One important concept is that typically used reinforcing (post-tensioning tendons and shrinkage-compensating concrete reinforcement are the exceptions) will not prevent the concrete from cracking. The reason for this is that the reinforcing cannot begin to start resisting significant tension until the concrete cracks.
In many bivalves and snails, and in cephalopods, part of the mantle is modified into a siphon, which can be used to pump water through the mantle cavity for respiration, feeding and/or jet propulsion. Freshwater and marine mollusks have gills (called ctenidia) for respiration, located in the mantle cavity.he mantle also secretes the shell, in those mollusks that have one. In many gastropods and cephalopods, the mantle is brightly colored and important for communication. In giant clams, the outer mantle tissue is colonized by symbiotic algae that provide their host with food energy in exchange for shelter.
Structure. The gas exchange organs in fish are the gills, which are near the mouth and are also near the the surface of the skin. They are covered by the operculum which is a flap of skin that protects the gills.. Fish must cope with the buoyancy of the water they live in. They have swim bladders which helps the fish to conserve energy for efficient gas exchange and help them travel at different altitudes in the water. Since humans live on land, there is hardly any buoyant force, so humans do not have swim bladders. 2.