My favorite drink on cold mornings is hot lemonade. I pour 2½ cups of boiling water into my Pyrex measuring cup, stir in ½ cup of honey, then mix in ½ cup of lemon juice. It’s delicious (and soothing on a sore throat if you happen to have a cold).
What’s interesting is that, although the lemonade looks uniform when stirred together, if I only drink one cup and forget about the rest, the leftovers separate. Fluids do that sometimes – if given a chance, the various components settle out.
Blood is like that. It appears to be a thick, red liquid, but in fact has many different components. When it’s being pumped through our bodies, blood stays all mixed together. When a tube of blood is removed from someone’s body it’s possible to separate it into different layers.
Plasma will rise to the top, leaving the heavier blood cells beneath. That’s one way to distinguish the components of blood: cells vs. plasma.
Settling out into different components is the only comparison being made here.