This is the 89th most frequent Portuguese word.
têm
"Have" (third person plural of "ter").
Here, 'têm' is the third person plural present tense of 'ter', indicating they possess something.
Eles têm muitos amigos na escola.
They have many friends at school.
In this context, 'têm' is used to describe a characteristic or feature possessed by plants.
As plantas precisam de água porque têm raízes profundas.
Plants need water because they have deep roots.
The verb 'têm' conveys that the students possess or experience something, in this case, questions or doubt.