I'm not native English speaker and I'm confused about the two following options:
Should I use the possessive apostrophe or not?
Option no.1: They help in carrying oxygen to the body's cells.
Option no.2: They help In carrying oxygen to the body cells.
If you wish to refer to the type of cell then you must use 'body' as an adjective. For example 'cardiac cells', 'vascular cells', 'capillary cells'. There are also a few instances where the noun form is used to refer to the type of cells, e.g. 'blood cells', 'nerve cells', (here the 'blood' and 'nerve' have a adjectival force).
But I think it wouldn't be wise to use 'body cells'. In this case the 'body's cells' is appropriate, and it would be more pleasing to the ears than if you used 'the cells of the body'.
Option #1 sound more natural to my (American layman) ear:
"They help in carrying oxygen to the body's cells."
But this choice is very context related.
If you are emphasizing the distinction between one kind of cell and all other cells, laymen would usually say "body cells". People in the medical profession would usually say "somatic cells", unless they are talking to laymen. For example, "somatic cells" can mean "non-nerve cells", "diploid cells" (as opposed to "haploid cells", or "non-germ-line cells".
The word "somatic" is not natural. Of the people who use it, most were required to consciously learn (or memorize) it as an adult. Ironically, many food marketers use the word "somatic" to imply that a product is "natural".
"Layman" means an ordinary person, as opposed to someone who has been trained in <a learned profession>. In this explanation, "layman" = "someone who is not in the medical profession". The original example was "layman" = "someone who is not a nun, priest, or other member of the clergy". In other contexts, the <learned profession> might be magic, or law, or science.
Definitely, go with Option 1. One can talk about the different types of cells, by saying blood cells and muscle cells. This is another way of saying cells found in the blood and cells found in the muscles. But body cells doesn't work, because there is no one type of cell in the human body.
I'm going to give you a little trick. When you want to figure out which of two constructions works better, try googling two versions of the fragment, in quotation marks. First, check which one gets more hits. Then, if they're both fairly common, check the context to see which one matches up with your situation.
In this case, you would try both
and
If you find you're not getting any relevant hits, try taking some of the words out of the quotation marks.
