1.) It is True that when a cell is put into an isotonic solution, individual water molecules cannot move back and forth across the cell membrane.
2) It is False that a when a cell is put into a hypertonic solution, there is a net movement of water molecules across the cell membrane into the cell.
3) It is True that when a cell is out into a hypotonic solution, there is net movement.
4) It is False that the movement of any solvent across a semi-permeable membrane is called osmosis.
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Answer:
Microtubules composed of tubulin protein.
Explanation:
The cytoskeleton is composed of three well defined filamentous structures: microtubules, microfilaments, and intermediate filaments. Each of these filamentous structures is a polymer of proteinic subunits united by weak, not covalent connections.
Microtubules are long hollo cylindric tubes with no ramifications of a diametre near to 25 nanometers. They are constituted by two subunits of tubulin protein which polymerize to form microtubules. These filaments shape the cell and are involved in intracellular transport. Microtubules extend from an organizing center near the nucleus to the cellular surface.