I believe some of the open panels on the underside of the saucer in the TMP drydock scene were meant to represent cargo bay hatches.
All we know for sure is that these were "loading hatches" of some form.
I would like to make a suggestion, for clarity's sake.
Let's come up with a clear delineation between "ship's stores" and "cargo bays."
CARGO isn't "ship's consumables." Rather, "cargo" is something which is not critical to the function of the ship. "Ship's consumables" are totally different from "cargo." Cargo is something you carry from point "A" to point "B." Carrying cargo is a mission. You're not supposed to "consume" your cargo during a voyage. You're supposed to "transport" it.
These two categories of material are sufficiently different, that I think we need to make every effort to keep them distinct. Do you guys disagree?
Why do I mention this?
Well, I see those hatches on the underside of the TMP Enterprise has being consumables-loading hatches. Not "cargo loading hatches."
I imagine air scrubber filters, and pressurized air tanks (yes, they "recycle" the air but they still need gas storage and it will, inevitably, be "consumed" over time, due to slow leakage or due to damage or to airlock openings or whatever else). They need water. They need "protein packs" which can be used as raw material for food processor/replicator units (again, remember, recycling of... "spent"... food will occur, but you'll still inevitably lose SOME over time). They need non-organic raw materials for part-replication. They need a store of some critical "repair parts" which they won't need to "replicate."
I envision those four larger hatches on the underside of the primary hull as being the "water/atmosphere gear" equipment/storage swap-out locations.
I see the two smaller ones up-front as being the "food" loading ports. (And note that I'm not talking about the landing footpads... in case anyone's confused, look at the blueprints.)
As for the two "airlock ports" (one of which Spock used to go spacewalking)... well, THOSE just seem totally insane to me. Anybody got a good, logical reason why you'd put an airlock in a place like that?