How many of the following organisms exchange O2 with CO2 by simple diffusion over their entire body surface?a. Insectsb. Flatwormsc. Earthwormsd. Coelenteratese. Molluscsf. Sponges

Lower invertebrates like sponges, coelenterates, flatworms, etc., exchange O2 with CO2 by simple diffusion over their entire body surface. Earthworms use their moist cuticle.Insects have a network of tubes (tracheal tubes) to transport atmospheric air within the body. Special vascularised structures called gills (branchial respiration) are used by most of the aquatic arthropods and molluscs