Question

a main difference between organisms with simple body plans and those with complex body plans is that
animals with simple body plans have a digestive compartment with one opening, whereas organisms with complex body plans have digestive tubes with two openings.
animals with simple body plans can ingest food while earlier meals are still being digested, whereas animals with complex body plans cannot.
animals with simple body plans have digestive tubes with two openings, whereas organisms with complex body plans have a digestive compartment with one opening.
animals with simple body plans have digestive tubes with specialized compartments, whereas animals with complex body plans do not.
animals with simple body plans eliminate undigested food via an anus, whereas animals with complex body plans eliminate undigested food via a mouth.

Explanation:

To solve this, we analyze each option based on digestive systems of simple and complex body - plan organisms:

1. For option 1: Simple - body - plan organisms (like cnidarians) have a gastrovascular cavity (digestive compartment) with one opening (mouth/anus). Complex - body - plan organisms (like vertebrates) have an alimentary canal (digestive tube) with two openings (mouth and anus). This matches the known anatomy.
2. For option 2: Organisms with a digestive tube (complex body plans) can ingest food while earlier meals are being digested (due to the two - opening system), while those with a single - opening system (simple body plans) cannot. So this option is incorrect.
3. For option 3: It reverses the correct structure of digestive systems. Simple body plans have one - opening compartments, and complex have two - opening tubes. So this is wrong.
4. For option 4: Specialized compartments are a feature of complex body - plan digestive systems, not simple ones. So this is incorrect.
5. For option 5: Organisms with simple body plans (single - opening system) eliminate undigested food through the same opening (not an anus), and complex body - plan organisms eliminate through the anus (not the mouth). So this is wrong.

Answer:

A. animals with simple body plans have a digestive compartment with one opening, whereas organisms with complex body plans have digestive tubes with two openings.