Step 1: Locate the tapetum in the anther.
The tapetum is the innermost layer of the microsporangium wall in an anther, lying just around the developing pollen mother cells and pollen grains.
Step 2: Rule out the other functions.
Protecting the ovule is the job of the integuments, and helping in fertilization is carried out by the pollen tube and synergid cells, so those functions belong elsewhere. Producing pollen grains is the job of the microspore mother cells themselves, not the tapetum.
Step 3: State the tapetum's actual role.
Being rich in nutrients, the tapetum supplies food material for the growth and development of the pollen grains, and later contributes to the formation of the pollen wall (pollenkitt and sporopollenin precursors).
\[ \boxed{\text{Provides nourishment to pollen grains}} \]