I'm studying biology for the first time seriously. I've been reading OpenStax College's material. In the section of "The Cell Membrane", I have the following problem:

Choose the answer that best completes the following analogy: Diffusion is to ________ as endocytosis is to ________.

  1. filtration; phagocytosis
  2. osmosis; pinocytosis
  3. solutes; fluid
  4. gradient; chemical energy

I chose number 1, but the site says the correct answer is number 2. Could someone please explain why?


I chose number 1, because diffusion and filtration were passive ways to transport, while endocytosis and phagocytosis are active. I didn't not take in to account that 2. fitted better, because the osmosis part was confusing me.

  • 1
    $\begingroup$ I'm not sure why this question has 5 upvotes. This is a homework question with no attempt at working out an answer. $\endgroup$
    – James
    Mar 13, 2017 at 5:24
  • $\begingroup$ @James, sorry I thought of writing something else, but since this was an analogy I didn't know what else to put. Is it necessary to delete this? $\endgroup$
    – Ana Galois
    Mar 14, 2017 at 23:44
  • 2
    $\begingroup$ Why was the answer to this question moved to the comments? $\endgroup$
    – canadianer
    Mar 15, 2017 at 0:48
  • $\begingroup$ @AnaGalois It sounds like your question is actually about osmosis rather than anything else. If you are confused about osmosis, then ask a question specifically about whatever is confusing you about osmosis. This sort of MCQ format isn't a good for SE. See this meta discussion. $\endgroup$
    – James
    Mar 15, 2017 at 9:59

1 Answer 1


Osmosis is the diffusion of water. Pinocytosis is the endocytosis of liquid/water.


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