The phloem is often regarded as a relatively straightforward transport system composed of loading (collection), long-distance (transport), and unloading (release) zones.
Not sure why there is 'the' before 'phloem' as phloem is a mass noun and I have seen this word used in many other articles without a 'the'. I believe that this sentence is describing generic phloem, not a specific one, so I don't understand why the article is used.
