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I am a student in middle school. My textbook says that

Cytoplasm is the gelatinous liquid part of the cell excluding organelles.

However my teacher said this is wrong. According to her, the correct definition is "The gelatinous liquid part of a cell excluding the nucleus is known as the cytoplasm".

I am confused now as to which is the correct definition. If my teacher's definition is correct, then the organelles (other than nucleus) are part of the cytoplasm.

Is that correct? What is the correct definition?

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    $\begingroup$ Does this answer your question? What is the difference between cytosol and cytoplasm? $\endgroup$
    – tyersome
    Aug 24 at 16:18
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    $\begingroup$ @tyersome — I don’t think it does. It is a different question — the distinction between two terms — and if taken in the context of this question it would imply that one particular definition of cytoplasm is “correct”, which, I argue, is incorrect. $\endgroup$
    – David
    Aug 24 at 17:44
  • $\begingroup$ Edward2007- what an incredible question by such a young mind. I'm impressed that you decided to find out more about the topic and found your way to an open forum like this. While I do not have the exact answer to your question, I do believe that Bryan Krause's response offers a very nice approach about thinking contextually. "The cytoplasm is like the ocean." It depends on how you look at things. Some times it's not very important to get the definition 100% right, but to visualize the bigger concept, for instance the makeup of a cell, in this case. Any way, I'm sure you'll do great with whatev $\endgroup$ Aug 27 at 0:28
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The cytoplasm is like the ocean.

When you talk about the ocean, do you include the fish? What about islands? Sometimes yes, sometimes no.

You could use a cytosol/cytoplasm distinction, where cytosol is "just the liquid part outside the organelles" and cytoplasm includes all the fish, but context matters and I don't think it's actually necessary to have a distinction.

If someone is talking about the "pH of the cytoplasm", you can assume they mean the liquid part, not that they're taking some weighted average of pH over all the different organelles plus the space outside of them. Same thing for ion concentrations. If someone is talking about the "cytoplasmic face" of a membrane, it's clear they mean the side that faces the liquid stuff in cells, even if you're talking about vesicles and organelles where all the membrane faces are "inside the cytoplasm" since the whole organelle is. However, if one were to "remove all the cytoplasm from a cell" you'd expect the organelles (minus the nucleus) to come along; after all, they are in the cytoplasm so they go where it goes.

If you need to memorize a definition for a class, use what the teacher gives you. Otherwise, think critically about the context in which the word is used. I like your teacher's definition better, not because the two options are "liquid only" and "liquid plus organelles", but because organelles are in the cytoplasm, so sometimes when people say cytoplasm they mean the whole ocean including the contents. Your teacher's definition allows for both uses of the term; yours explicitly does not.

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    $\begingroup$ "The cytoplasm is like the ocean.": great analogy! $\endgroup$
    – Our
    Aug 25 at 18:17
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    $\begingroup$ @Bryan given the upvotes taking your post to the top answer, I think it'd be good to provide a cited example (or two) of usages $\endgroup$ Aug 26 at 2:14
  • $\begingroup$ Why doesn't the nucleus go where the cytoplasm goes? It is also in the cytoplasm. $\endgroup$
    – user253751
    Aug 26 at 16:15
  • $\begingroup$ @user253751 The analogy only goes so far, but if I want to take it there then the answer would be that the nucleus in this case is the "continents". Cytoplasm was named by looking at a cell in a microscope and seeing this spherical ball in the center, calling that the nucleus, and needing a name for all the other "stuff". It was only later that it was known what other "stuff" was in the ocean. $\endgroup$
    – Bryan Krause
    Aug 26 at 19:45
  • $\begingroup$ @theforestecologist Yeah, for sure, that would be good. I've tried to find examples that make some of these distinctions I am talking about clear, but that's been a bit difficult. I will certainly try to find the time, though. For now, I'd recommend a reader try searching Google Scholar for these terms: look for papers that talk about the pH of cytoplasm, or look for "cytoplasmic face" in discussions of cellular transport or transmembrane proteins. Or, conversely, look for measurements of "cytoplasm volume" relative to the nucleus. Vacuoles add a bit of complexity if you're into plants, though $\endgroup$
    – Bryan Krause
    Aug 26 at 19:47
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The young scientist asks:

“What is the correct definition?”.

The old scientist answers:

“As is often the case in biology, there is no correct definition — different people adopt different usages.”

This answer attempts to explain why this is the case and how to find out other than asking people who despite greater age and knowledge, may be mistaken in their dogmatism.

General Answer

Often in biology a term is coined for a new observation or concept that has arisen from scientific research. Subsequently further research reveals new aspects or details. These expand rather than negate the original discovery, but can make original definitions inadequate. Individual scientists modify the terminology, and naturally do so in relation to their own concerns, which may differ from those of other scientists. Hence different usages arise.

One might have expected that there would be committees of scientists to lay down rules, but this tends to be confined mainly to the physical and chemical sciences where precise common terminology is important. Because modern biology is fast moving, people are inclined to either wait until the dust has settled (e.g. in enzyme nomenclature) or let “terminological Darwinism” take its course.

Specific Answer

I am not really a biologist in the traditional sense, so I lacked any dogmatic attitude to the question, and, instead made Wikipedia my first port of call. This is not a definitive authority on anything, as anyone can edit it. However in this case it is, I think, useful. Under History we read:

The term was introduced by Rudolf Bon Kölliker in 1863, originally as a synonym for protoplasm, but it later has come to mean the cell substance and organelles outside the nucleus.

There has been a certain disagreement on the definition of cytoplasm as some authors prefer to exclude from it some organelles, especially the vacuoles and sometimes the plastids.

Further in the article there is a reference to the term cytosol which is used in an experimental (rather than an observational) sense to refer to the portion of the cytosol from which membranous organelles have been removed.

The date 1863 is worth noting as it is before the discovery of organelles such as the mitochondrion (1880), and knowledge of others at the time was at a primitive stage.

Addendum: Advice to the young scientist

  • You have eaten from the tree of knowledge and have lost your innocence. Cry a tear then wipe it dry, as you did when you realized there was no Santa Claus. If you wish to become a scientist or even just to understand science you must understand how science works.

  • Do not reproach your teachers. They are fallible because they are human. Be charitable towards them as you would have them be to you.

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It's going to depend on what definition is useful in what context. If was was talking about an mRNA being translated in the cytoplasm, I am saying it is absolutely not translated in the ER or the golgi apparatus. (Most proteins translated in those places are on their way to being transported somewhere else; they will not end up free-floating in the cytosol the way proteins translated in the cytosol usually are)

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If you want to know about biology, go to PubMed. If you want to know about semantics, go to Wikipedia.

Their articles may not be tremendously detailed or accurate overall, but if there is any one thing that inspires generations of bitter snipes and threats, it is a Wikipedia discussion about how to title an article or define the title term. In this case it is perhaps not so severe; nonetheless, their talk page suggests that they've been around this merry-go-round at least two or three times. They seem to stick with the standard idea that cytoplasm = everything but nucleus, cytosol = everything but nucleus and organelles.

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