Define interstitial fluid, indicating whether it is inside or outside cells (intracellular or extracellular).

Interstitial fluid is the extracellular fluid that is present in the narrow spaces between the cells of tissues.

Explanation:

Depending upon the location, the body fluid can be defined as extracellular or intracellular fluid. The extracellular fluid is the body fluid present outside the cells. Interstitial fluid is extracellular fluid. It is extracellular as it is present in the gaps between the cells of tissues.  

Its composition and function vary with its location in the body. The interstitial fluid serves as a site from where cells take up oxygen and nutrients while releasing the toxic and waste substances into it.

i think its y= -4x-14

it is a limiting nutrient limited by a single nutrient in the ecosystem, & the single goes very slow.