Cartilaginous fish do not contain any bones - their skeleton is made up of cartilage.
Food webs normally start at the bottom and work their way up. Like the plants will be at the bottom, and then each level shows the animals getting bigger while losing energy. You continually lose energy as you work your way up an ecosystem, so normally there are only three or four levels. I hope this helps!
Pinching in of fluids by a unicellular organism is the process of pinocytosis or fluid endocytosis. The cell takes in surrounding fluids, including all of the substances available, without differentiating. It is a non-specific process. The membrane of the unicellular organism elongates, captures the fluid and small vesicles are pinched off intracellularly. These vesicles then are processed by the organelles of the cell.
