Plant cell. It suffers from the classic problem of having too much information about specifics and not enough general information. It lacks a proper lead section, it lacks any real information about function - including the sort of general information you'd expect about water uptake. And yet it mentions phloem loading. There's a lot of different ways a student could improve that article, and it's broad enough that several students could add different (non-overlapping) aspects. If you so desired.
I have not been able to find an overarching article on plant water relations or water movement. Though that might be too much to ask a student to create...
The article on plasmolysis is pretty sad and lacks any references.
Turgor pressure is even thinner and only has a single reference - from an intro biology text (Campbell). And they both suffer from the lack of a 'water relations' article to put them into context.
The water potential article could use someone to translate it into plain English. There are lots of subsections that could use expansion, especially the soil-plant-air continuum one.
I just discovered that there's actually a (very brief) stand-alone article on the soil-plant-air continuum.
The osmosis article could use work, though what it really needs is a complete re-write. As it stands, themechanism section isn't written like an encylopaedia article at all and could use major improvement in tone. t could also use a lot more references.
The osmotic pressure article, like the water potential one, could benefit from more text to complement the equations. It could also do with more references.
The transpiration article could use some work; it's too focussed on leaves, doesn't give a whole-plant sense of things, doesn't have any connection to xylem transport, water uptake
The stomatal conductance article is very short, very mathematical, and short on sources.
The xylem article tries to do too much; in part that's because it was created by merging in an article on "transpirational pull". The section that was created by that merger should be a stand-alone article - probably more than one, but since it isn't, it lacks coherence. Failing that (since it's probably too much to ask of a short course like this one) that part of the article, especially the - subsection on cohesion-tension theory - could be improved, clarified, had better references added.
The "in plants" section of the aquaporin article could probably be expanded.
The symplast article is ever shorter; again, what we really need is an article on water movement at the whole-plant level
There are separate, short articles on the cortex, endodermis and Casparian strip. Ideally these should be tied together with an overarching article on water movement...Sorry, I'm repeating myself. :)
The membrane transport article could use some mention of plants; both this and the active transport article could also use more details of channels, pumps and transporters
The active transport article only mentions plants in passing - it could use a lot more
Ion transporter is very short; ion channel is long, but could be expanded with plant-specific information I suspect. This template lists a number of specific kinds which I think are probably too specific, but there might be something interesting in there.
The moisture stress article is very short. It could be developed in all kinds of different ways.
The physiology section of the plant article says almost nothing on water. While I would normally tell students to stay away from a major article like that, I think some additions would be very helpful (if done right).
The plant physiology article lacks a section on water relations.
Likewise on the abiotic stress article. In both cases, this kind of information could also be added to the main plant physiology or ecophysiology articles, with links to these ones.
The mass flow article could use expansion, or at least correction (it currently says that water moves through mass flow in xylem).
The article on C3 photosynthesis is short and could use expansion. (The C4 and CAM articles are longer, but not without room for improvement.)
Carbon fixation is an overview of a lot of different reactions, but there's room for expansion in a lot of the subsections.
The electrochemical gradient is tagged for a re-write in more easily understandable terms. There might also be some room for improvement.
