True or false: All substances can pass freely between the intracellular and extracellular fluids through a phospholipid bilayer.

False

Explanation:

IF this were true this would jeopardize internal environment of our cells, similar to how not every key opens a key lock, not every molecule has the "key" to enter the intracellular and extracellular fluids through a phospholipid bilayer. Usually small hydrophobic ("water-hating") can pass through the intracellular and extracellular fluids through a phospholipid bilayer.

this protocol describes a detailed procedure for intracellular flow cytometry staining.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.