Equilibrium is when the concentration is the same throughout an entire system. Explain how a cell reaches equilibrium in all three types of solutions (hypertonic, hypotonic, and isotonic).

It is pertinent to understand what hypertonic, hypotonic, and isotonic solution means before setting out to explain how a cell reaches equilibrium in each type of solution.

A hypertonic solution is one whose solute concentration is higher than that of the sap of a cell that is immersed in it.A hypotonic solution is one with the same solute concentration as that of the sap of the cell immersed in it.An isotonic solution has a lower solute concentration than that of the sap of the cell immersed in it.

In biological systems, water molecules move by osmosis from the region of higher water potential or lower concentration of solutes to the region of lower water potential or higher concentration of solute. An equilibrium is reached when there is no net movement of water between two sides. Hence;

A cell placed in a hypertonic solution will lose water to the surrounding solution until an equilibrium is reached. This means that such a cell will end up shrinking (wilting) or even dying due to loss of water from the cell sap.A cell placed in a hypotonic solution will gain water from the surrounding solution until there is no net movement of water anymore. Such a cell might become turgid or even burst out its cell content.A cell placed in an isotonic solution will neither gain nor lose water because the cell sap and the surrounding solution have equal solute concentrations.

More about osmosis here:

The answer is atmosphere. there are four spheres of the earth: 1. geosphere (from greek word 'geo' = ground), 2. hydrosphere (from greek word 'hydro' = water), 3. biosphere (from greek word 'bio' = life), and 4. atmosphere (from greek word 'atmo' = air). a magnetosphere is a region of space around astronomical objects controlled by the magnetic field of that object. through the process of elimination, since lightning is present in the air, it can be found in the atmosphere.