100-150 words (need now) Environmental interactions: A human pancreatic cell obtains Oz, fuel molecules such as glucose, and building
materials such as amino acids and cholesterol from its environment, and it releases
co, as a waste product of cellular respiration. In response to hormonal signals, the
cell secretes digestive enzymes. It also regulates its ion concentrations by
exchange with its environment. Based on what you have just learned about the
structure and function of cellular membranes, describe how such a cell
accomplishes these interactions with its environment.

The kidney filters potentially toxic substances in the blood, and thus “clears” the blood of those substances. this clearance function is dependent upon and proportional to the diffusion gradient of the substance across filtering capillaries, i. e. if the concentration of the substance is doubled, twice as much will be cleared from each ml of blood that is filtered. suppose that the body produces a constant amount of a substance x per unit of time. the kidneys eliminate substance x at a rate directly proportional to the concentration of the substance and the volume of blood cleared each minute (c): elimination = c × [x], where [x] is the steady-state concentration of substance x. imagine an individual with an initial concentration of x equal to [x]0 who develops kidney disease. her baseline clearance c0 drops to one half of the original (½c0). what is the new steady state concentration of x? (for simplicity, assume that substance x is 100% filtered by the kidney).