Abiologist predicted that if part of a leaf is shaded and other parts of the leaf are fully illuminated then equal amounts of starch will subsequently be found in the shaded and illuminated parts of the leaf. on which of the following is this biologist most likely basing his prediction?
1. chlorophyll is present in both the shaded and illuminated parts of the leaf.
2. photosynthesis occurs at an accelerated rate in the shaded parts of the leaf.
3. carbon dioxide and water can enter cells in both the shaded and illuminated parts of the leaf.
4. shading part of the leaf increases the rate at which photosynthesis occurs in the illuminated part of the leaf.
5. starch can move to different parts of the leaf.

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).