Which cellular structure performs the biochemical work of the cell?
a. The cell membrane
b. The cytoplasm
c. The nucleus
d. The organelles
This was a question at work and I have already answered it wrong so it’s not for homework help or anything! How would you answer this?
I said “organelles” because I thought they trigger the activity that goes on. Please help me preserve a thread of my dignity 
You are correct. The cell membrane keeps the cell contents in and the environment out and regulates the passage of nutrients and wates. The cytoplasm provides support for the internal structure of the cell and an aqueous medium for chemical reactions to occur in. The nucleus contains the DNA - the genetic instructions that tell the cell what to do and when to do it. The various organelles take instructions from the nucleus and do chemical work, depending on the instructions - manufacturing proteins, burning fuel for energy, and performing maintenance functions, for example.
It’s the organelles. They do all the work. The membrane is just a wall, the cytoplasm just jello, and the nucleus tells everything else what to do. Of the organelles, the golgi apparatus packages proteins, the mitochondria produce energy, the lysosome digest and store stuff, and there are a bunch of others. Mitochondria have their own DNA and are thought to have orginally been bacteria that have become obligate sympbiotic parasities.
It’s a very poor question, and as it is phrased, essentially unanswerable, since some “biochemical work,” at least in a certain sense, might be considered to go on in the nucleus as well as the cytoplasm. However, I would also consider “organelles” to be the most correct answer, since they are the site of most biochemical synthesis.
I’d have also said “d. The organelles”.
c. is a subset of d. (the nucleus is an organelle), so c. can’t be the right answer.
b. could be the answer, but it’s kind of a matter of whether or not you consider the various non-organelles in a cell to be part of the cytoplasm… or if they’re merely things floating around in the cytoplasm. I don’t like b. as an answer, because it doesn’t meet my idea of a structure performing work. Also, if you count the structures suspended in the cytoplasm… well, the organelles are floating in the cytoplasm, too. Does that mean d. is a subset of b.?
a. while there are certainly cells in which the membrane does a lot of very cool stuff, in a generic “the cell” it’s pretty much just barrier control.
What did they say was the correct answer? Did they give any explanation?
Thanks, guys! They had said the correct answer was cyotplasm, which I thought was just goo containing everything. Armed with confirmation of my original answer I will go back and clarify.
The answer is ‘e. all of the above’. The entire cell–membrane, nucleus, cytoplasm and all–is a biochemical machine.
Technically, the organelles are *part * of the cytoplasm (which includes everything between the nuclear membrane and the exterior cell membrane), so that answer is sort-of-correct. However, I would not regard the cytoplasm itself as a “cellular structure” (although it contains a variety of cellular structures within it), so that it is also sort-of-wrong.
It’s just a very poorly worded question.
Now I’m just here to vent. The passage in the ALAT manual that is referenced says:
The question and this passage could both use a little editing for clarity, but clearly given the wording of the question and this passage, the answer is organelles. Why then do the ALAT exam answers say “cytoplasm”? Because the cytoplasm contains the organelles??? [/rhetorical outburst] ::fume::
What the heck is an “ALAT manual”? And what the heck to they mean by “biochemical work”?
If that’s the passage they cite, then the correct answer clearly cannot be anything other than “organelles.”
Sorry, it’s the manual for training Assistant Lab Animal Technicians (ALATs). It includes basic science info as part of training. I can only hope that the coordinator is mistaken and that the exam doesn’t give the answer she says it did, or else techs trying to pass the test are getting shafted.
That’s a really awful and unfair question. Most of the biochemical work in a cell is performed by organelles – ATP synthesis in the mitochondria, protein modification and folding in the Golgi apparatus, degradation of waste products in the lysosomes, etc. Ribosomes are usually considered organelles, though they don’t have membranes of their own; they’re really just complexes of protein and RNA in the cytoplasm.
So, yes, most of the biochemical work of a cell is performed by the organelles, but crucial biochemical activities occur in all the other parts. Some reactions – notably glycolysis, the first step in carbohydrate metabolism – occur directly in the cytoplasm. Some critical processes involving protein transport and transport and regulation of minerals occur in the cytoplasm.
The cell membrane primarily regulates transport of biochemical products into and out of the cell, but that doesn’t mean they just pass through the cell membrane without any reactions. Many products can only be transported into or out of the cell by some biochemical process – by active transport, which requires ATP to move a product against a concentration gradient. Many membrane proteins have a signaling role, which means they start a series of biochemical reactions that cause the cell to perform a certain function – this should be considered ‘biochemical work’ as well. In some cells, the most important activity occurs on the cell membrane. In neurons, for example, the exchange of sodium and potassium ions that occurs on the cell membrane is without question the cell’s most important function.
Finally, some important reactions do occur in the nucleus, notably DNA transcription (production of messenger RNA copies from sections of the cell’s DNA) as well as DNA replication during cell division and DNA repair.
So all of the answers are really right. To say that the right answer is ‘cytoplasm’ because the organelles are contained in the cytoplasm (or part of it, by some definitions) is asking students to perform a logical jump that isn’t really related to their understanding of cell biology, because they could just as easily choose ‘organelles’ since most reactions occur there. However, by some definitions the organelles (but not the nucleus) are considered to be part of the cytoplasm. If your test uses this definition, then the right answer is ‘cytoplasm’. Again, I don’t think this is really fair, since the word ‘cytoplasm’ is somewhat ambiguous here, and teachers might well use conflicting definitions. (I’d have to look it up to find whether most sources use ‘cytoplasm’ to include the organelles.) This definition would have arisen in a time when microscopes weren’t powerful enough to see the organelles.