In which cases should we use " 's "?

In the specific example I would say: "He researched plant leaves."

A general discussion of the plural and/or possessive is beyond my abilities.

poppymanI wonder when we could use 's.

You can almost never go wrong if you use 's after a person's name (John's, Mr. Smith's) or after a noun that represents a person (man's, child's) or after a unit of time (this year's profit, last week's project), and use a compound noun in other cases (table top, kitchen floor).

Thank you CJ and MalRey. "a plant's leaf" is ok then? I know that I can use the plant leaves or a leaf of a plant but not quite sure about a single object.

poppyman"a plant's leaf" is ok then?

How can you conclude that? Is a plant a person? Read the responses again. It's plant leaves.

CJ

Okay, as I understand it, I can use 's only after some animate objects, right?

poppymanOkay, as I understand it, I can use 's only after some animate objects, right?

There you go!

thank you!