Hypotonic, isotonic, hypertonic these terms are connected to the solution concentration. hypotonic solution is the solution with low concentration (lower than the concentration of particles in the living cell of an organism). if you put a cell in such solution, that cell would baloon because of the water migrating inside willing to rebalance the concentrations. isotonic solution is the solution with concentration of particles equal to the concentration inside a cell. hypertonic solution has concentration of particles higher than a cell and putting cell in this solution makes it shrivelled because of the water flowing outside (willing to rebalance concentrations again). that's a phenomenon of osmosis.
Biologists think that endosymbiosis gave rise to mitochondria before plastids partly because: (All eukaryotes have mitochondria whereas many eukaryotes do not have plastids)
