptor. And it could keep going, um, until the final product is achieved. So nothing is really passing straight through the membrane. That's not happening. It's all going through the's receptors, so nothing is crossing the membrane. So a is incorrect. Um, be we already talked about this inter cellular response from the external environment. So be, we know has to be correct. See is the opposite. But a signal transaction pathway does not, um, occur out in, um, this, um, open space. It all occurs within within the cell, so see is false. And then D says, is on. Lee found in phase in situations where the signal crosses the membrane. But we already discussed. There's nothing physically permeating the membrane. It's all going through these receptors, so D is false. And the only answer to a problem, too, is B.