Cartilaginous fish do not contain any bones - their skeleton is made up of cartilage.
Answer: the core of the earth heats up the more dense part of the mantle making it less dense.<em> </em>When the less dense part of the mantle rises, the more dense part of the mantle falls, and cools off. This motion continues creating convection currents
Ecosystems can be large and are made of biomes. Some examples of ecosystems are deserts and forests.
Blood needs to flow faster around the body in order to supply the muscles with oxygen for respiration